# Urinalysis in Veterinary Medicine ## Quick Answer - Urinalysis interpretation requires integrating physical properties, chemical dipstick findings, and microscopic sediment examination to build a differential diagnosis instead of relying on any single measurement. - Collect urine before treatment begins, use species-appropriate collection methods, and record collection time and method because these factors directly change how results must be read. - A normal urinalysis does not exclude renal disease, and abnormal findings require veterinary interpretation in the context of the full clinical picture. ## Purpose and Scope of Urinalysis in Veterinary Practice Urinalysis is a core diagnostic procedure in veterinary medicine that provides information about the urinary system and systemic metabolic processes. The test is inexpensive, rapid, and can be performed in most clinical settings, making it a practical first-line screening tool for animals presented with signs referable to the urinary tract or with nonspecific illness. The American Veterinary Medical Association emphasizes the importance of regular veterinary examinations for companion animals, and urinalysis is a standard component of these evaluations, particularly in older animals or those with chronic conditions [1]. The test has three main components. Physical examination of urine assesses color, turbidity, and specific gravity. Chemical analysis uses reagent strips to measure pH, protein, glucose, ketones, bilirubin, blood, and other parameters. Microscopic examination of the sediment identifies cells, crystals, casts, and microorganisms. Each component contributes distinct information, and interpretation requires considering all three together. Urinalysis is indicated in several clinical situations. Animals presenting with pollakiuria, dysuria, hematuria, or inappropriate urination require urinalysis to investigate lower urinary tract disease. Animals with polyuria and polydipsia need urinalysis to assess concentrating ability and screen for metabolic disease. Animals receiving long-term medications that affect the kidneys, such as nonsteroidal anti-inflammatory drugs or certain antibiotics, benefit from periodic urinalysis to monitor for adverse effects. Routine wellness screening in older animals includes urinalysis to detect subclinical disease. The test also has limitations. Urinalysis provides a snapshot of the urinary system at the time of collection, and results can change rapidly. A single normal urinalysis does not rule out disease, and a single abnormal finding does not establish a diagnosis. The Merck Veterinary Manual emphasizes that laboratory results must be interpreted in the context of the complete clinical examination and history (Merck Veterinary Manual). Urinalysis is a screening tool that guides further diagnostic testing instead of a definitive test. ## Collection Methods and Their Effect on Interpretation The method of urine collection determines which tests can be reliably interpreted and which findings may be artifacts. Three collection methods are used in veterinary practice: free catch, catheterization, and cystocentesis. Each method has advantages and limitations, and the collection method must be recorded with the results. Free-catch urine is collected by catching urine midstream during natural voiding. This method is noninvasive and does not require sedation. It is the only practical method for many animals, particularly those that are difficult to handle. Free-catch samples are appropriate for physical and chemical analysis. The sample may be contaminated with bacteria from the distal urethra, perineum, or genital tract, so quantitative bacterial culture from free-catch urine is difficult to interpret. The Merck Veterinary Manual notes that free-catch samples are suitable for routine urinalysis but that culture results must be interpreted with caution due to potential contamination (Merck Veterinary Manual). Catheterization involves passing a sterile urinary catheter through the urethra into the bladder. This method reduces contamination compared to free-catch collection and allows collection when the animal cannot void voluntarily. Catheterization carries a small risk of introducing bacteria into the bladder, so strict aseptic technique is required. The procedure may cause transient hematuria, which can confound the interpretation of blood on the reagent strip and red blood cells in the sediment. Cystocentesis is the collection of urine directly from the bladder using a needle and syringe, guided by palpation or ultrasound. This method provides the least contaminated sample and is the preferred method for urine culture. Cystocentesis requires technical skill and is not appropriate for all animals. It is contraindicated in animals with bleeding disorders, and the procedure can cause hematuria. The World Small Animal Veterinary Association provides global guidance on clinical practice standards, and the choice of collection method should follow established veterinary protocols (WSAVA Global Guidelines). The timing of collection also affects results. Urine collected in the morning is more concentrated and may reveal abnormalities that are diluted in less concentrated samples. Urine that is collected after the animal has been drinking heavily may have a lower specific gravity. The time of collection relative to feeding affects the presence of glucose and other metabolites. The time of collection should be recorded with the results. ### Sample Handling and Storage Urine is an unstable biological sample. Chemical changes begin immediately after collection. Bacteria multiply in urine at room temperature, and cells and crystals degrade over time. The urine should be analyzed within 30 to 60 minutes of collection for the most accurate results. If analysis is delayed, the sample should be refrigerated, but refrigeration also changes the sample. Refrigerated urine may develop crystals that were not present in the fresh sample, and the specific gravity may be affected. The sample should be warmed to room temperature before analysis. The American Animal Hospital Association provides practice guidelines for companion-animal care, and these guidelines emphasize the importance of proper sample handling for accurate diagnostic results (AAHA Guidelines). The sample container should be clean and sterile for culture. The sample should be protected from light, which can degrade bilirubin and other light-sensitive compounds. ## Physical Examination of Urine The physical examination of urine provides initial information that guides the rest of the analysis. The color, turbidity, and specific gravity are assessed. ### Urine Color Normal urine color ranges from pale yellow to amber, depending on the concentration of urochrome pigments. The color is affected by the specific gravity, with more concentrated urine appearing darker. Abnormal colors indicate the presence of substances that are not normally present in urine. Red or brown urine indicates the presence of blood, hemoglobin, or myoglobin. Red urine with red blood cells in the sediment indicates hematuria. Red urine without red blood cells may indicate hemoglobinuria or myoglobinuria. Dark brown or black urine can indicate the presence of bilirubin, which is more common in animals than in humans. The color of the urine should be recorded as part of the physical examination. ### Urine Turbidity Normal urine is clear. Turbidity, or cloudiness, can be caused by cells, crystals, bacteria, or mucus. The degree of turbidity is often described as clear, slightly cloudy, cloudy, or very cloudy. Turbidity is not a specific finding, and the cause is identified by microscopic examination of the sediment. A cloudy sample with a high specific gravity may contain crystals. A cloudy sample with a low specific gravity may contain cells or bacteria. ### Urine Specific Gravity Specific gravity measures the concentration of dissolved particles in the urine. It is a measure of the kidney's ability to concentrate or dilute the urine. The specific gravity is measured using a refractometer, which is the most accurate method. Reagent strips have a specific gravity pad, but the strip measurement is less accurate than the refractometer and should not be used for clinical decisions. The normal range for specific gravity varies by species. In dogs, the normal range is approximately 1.015 to 1.045. In cats, the normal range is approximately 1.020 to 1.040. The specific gravity is interpreted in the context of the animal's hydration status. A specific gravity that is fixed at a low value, such as 1.008 to 1.012, indicates that the kidney is unable to concentrate urine, which is a sign of kidney disease. A specific gravity that is very high, such as greater than 1.040, indicates that the kidney is concentrating urine appropriately. The specific gravity is a critical measurement because it determines whether the kidney is functioning normally. The Merck Veterinary Manual describes the urine specific gravity as a measure of the kidney's ability to concentrate urine, and it is an important component of the urinalysis (Merck Veterinary Manual). ## Chemical Analysis of Urine The chemical analysis of urine uses reagent strips that change color in the presence of specific substances. The strips are read at a specific time after the urine is applied, and the color change is compared to a chart. The chemical analysis provides information about the pH, protein, glucose, ketones, bilirubin, blood, and other parameters. ### Urine pH Urine pH is a measure of the acidity or alkalinity of the urine. The normal pH of urine varies by species and diet. In dogs and cats, the normal pH is approximately 6.0 to 7.0. The pH is affected by the diet, with high-protein diets producing more acidic urine and high-carbohydrate diets producing more alkaline urine. The pH is important for the interpretation of crystals in the urine. Struvite crystals form in alkaline urine, and calcium oxalate crystals form in acidic urine. The pH can be used to guide the management of urinary stones. The pH is also affected by systemic acid-base status, and a persistently abnormal pH may indicate a metabolic disorder. ### Urine Protein Protein is not normally present in the urine in significant amounts. The presence of protein in the urine is called proteinuria. The reagent strip measures the concentration of protein in the urine, but the result is affected by the specific gravity of the urine. A concentrated urine sample may have a higher protein reading than a dilute sample with the same amount of protein. The protein-to-creatinine ratio is a more accurate measure of protein loss and is used to quantify proteinuria. Proteinuria can be caused by several conditions. It can be caused by kidney disease, where the glomerulus is damaged and allows protein to pass into the urine. It can be caused by inflammation in the urinary tract, where protein is released from the cells. It can be caused by blood in the urine, which adds protein to the sample. The presence of protein in the urine should be interpreted in the context of the other findings. ### Urine Glucose Glucose is not normally present in the urine. The presence of glucose in the urine is called glucosuria. Glucosuria occurs when the blood glucose concentration exceeds the renal threshold, which is the concentration at which the kidney can no longer reabsorb all of the glucose. The renal threshold varies by species. In dogs, the renal threshold is approximately 180 to 220 mg/dL. In cats, the renal threshold is approximately 200 to 280 mg/dL. Glucosuria is most commonly caused by diabetes mellitus. It can also be caused by stress, which can cause a transient increase in blood glucose. The presence of glucose in the urine should be confirmed by measuring the blood glucose concentration. The Merck Veterinary Manual describes diabetes mellitus as a common cause of glucosuria in dogs and cats (Merck Veterinary Manual). ### Urine Ketones Ketones are produced when the body metabolizes fat for energy. The presence of ketones in the urine is called ketonuria. Ketonuria occurs when the body is in a state of ketosis, which can be caused by diabetes mellitus, starvation, or a high-fat diet. Ketonuria is a serious finding that requires immediate veterinary attention. ### Urine Bilirubin Bilirubin is a breakdown product of hemoglobin. It is not normally present in the urine in significant amounts. The presence of bilirubin in the urine is called bilirubinuria. Bilirubinuria can be caused by liver disease, bile duct obstruction, or hemolysis. The presence of bilirubin in the urine should be interpreted in the context of the other findings. ### Urine Blood The reagent strip detects the presence of blood in the urine. The strip detects hemoglobin, which is released from red blood cells. The strip can be positive for blood when red blood cells are present in the urine, when hemoglobin is present in the urine, or when myoglobin is present in the urine. The presence of blood in the urine is called hematuria, and it is a common finding in urinary tract disease. ## Microscopic Examination of Urine Sediment The microscopic examination of the urine sediment is the most informative part of the urinalysis. The sediment is prepared by centrifuging a sample of urine and examining the pellet under a microscope. The sediment contains cells, crystals, bacteria, and other structures that are not visible in the urine. ### Preparation of the Sediment The sediment is prepared by placing a sample of urine in a centrifuge tube and spinning it at a low speed for a few minutes. The supernatant is decanted, and the pellet is resuspended in a small amount of urine. A drop of the resuspended sediment is placed on a slide and covered with a coverslip. The slide is examined under a microscope at low and high magnification. The sediment should be examined within 30 minutes of collection. The urine should be fresh, and the sediment should be examined before the urine is refrigerated. The number of cells and crystals in the sediment is reported as a count per high-power field or low-power field. ### Red Blood Cells Red blood cells are not normally present in the urine in significant numbers. The presence of red blood cells in the urine is called hematuria. Hematuria can be caused by inflammation, infection, trauma, or neoplasia of the urinary tract. The presence of red blood cells in the urine should be interpreted in the context of the other findings. ### White Blood Cells White blood cells are not normally present in the urine in significant numbers. The presence of white blood cells in the urine is called pyuria. Pyuria is a sign of inflammation or infection of the urinary tract. The presence of white blood cells in the urine should be interpreted in the context of the other findings. ### Epithelial Cells Epithelial cells are cells that line the urinary tract. They are normally present in the urine in small numbers. The presence of large numbers of epithelial cells can indicate inflammation or damage to the urinary tract. The type of epithelial cell can indicate the location of the damage. Squamous epithelial cells are from the distal urethra and the vagina. Transitional epithelial cells are from the bladder and the ureters. Renal tubular epithelial cells are from the kidney. ### Crystals Crystals are formed when the urine is supersaturated with a particular substance. The presence of crystals in the urine is called crystalluria. Crystals can be normal or abnormal, depending on the type and the amount. The type of crystal is identified by its shape and the pH of the urine. Struvite crystals are formed in alkaline urine and are composed of magnesium ammonium phosphate. They are common in dogs and cats and are often associated with urinary tract infections. Calcium oxalate crystals are formed in acidic urine and are composed of calcium oxalate. They are common in dogs and cats and are associated with the formation of calcium oxalate stones. Urate crystals are formed in acidic urine and are associated with liver disease and certain breeds. Cystine crystals are formed in acidic urine and are associated with a genetic disorder. The presence of crystals in the urine does not necessarily indicate that the animal has urinary stones. Crystals can be present in the urine of healthy animals. The presence of crystals should be interpreted in the context of the other findings. ### Bacteria Bacteria are not normally present in the urine. The presence of bacteria in the urine is called bacteriuria. Bacteriuria can be caused by a urinary tract infection. The presence of bacteria in the urine should be confirmed by a urine culture. The urine culture is the definitive test for a urinary tract infection. ### Casts Casts are cylindrical structures that are formed in the renal tubules. They are composed of protein and cells. The presence of casts in the urine is called cylindruria. Casts are a sign of kidney disease. The type of cast can indicate the type of kidney disease. Hyaline casts are composed of protein and are present in the urine of animals with kidney disease. Cellular casts are composed of cells and are present in the urine of animals with inflammation of the kidney. ## Interpretation of Urinalysis Results The interpretation of urinalysis results requires the integration of the physical, chemical, and microscopic findings. The results are interpreted in the context of the animal's signalment, history, and clinical signs. The urinalysis is a screening test, and the results are used to guide further diagnostic testing. ### A Structured Interpretation Framework The following framework can be used to interpret urinalysis results in a structured manner. The framework is designed to help the veterinarian identify the most likely differential diagnoses and to determine the next steps in the diagnostic plan. 1. **Assess the specific gravity.** The specific gravity determines whether the urine is concentrated or dilute. A specific gravity that is fixed at a low value indicates that the kidney is unable to concentrate urine. This is a sign of kidney disease. 2. **Assess the pH.** The pH determines the type of crystals that are likely to be present. The pH is also important for the management of urinary tract infections. 3. **Assess the protein.** The presence of protein in the urine is a sign of kidney disease or inflammation of the urinary tract. The protein should be quantified with a protein-to-creatinine ratio. 4. **Assess the glucose.** The presence of glucose in the urine is a sign of diabetes mellitus. The blood glucose should be measured to confirm the diagnosis. 5. **Assess the ketones.** The presence of ketones in the urine is a sign of ketosis. This is a serious finding that requires immediate veterinary attention. 6. **Assess the bilirubin.** The presence of bilirubin in the urine is a sign of liver disease or bile duct blockage. 7. **Assess the blood.** The presence of blood in the urine is a sign of hematuria. The source of the blood should be identified. 8. **Assess the sediment.** The sediment is examined for the presence of cells, crystals, and bacteria. The presence of white blood cells and bacteria indicates a urinary tract infection. The presence of casts indicates kidney disease. ### Common Patterns of Urinalysis Findings The following patterns of urinalysis findings are commonly encountered in veterinary practice. These patterns are not diagnostic, but they can guide the differential diagnosis. - **Hematuria with pyuria and bacteriuria:** This pattern is consistent with a urinary tract infection. The urine should be cultured to identify the bacteria and determine the appropriate antibiotic. - **Hematuria without pyuria:** This pattern is consistent with a stone, a tumor, or trauma to the urinary tract. The urinary tract should be imaged to identify the cause. - **Proteinuria with a low specific gravity:** This pattern is consistent with kidney disease. The protein-to-creatinine ratio should be measured to quantify the proteinuria. - **Glucosuria with ketonuria:** This pattern is consistent with diabetes mellitus. The blood glucose should be measured to confirm the diagnosis. - **Crystalluria with a specific pH:** This pattern is consistent with a stone-forming tendency. The type of crystal should be identified to guide the management. ## At a Glance The following table summarizes the key components of the urinalysis and the interpretation of the findings. | Component | Normal Finding | Abnormal Finding | Interpretation | | :--- | :--- | :--- | :--- | | Specific gravity | 1.015 to 1.045 (dog), 1.020 to 1.040 (cat) | Less than 1.012 | Kidney disease, diabetes insipidus, or overhydration | | pH | 6.0 to 7.0 | Less than 6.0 or greater than 7.0 | Acidic urine is associated with calcium oxalate crystals, alkaline urine is associated with struvite crystals | | Protein | Negative or trace | Positive | Proteinuria, which can be caused by kidney disease, inflammation, or blood | | Glucose | Negative | Positive | Glucosuria, which is most commonly caused by diabetes mellitus | | Ketones | Negative | Positive | Ketonuria, which is a sign of ketosis | | Bilirubin | Negative | Positive | Bilirubinuria, which is a sign of liver disease or bile duct blockage | | Blood | Negative | Positive | Hematuria, which can be caused by inflammation, infection, trauma, or stones | | White blood cells | 0 to 2 per high-power field | Greater than 2 per high-power field | Pyuria, which is a sign of inflammation or infection | | Red blood cells | 0 to 2 per high-power field | Greater than 2 per high-power field | Hematuria, which can be caused by inflammation, infection, trauma, or stones | | Bacteria | Negative | Positive | Bacteriuria, which is a sign of a urinary tract infection | | Crystals | Negative | Positive | Crystalluria, which can be a normal finding or a sign of a stone-forming tendency | | Casts | Negative | Positive | Cylindruria, which is a sign of kidney disease | ## Common Failure Patterns in Urinalysis Interpretation Several common errors can lead to misinterpretation of urinalysis results. These errors can be avoided by following a structured approach to the interpretation. ### Failure to Consider the Specific Gravity The specific gravity is the most important measurement in the urinalysis. It determines whether the urine is concentrated or dilute. The specific gravity affects the interpretation of the other findings. A dilute urine can have a lower protein reading than a concentrated urine with the same amount of protein. A dilute urine can have a lower specific gravity than a concentrated urine with the same amount of crystals. The specific gravity should be interpreted in the context of the animal's hydration status. ### Failure to Consider the Collection Method The collection method affects the interpretation of the findings. A free-catch sample can be contaminated with bacteria from the distal urethra. A catheterized sample can be contaminated with bacteria from the urethra. A cystocentesis sample is the most accurate for culture. The collection method should be recorded with the results. ### Failure to Consider the Timing of the Analysis The urine should be analyzed within 30 to 60 minutes of collection. If the urine is not analyzed promptly, the cells and crystals can degrade. The urine should be refrigerated if it cannot be analyzed promptly. The urine should be warmed to room temperature before analysis. ### Failure to Consider the Clinical Context The urinalysis is a screening tool. The results should be interpreted in the context of the animal's clinical picture. A single abnormal finding does not establish a diagnosis. The urinalysis should be used to guide further diagnostic testing. ## Records and Measurements The urinalysis results should be recorded in the animal's medical record. The record should include the date and time of collection, the collection method, the physical examination findings, the chemical analysis findings, and the microscopic examination findings. The record should also include the clinical context and the interpretation of the results. The following measurements should be recorded for each urinalysis: - **Specific gravity:** Measured with a refractometer. - **pH:** Measured with a reagent strip. - **Protein:** Measured with a reagent strip or a protein-to-creatinine ratio. - **Glucose:** Measured with a reagent strip. - **Ketones:** Measured with a reagent strip. - **Bilirubin:** Measured with a reagent strip. - **Blood:** Measured with a reagent strip. - **Red blood cells:** Counted per high-power field. - **White blood cells:** Counted per high-power field. - **Epithelial cells:** Counted per high-power field. - **Crystals:** Identified by type and counted per low-power field. - **Bacteria:** Identified by presence or absence. - **Casts:** Identified by type and counted per low-power field. The records should be reviewed periodically to identify trends. A trend of increasing proteinuria or decreasing specific gravity can indicate progressive kidney disease. A trend of recurrent urinary tract infections can indicate a structural abnormality of the urinary tract. ## Quality and Welfare Controls The quality of the urinalysis is determined by the quality of the sample and the quality of the analysis. The sample should be collected using a clean container and a sterile container for culture. The analysis should be performed by a trained professional using calibrated equipment. The reagent strips should be stored according to the manufacturer's instructions and should not be used after the expiration date. The welfare of the animal should be considered during the collection of the urine. The collection method should be the least stressful method that is appropriate for the animal. The animal should be handled gently and with care. The collection of the urine should not cause unnecessary pain or distress. The World Organisation for Animal Health provides guidance on the welfare of animals in veterinary care (WOAH Animal Health and Welfare). The welfare of the animal should be a primary consideration in all veterinary procedures. ## Limitations of Urinalysis Urinalysis has several limitations that should be considered when interpreting the results. ### False Positives and False Negatives The reagent strips can produce false-positive and false-negative results. A false-positive result is a positive result when the substance is not present. A false-negative result is a negative result when the substance is present. The false-positive and false-negative results can be caused by the presence of interfering substances in the urine, the pH of the urine, or the specific gravity of the urine. ### The Need for Culture The presence of bacteria in the urine is not a definitive diagnosis of a urinary tract infection. The urine should be cultured to identify the bacteria and determine the susceptibility to antibiotics. The culture is the definitive test for a urinary tract infection. ### The Need for Other Tests The urinalysis is a screening tool. The results are used to guide further diagnostic testing. The urinalysis does not provide a definitive diagnosis. The diagnosis is made by integrating the urinalysis results with the clinical picture and the results of other tests. ## Professional Escalation Criteria The following criteria indicate that the animal should be referred to a specialist or that additional diagnostic testing is required. - **Persistent proteinuria:** A protein-to-creatinine ratio that is persistently elevated indicates significant proteinuria. The animal should be evaluated for kidney disease. - **Persistent glucosuria:** The blood glucose should be measured to confirm the diagnosis of diabetes mellitus. The animal should be evaluated for diabetes. - **Persistent ketonuria:** Ketonuria is a serious finding that requires immediate veterinary attention. The animal should be evaluated for diabetic ketoacidosis. - **Persistent hematuria:** The source of the blood should be identified. The animal should be evaluated for a stone, a tumor, or a structural abnormality of the urinary tract. - **Recurrent urinary tract infections:** The animal should be evaluated for a structural abnormality of the urinary tract or a predisposing condition. - **Casts in the urine:** The presence of casts in the urine is a sign of kidney disease. The animal should be evaluated for kidney disease. ## A Practical Decision Framework for Urinalysis Result Integration The structured interpretation framework in the preceding section lists findings in sequence, but clinical practice requires a faster method to move from raw results to a working diagnosis. A decision framework that groups findings by organ system and pathophysiologic mechanism helps the veterinarian avoid the common error of treating each abnormal value as an isolated problem. The framework below organizes urinalysis results into four functional categories: filtration integrity, tubular function, lower urinary tract status, and metabolic spillover. Each category points to a distinct set of differential diagnoses and next steps. ### Filtration Integrity Assessment The filtration category addresses whether the glomerulus is retaining large molecules and cells. The key findings are protein, red blood cells, and casts. When protein and red blood cells appear together, the clinician must determine whether the blood is contributing the protein or whether the glomerulus is leaking both. A urine sample with visible hematuria will show a positive protein pad even in a healthy kidney because the reagent strip detects protein from lysed red cells. The protein-to-creatinine ratio is the corrective measurement because it normalizes protein concentration to urine concentration and is not falsely elevated by red blood cells alone. The decision rule for this category is straightforward. If protein is positive and the specific gravity is low, the kidney is the likely source. If protein is positive and the specific gravity is high, the protein may be concentrated normally, and the finding should be confirmed with a protein-to-creatinine ratio. If red blood cells are present in large numbers, the protein reading should be interpreted with caution until the hematuria is explained. The Merck Veterinary Manual describes proteinuria as a finding that requires quantification and serial monitoring to distinguish transient from persistent protein loss (Merck Veterinary Manual). ### Tubular Function The tubular function category assesses the kidney's ability to concentrate urine and to handle filtered solutes. The specific gravity is the primary indicator, and the presence of casts is the secondary indicator. A fixed specific gravity below 1.012 in a dehydrated animal indicates that the renal tubules cannot respond to antidiuretic hormone. This finding is more significant than any other single measurement because it reflects a structural or functional loss of tubular capacity. Casts are the second indicator in this category. Hyaline casts appear in the urine when protein is present in the tubular lumen, and cellular casts indicate active tubular injury. The presence of casts should trigger a search for the underlying cause of tubular damage, including ischemia, toxin exposure, or pyelonephritis. The World Small Animal Veterinary Association global guidelines emphasize that clinical decisions should follow established protocols, and the finding of casts is a protocol trigger for further renal evaluation (WSAVA Global Guidelines). ### Lower Urinary Tract Assessment The lower urinary tract category combines white blood cells, bacteria, and the physical appearance of the urine. The decision here is whether the findings indicate inflammation, infection, or both. White blood cells in the sediment indicate inflammation, but they do not confirm infection. Bacteria in the sediment support infection, but the definitive confirmation requires culture. The collection method determines how much weight the bacteriuria finding carries. A cystocentesis sample with bacteria is strong evidence of infection, while a free-catch sample with bacteria may represent contamination from the distal urethra. The decision rule for this category is to culture any sample with white blood cells and bacteria, and to culture a cystocentesis sample with bacteria even if white blood cells are absent. The American Animal Hospital Association provides practice guidance for companion-animal care, and this guidance supports the use of culture to confirm infection before antibiotic selection (AAHA Guidelines). The culture result should be interpreted with the collection method recorded in the medical record. ### Metabolic Contamination The metabolic contamination category identifies substances that should not appear in urine because they are filtered and reabsorbed by the healthy nephron. Glucose, ketones, and bilirubin are the three markers in this category. Glucosuria with a normal blood glucose indicates a renal tubular reabsorption defect, while glucosuria with hyperglycemia indicates diabetes mellitus. The distinction requires a blood glucose measurement, and the urinalysis alone cannot make this separation. Ketonuria is a metabolic emergency indicator. The presence of ketones in the urine means the body is using fat as the primary energy source, which occurs in diabetic ketoacidosis, starvation, or prolonged fasting. The decision rule is to measure blood glucose and assess acid-base status immediately when ketones are present. Bilirubinuria in dogs is a less specific finding because dogs can have trace bilirubin in concentrated urine, but bilirubinuria in cats is always abnormal and warrants a liver evaluation. The Cornell University College of Veterinary Medicine provides educational resources that describe the species differences in bilirubin handling (Cornell University College of Veterinary Medicine). ### The Decision Matrix The following matrix combines the four categories into a practical decision tool. The veterinarian reads the urinalysis and assigns each finding to a category, then uses the category to select the next diagnostic step. | Category | Key Findings | Next Diagnostic Step | Escalation Trigger | | :--- | :--- | :--- | :--- | | Filtration integrity | Protein, red blood cells | Protein-to-creatinine ratio, blood pressure measurement | Persistent proteinuria with a ratio above 2.0 | | Tubular function | Low specific gravity, casts | Serum chemistry, symmetric dimethylarginine | Fixed specific gravity below 1.012 with dehydration | | Lower urinary tract | White blood cells, bacteria | Urine culture, imaging | Recurrent infection or culture with resistant bacteria | | Metabolic contamination | Glucose, ketones, bilirubin | Blood glucose, acid-base assessment | Ketonuria with hyperglycemia | ### Applying the Framework to a Case Example A 9-year-old cat presents with a two-week history of increased drinking and urination. The urinalysis shows a specific gravity of 1.010, a pH of 6.5, negative protein, negative glucose, negative ketones, and no cells or casts in the sediment. The decision matrix places this result in the tubular function category because the specific gravity is fixed at a low value. The next step is serum chemistry and a renal function test. The absence of protein and casts does not exclude kidney disease, and the low specific gravity is the finding that drives the diagnostic plan. A second case involves a 6-year-old dog with straining to urinate. The urinalysis shows a specific gravity of 1.030, a pH of 8.0, positive protein, positive blood, and many white blood cells and struvite crystals in the sediment. The decision matrix places this result in the lower urinary tract category because the white blood cells and crystals dominate the picture. The protein and blood are likely secondary to the inflammation. The next step is a urine culture and imaging to assess for stones. The protein reading should not be interpreted as kidney disease until the inflammation is treated and the urinalysis is repeated. ### Recording the Decision The decision framework should be recorded in the medical record as a structured note. The note should list the category, the key findings, the next step, and the rationale. This structure allows the next veterinarian to understand the clinical reasoning and to track the outcome of the diagnostic plan. The American Veterinary Medical Association provides guidance on the importance of veterinary examinations and the value of structured medical records for continuity of care (AVMA Pet Care). The framework does not replace clinical judgment. It provides a consistent starting point for interpretation and a method for teaching the integration of urinalysis findings. The veterinarian who uses the framework will identify the dominant category and then adjust the plan based on the individual animal's history and physical examination. The framework is a tool for organizing information, not a substitute for the clinical assessment. ## Frequently Asked Questions ### What is the most important measurement in a urinalysis? The specific gravity is the most important measurement in a urinalysis. It determines whether the urine is concentrated or dilute, and it affects the interpretation of the other findings. A low specific gravity indicates that the kidney is unable to concentrate urine, which is a sign of kidney disease. ### How is urine collected for a urinalysis? Urine can be collected by free catch, catheterization, or cystocentesis. Free catch is the least invasive method, but the sample can be contaminated with bacteria. Cystocentesis is the most accurate method for culture. The collection method should be recorded with the results. ### How long can urine be stored before analysis? Urine should be analyzed within 30 to 60 minutes of collection. If the analysis is delayed, the urine should be refrigerated. The urine should be warmed to room temperature before analysis. ### What does the presence of blood in the urine mean? The presence of blood in the urine is called hematuria. Hematuria can be caused by inflammation, infection, trauma, or stones of the urinary tract. The source of the blood should be identified. ### What does the presence of glucose in the urine mean? The presence of glucose in the urine is called glucosuria. Glucosuria is most commonly caused by diabetes mellitus. The blood glucose should be measured to confirm the diagnosis. ### What does the presence of crystals in the urine mean? The presence of crystals in the urine is called crystalluria. Crystalluria can be a normal finding or a sign of a stone-forming disorder. The type of crystal should be identified to guide the treatment. ### What does the presence of casts in the urine mean? The presence of casts in the urine is called cylindruria. Casts are a sign of kidney disease. The type of cast can indicate the type of kidney disease. ### When should a urine culture be performed? A urine culture should be performed when the urinalysis indicates a urinary tract infection. The culture is the definitive test for a urinary tract infection. The culture should be performed on a sample collected by cystocentesis to avoid contamination. ## Related Veterinary Guides - [Problem-Oriented Approach in Veterinary Medicine: A Clinical Framework](/knowledge/veterinary-medicine/clinical-skills-training/problem-oriented-approach-veterinary-medicine-clinical-framework) - [Urinalysis in Veterinary Practice: From Collection to Interpretation](/knowledge/veterinary-medicine/clinical-pathology/urinalysis-veterinary-practice-collection-interpretation) - [Differential Diagnosis in Pathology: A Structured Approach](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/differential-diagnosis-in-pathology-a-structured-approach) - [Veterinary Treatment Plan Development: A Structured Approach](/knowledge/veterinary-medicine/clinical-skills-training/veterinary-treatment-plan-development-structured-approach) - [Monitoring Pain Management in Veterinary Patients: A Structured Approach](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-pain-management-veterinary-structured-approach) ## References and Further Reading - [Pet Care](https://www.avma.org/resources-tools/pet-owners). American Veterinary Medical Association. - [AAHA Guidelines](https://www.aaha.org/resources). American Animal Hospital Association. - [Global Guidelines](https://wsava.org/global-guidelines). World Small Animal Veterinary Association. - [Merck Veterinary Manual](https://www.merckvetmanual.com/). Merck Veterinary Manual. - [Cornell University College of Veterinary Medicine](https://www.vet.cornell.edu/). Cornell University. - [Animal Health and Welfare](https://www.woah.org/en/what-we-do/animal-health-and-welfare). World Organisation for Animal Health. - [Urinalysis.](https://pubmed.ncbi.nlm.nih.gov/26002794). The Veterinary clinics of North America. Small animal practice, 2015. - [Importance of Urinalysis.](https://pubmed.ncbi.nlm.nih.gov/30591190). The Veterinary clinics of North America. Small animal practice, 2019. - [Miniature pigs.](https://pubmed.ncbi.nlm.nih.gov/11229041). The veterinary clinics of North America. Exotic animal practice, 1999. - [Clinical pathology interpretation in geriatric veterinary patients.](https://pubmed.ncbi.nlm.nih.gov/22720804). The Veterinary clinics of North America. Small animal practice, 2012. - [Urinalysis in dog and cat: A review.](https://pubmed.ncbi.nlm.nih.gov/33281347). Veterinary world, 2020. > This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.