# Dog Bloodwork BUN: What High or Low Levels Mean BUN stands for blood urea nitrogen, a waste product your dog's kidneys filter out of the blood. A high BUN on dog bloodwork often points to dehydration, kidney problems, or other illness, while a low BUN is usually less serious but can still matter. This article explains what the number means, how it pairs with creatinine, and which results need a vet's attention right away. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - BUN measures a waste product from protein breakdown that healthy kidneys remove from the blood. - A high BUN can come from dehydration, kidney disease, a high-protein meal, bleeding in the gut, or other conditions. - A low BUN is often linked to liver problems, a low-protein diet, or pregnancy, and is usually less urgent than a high result. - BUN is read alongside creatinine, a more kidney-specific value, because the two together tell a clearer story. - One abnormal number does not diagnose anything. Your vet combines it with your dog's exam, history, and other tests. ## What Is BUN in a Dog Blood Test? BUN is one of the values on a standard chemistry panel, the blood test your vet runs to check organ function. The liver produces urea as it breaks down protein, and the kidneys filter urea into the urine. BUN measures the nitrogen part of that urea in the bloodstream. Because two organs are involved, the liver and the kidneys, BUN is a general signal instead of a precise one. It rises when the kidneys cannot clear urea fast enough, when the body produces more urea than usual, or when a dog is dehydrated and the blood is more concentrated. It falls when the liver makes less urea or when a dog has less protein to break down. Vets often compare BUN to creatinine, another waste product cleared by the kidneys. Creatinine is less affected by diet and hydration, so it is a more specific marker of kidney filtration. When both BUN and creatinine are high, kidney function is the main concern. When only BUN is high, dehydration or another non-kidney cause is more likely. ## Why Your Vet Runs This Test A chemistry panel with BUN is ordered for many reasons. Your vet may run it during a routine wellness visit, before anesthesia or surgery, or when your dog shows signs like vomiting, drinking more water, urinating more, weight loss, or poor appetite. The test helps your vet: - Screen for kidney disease, especially in senior dogs - Check hydration status - Monitor a dog already diagnosed with kidney disease - Look for problems related to the liver, intestines, or endocrine system - Track how a treatment is working over time BUN also has value beyond the kidneys. A higher BUN-to-albumin ratio has been linked to worse outcomes in dogs with certain serious illnesses. In dogs with pyometra, a uterine infection in unspayed females, a higher ratio before surgery was seen in dogs that did not survive, with a cutoff of 8.935 showing 73.08% sensitivity and 90.91% specificity for predicting mortality [1]. A similar pattern appears in dogs with bacterial pneumonia, where a higher BUN-to-albumin ratio was tied to longer hospital stays, more oxygen needs, and lower odds of survival [2]. In a large study of 327 dogs, nonsurvivors had higher BUN (median 18.8 mg/dL) than survivors (median 16.0 mg/dL), and low albumin was the strongest single predictor of death [3]. These findings do not mean BUN predicts the future on its own. They mean BUN is one piece of a bigger picture your vet uses to judge how sick a dog is. ## How to Prepare for Dog Bloodwork Most BUN tests need little preparation. Your vet will tell you if fasting is required, since some panels include values like cholesterol or glucose that are easier to read on an empty stomach. If fasting is needed, it usually means withholding food for a set number of hours while water stays available. Tell your vet about every medication, supplement, and treat your dog receives. Some drugs and high-protein diets can shift BUN. Bring notes on how much your dog drinks and urinates, any vomiting or diarrhea, and any changes in appetite or energy. These details help your vet interpret the number correctly. If your dog gets stressed at the clinic, ask whether the blood can be drawn quickly at the start of the visit. Stress and struggling can affect some values, though BUN is fairly stable. ## What Happens During the Test A technician draws a small blood sample, usually from a vein in the leg or neck. The sample goes into a tube and is spun down so the serum or plasma can be tested. Many clinics run the chemistry panel in-house and have results within an hour. Others send the sample to a laboratory and get results the next day. The draw takes a minute or two. Most dogs tolerate it well, and sedation is rarely needed. If your dog is anxious, ask about a calm, quiet room or a treat-based distraction. ## Understanding Your Dog's BUN Results ### What a Normal BUN Looks Like Reference ranges vary by laboratory, so always read the range printed on your dog's report. As one example, a study of African wild dogs, a different canid species, reported a BUN reference interval of 13.87 to 39.34 mg/dL [4]. Your dog's lab will provide its own range, and your vet interprets the result against it. ### BUN High in Dog Bloodwork A high BUN is called azotemia. Common causes include: - Dehydration, which concentrates the blood - Kidney disease or kidney injury - A recent high-protein meal - Bleeding into the digestive tract - Heart disease or conditions that reduce blood flow to the kidneys - Urinary blockage, which backs urine up into the kidneys Mild elevations from dehydration often improve with fluids. Larger elevations, especially with a high creatinine, point more strongly toward kidney problems. Your vet may repeat the test after rehydration to see whether the number settles. ### BUN Low in Dog Bloodwork A low BUN is less common and often less alarming. It can happen with: - Liver disease, since the liver makes urea - A low-protein diet or poor protein intake - Pregnancy - Overhydration from excessive fluid intake - Certain medications A low BUN alone rarely triggers urgent treatment. Your vet will look at the rest of the panel, especially liver values and albumin, to decide what it means. ### BUN and Creatinine Together The BUN-to-creatinine ratio helps your vet sort out the cause. A high BUN with a normal creatinine often suggests dehydration or a non-kidney problem. A high BUN with a high creatinine points to the kidneys. A low BUN with a low creatinine can suggest liver disease or low protein intake. Creatinine is not perfect either. It reflects filtration only and can be affected by muscle mass, which limits how early it detects kidney changes in older dogs [5]. Newer markers like SDMA, cystatin C, and urinary NGAL can catch kidney problems before BUN and creatinine rise. In one study, 17 of 61 healthy geriatric dogs had at least one elevated early kidney marker while their BUN and creatinine stayed normal [5]. In dogs with heartworm disease and pulmonary hypertension, urinary NGAL was higher than in dogs without hypertension even though BUN and creatinine were normal [6]. This is why a normal BUN does not always mean normal kidneys. If your dog is older or has a condition that stresses the kidneys, your vet may recommend additional testing. You can read more about how kidney disease is staged in [Dog Kidney Disease: What Do the Stages Mean for Your Dog?](/knowledge/veterinary-medicine/senior-and-chronic-care/dog-kidney-disease-stages). ## Recovery Timeline and Home Care Blood draws are minor procedures, and most dogs need no recovery time. The table below outlines what to expect. | Timeframe | What to Expect | What You Should Do | |---|---|---| | Right after the draw | A small bandage or slight bruise at the site | Keep the area clean, watch for swelling | | First few hours | Normal energy and appetite | Offer water and a normal meal unless fasting was required | | Same day | Results usually available | Discuss the numbers with your vet | | 1 to 3 days | Bruise may fade | Call if the site swells, bleeds, or looks infected | | Follow-up | Recheck bloodwork if values were abnormal | Schedule the recheck your vet recommends | If your dog was fasting, feed a normal meal once your vet says it is fine. If your dog had fluids or other treatment during the visit, follow those instructions instead. ## Possible Complications and Warning Signs Complications from a blood draw are rare. Watch for: - Bleeding that does not stop - Swelling, heat, or redness at the draw site - Limping if the leg vein was used - Fainting or weakness These signs are uncommon and usually mild. Call your vet if they appear. The bigger concern is what the BUN result reveals. A high BUN from kidney disease or dehydration can worsen without treatment. Signs that need attention include vomiting, refusing food, drinking much more or much less than usual, urinating more, weight loss, and unusual tiredness. If your dog stops urinating, that is an emergency. ## Questions to Ask Your Veterinarian - What is my dog's BUN, and what is the normal range for this lab? - Is the creatinine normal, high, or low? - Could dehydration or diet explain this result? - Do we need to repeat the test, and when? - Should we check SDMA, cystatin C, or a urine test? - Does my dog need fluids, a diet change, or medication? - What signs should make me call you right away? Write the answers down. BUN results often get rechecked, and having a record helps you track the trend. ## Limitations and When to Contact a Veterinarian BUN is a screening value, not a diagnosis. It can be normal in early kidney disease and abnormal for reasons that have nothing to do with the kidneys. Your vet needs the full panel, your dog's exam, and often a urine test to reach a conclusion. Individual cases always need a veterinarian's judgment. Call your vet the same day if your dog has a high BUN on a lab report and also shows vomiting, diarrhea, poor appetite, or increased drinking and urinating. Go to an emergency clinic now if your dog: - Cannot urinate or strains with nothing coming out - Collapses, seems disoriented, or has a seizure - Breathes with effort or has pale gums - Has uncontrolled vomiting or bloody diarrhea - Drinks and urinates far more than usual along with sudden weakness Schedule a routine visit if a low BUN appears with no other symptoms, or if your dog is older and has never had a full chemistry panel. If you notice blood in your dog's stool along with changes in appetite or energy, that combination deserves a call too. You can read more about that in [Dog Blood in Stool but Acting Normal: What Does It Mean?](/knowledge/veterinary-medicine/digestive-and-urinary-care/dog-blood-in-stool-acting-normal). ## Frequently Asked Questions ### Does a high BUN always mean kidney failure? No. Dehydration, a high-protein meal, gastrointestinal bleeding, and other conditions can raise BUN without kidney failure. Your vet looks at creatinine and the rest of the panel to tell the difference. A single high BUN is a clue, not a verdict. ### Can BUN be normal if my dog has kidney disease? Yes. BUN and creatinine reflect filtration and can stay normal while other kidney markers are already abnormal. In one study, some healthy older dogs had elevated early kidney markers with normal BUN and creatinine [5]. If your vet suspects kidney disease, ask about SDMA, cystatin C, or a urine test. ### What foods or medications can change BUN? A high-protein meal can raise BUN slightly, and some drugs affect it. Low-protein diets and certain medications can lower it. Tell your vet about everything your dog eats and takes so the result is read correctly. ### How often should BUN be rechecked? It depends on why the test was run. A dehydrated dog may be rechecked within days, while a stable senior dog may be rechecked every few months. Your vet sets the schedule based on your dog's condition and the first result. ### Is a low BUN dangerous? Usually not on its own. A low BUN can reflect liver disease, low protein intake, or pregnancy, and it is often less urgent than a high result. Your vet will check liver values and albumin to decide whether it needs follow-up. If your dog's panel also shows changes in liver enzymes or bilirubin, that context matters. You can learn how those values fit together in [Understanding Dog Blood Tests: Interpreting ALT, AST, ALP and Bilirubin](/knowledge/veterinary-medicine/at-home-diagnostics/understanding-dog-blood-tests-interpreting-alt-ast-alp-and-bilirubin). If your vet mentions protein loss through the kidneys, the urine protein-to-creatinine ratio is explained in [Urinary Protein Creatinine UPC Ratio: Diagnosing Glomerular Disease in Dogs](/knowledge/veterinary-medicine/at-home-diagnostics/urinary-protein-creatinine-upc-ratio-diagnosing-glomerular-disease-in-dogs). ## Related Articles - [Dog Blood in Stool but Acting Normal: What Does It Mean?](/knowledge/veterinary-medicine/digestive-and-urinary-care/dog-blood-in-stool-acting-normal) - [Urinary Protein Creatinine UPC Ratio: Diagnosing Glomerular Disease in Dogs](/knowledge/veterinary-medicine/at-home-diagnostics/urinary-protein-creatinine-upc-ratio-diagnosing-glomerular-disease-in-dogs) - [Understanding Dog Blood Tests: Interpreting ALT, AST, ALP and Bilirubin](/knowledge/veterinary-medicine/at-home-diagnostics/understanding-dog-blood-tests-interpreting-alt-ast-alp-and-bilirubin) - [Dog Kidney Disease: What Do the Stages Mean for Your Dog?](/knowledge/veterinary-medicine/senior-and-chronic-care/dog-kidney-disease-stages) - [Serum Protein Fractions in Veterinary Biochemistry](/knowledge/veterinary-medicine/diagnostics/serum-protein-fractions-in-veterinary-biochemistry-how-to-interpret-hyperglobulinemia-and-hypoalbumi) - [How to Tell If Your Dog Is Overweight: Body Condition Score Explained](/knowledge/veterinary-medicine/preventive-and-routine-care/how-to-tell-if-your-dog-is-overweight-body-condition-score-explained) ## References 1. [Blood urea nitrogen-to-albumin ratio predicts mortality in dogs with pyometra](https://pubmed.ncbi.nlm.nih.gov/41947680/). Journal of veterinary science, 2026. 2. [Retrospective Evaluation of Blood Urea Nitrogen-to-Albumin Ratio as a Novel Biomarker of Illness Severity in Dogs With Bacterial Pneumonia (2018-2023): 30 Cases](https://pubmed.ncbi.nlm.nih.gov/41313644/). Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001), 2025. 3. [Low serum albumin and elevated blood urea nitrogen-to-albumin and creatinine-to-albumin ratios are associated with mortality in dogs](https://pubmed.ncbi.nlm.nih.gov/42248206/). American journal of veterinary research, 2026. 4. [DETERMINATION OF SYMMETRIC DIMETHYLARGININE, CREATININE, AND BLOOD UREA NITROGEN REFERENCE INTERVALS IN AFRICAN WILD DOGS (LYCAON PICTUS) IN MANAGED CARE FROM TWO ZOOLOGICAL INSTITUTIONS IN THE UNITED KINGDOM](https://pubmed.ncbi.nlm.nih.gov/40638183/). Journal of zoo and wildlife medicine : official publication of the American Association of Zoo Veterinarians, 2025. 5. [Serum Cystatin C and the Urinary NAG Index Identify an Altered Renal Biochemical Phenotype in Clinically Healthy Geriatric Dogs with Normal Serum Creatinine: A Three-Tier Cross-Sectional Study](https://pubmed.ncbi.nlm.nih.gov/42797917/). Veterinary sciences, 2026. 6. [Urinary NGAL as an Early Marker of Renal Dysfunction in Dogs with Heartworm Disease and Pulmonary Hypertension](https://pubmed.ncbi.nlm.nih.gov/40723466/). Animals : an open access journal from MDPI, 2025. ## Further Reading - [Merck Veterinary Manual: Dog Owners](https://www.merckvetmanual.com/dog-owners) - [Cornell Richard P. Riney Canine Health Center: Canine Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)