# Bone Marrow Aspiration and Biopsy: Indications and Interpretation


## Key Takeaways

- Bone marrow evaluation is indicated for unexplained cytopenias (anemia, leukopenia, thrombocytopenia), bicytopenias, pancytopenias, suspected marrow neoplasia, unexplained leukocytosis/thrombocytosis, staging certain neoplasms (lymphoma, mast cell tumors, multiple myeloma), and fever of unknown origin with hematologic abnormalities.
- Preferred sampling sites include the iliac crest, proximal humerus, proximal femur, or sternum in dogs, and the iliac crest or proximal femur in cats; Jamshidi-type needles are used for core biopsies, and standard spinal or bone marrow needles for aspiration.
- Sample handling is critical: aspirates require immediate smear preparation using Romanowsky-type stains (Wright-Giemsa, Diff-Quik), while core biopsies must be placed in 10% neutral buffered formalin for H&E staining, with special stains used as indicated.
- Key interpretive parameters include the myeloid to erythroid (M:E) ratio (normal range ~0.8:1 to 2.5:1), myeloid and erythroid maturation indices, megakaryocyte number and morphology, iron stores, and the presence of abnormal or neoplastic cells.
- Common pitfalls compromising diagnostic yield include hemodilution from peripheral blood contamination, inadequate smear preparation, decalcification artifacts in biopsies, and sampling errors from focal marrow lesions, necessitating careful technique and correlation with peripheral blood findings.
- Bone marrow aspiration is a valuable tool for detecting infectious agents like *Leishmania* species, with cell block processing of aspirates and immunohistochemistry demonstrating improved diagnostic sensitivity compared to conventional parasitologic methods.

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Bone marrow evaluation is a core diagnostic procedure in veterinary medicine, applied when peripheral blood abnormalities suggest primary or secondary marrow disease. This article provides a practical framework for the practicing veterinarian on when to sample, how to collect and handle specimens, and how to interpret the results in dogs and cats. It covers the procedural principles, sample preparation, cytologic and histologic interpretation, and common pitfalls that compromise diagnostic yield.

The clinical questions addressed are direct: Does this patient need a bone marrow evaluation? Which site and technique should be used? What do the findings mean for diagnosis, prognosis, and treatment planning? The article assumes familiarity with hematologic terminology and routine clinical pathology, and it focuses on decision criteria and interpretive logic instead of exhaustive cytologic descriptions of individual neoplasms.

## At a Glance

| Parameter | Recommendation or Fact |
|---|---|
| Primary indications | Unexplained cytopenia, bicytopenia, or pancytopenia, suspected marrow neoplasia, unexplained leukocytosis or thrombocytosis, staging for certain neoplasms, fever of unknown origin with hematologic abnormalities |
| Preferred sampling sites | Iliac crest, proximal humerus, proximal femur, or sternum in dogs, iliac crest or proximal femur in cats |
| Core needle selection | Jamshidi-type needle for core biopsy, standard spinal or bone marrow needle for aspiration |
| Sample handling | Prepare smears immediately from aspirate, place core biopsy in 10% neutral buffered formalin |
| Stains | Romanowsky-type stains (Wright-Giemsa, Diff-Quik) for cytology, H&E for histology, special stains as indicated |
| Key interpretive parameters | M:E ratio, myeloid and erythroid maturation indices, megakaryocyte number and morphology, iron stores, presence of abnormal cells |
| Common pitfalls | Hemodilution, inadequate smear preparation, decalcification artifacts in biopsy, sampling error from focal lesions |

## Physiologic Basis of Marrow Sampling

Bone marrow is the primary site of hematopoiesis in adult dogs and cats. The marrow compartment contains hematopoietic stem cells, progenitor cells, and maturing cells of the erythroid, myeloid, and megakaryocytic lineages, supported by a stromal microenvironment of fibroblasts, adipocytes, and endothelial cells. Understanding the normal maturation sequence is essential for interpreting cytologic and histologic specimens, because the diagnostic value of marrow evaluation depends on recognizing orderly maturation, appropriate lineage proportions, and the absence of foreign or neoplastic cells.

The expected number of thrombopoietic cells in normal canine marrow is poorly defined, and smear preparation technique significantly influences counts. A study comparing four smear types in clinically healthy Beagle dogs found that buffy coat smears yielded the highest mean total thrombopoietic cell counts at 8.05 cells per low-power field, while particle-squash smears yielded the lowest at 1.55 cells per low-power field. Core biopsies produced 5.31 cells per high-power field but frequently failed to provide interpretable specimens. These findings indicate that the method of smear preparation materially affects quantitative interpretation, and clinicians should interpret thrombopoietic cell numbers with the preparation technique in mind.

## Indications for Bone Marrow Evaluation

### Hematologic Indications

Bone marrow aspiration and biopsy are indicated when peripheral blood abnormalities cannot be explained by routine diagnostic evaluation. The most common triggers are persistent cytopenias, including anemia, leukopenia, thrombocytopenia, or combinations thereof. Unexplained bicytopenia or pancytopenia warrants marrow evaluation to distinguish between decreased production, ineffective hematopoiesis, and peripheral destruction or sequestration. Similarly, unexplained leukocytosis, erythrocytosis, or thrombocytosis may indicate a primary marrow disorder such as chronic myeloid leukemia or essential thrombocythemia.

The decision to sample should be guided by the severity and duration of the abnormality, the presence of concurrent clinical signs, and the results of initial testing including complete blood count, reticulocyte count, and serum biochemistry. A nonregenerative anemia with normal leukocyte and platelet counts may justify marrow evaluation if iron deficiency, chronic disease, and renal disease have been excluded. Persistent neutropenia or thrombocytopenia that does not respond to appropriate therapy is another indication.

### Nonhematologic Indications

Bone marrow evaluation is also used for staging purposes in animals with suspected or confirmed neoplasia, particularly lymphoma, mast cell tumors, and multiple myeloma. The marrow can be a site of metastatic disease or a primary site of hematopoietic neoplasia. In endemic regions, marrow aspiration is a valuable diagnostic tool for detecting infectious agents, particularly Leishmania species. The bone marrow is a good target for the detection of Leishmania in dogs, and aspiration is rapid and less invasive compared with biopsy procedures. Cell block processing of aspirates with immunohistochemistry has been shown to improve diagnostic sensitivity for Leishmania infection compared with conventional parasitologic methods, with one study detecting infection in 31.1% of dogs by immunohistochemistry versus 13.3% by culture and 8.9% by histopathology.

## Sampling Techniques

### Aspiration

Bone marrow aspiration is performed with a Jamshidi-type or similar needle designed to penetrate cortical bone. The iliac crest is the most commonly used site in dogs and cats, although the proximal humerus, proximal femur, and sternum are acceptable alternatives. The choice of site depends on patient size, body condition, and the suspected disease process. Sedation or general anesthesia is typically required, and aseptic technique is mandatory.

After the needle is seated in the marrow cavity, a syringe is attached and negative pressure is applied. The aspirate should be expelled immediately onto glass slides and smears prepared using a squash or pull technique. The quality of the smear is critical for cytologic interpretation. A study comparing diagnostic accuracy for canine osteosarcoma found that core aspirate cytology using a bone marrow biopsy needle allowed penetration of cortical bone and aspiration with a larger bore needle than fine-needle aspiration, but there was no significant difference in diagnostic accuracy between the two techniques. This suggests that the choice of needle may be less important than the quality of the sample and the experience of the interpreter.

### Core Biopsy

Core biopsy provides a histologic specimen that preserves marrow architecture, which is essential for assessing cellularity, fibrosis, and the distribution of neoplastic infiltrates. The biopsy is obtained with a Jamshidi needle or similar device, and the core is gently expelled into fixative. Decalcification is required before sectioning, and this process can affect antigenicity for immunohistochemistry. The pathologist should be informed of the clinical suspicion so that appropriate fixation and processing protocols can be selected.

Core biopsy is particularly valuable when aspiration yields a dry tap, which may occur with marrow fibrosis, aplasia, or densely packed neoplastic infiltrates. In such cases, the biopsy may provide diagnostic material when cytology cannot. However, core biopsies frequently fail to provide interpretable specimens, as noted in the thrombopoietic cell study, and the clinician should be prepared to repeat the procedure if the sample is inadequate.

## Sample Handling and Preparation

The diagnostic yield of bone marrow evaluation depends on sample quality as much as on collection technique. Aspirate material should be expelled gently onto glass slides and smeared immediately. Wedge smears, squash preparations, and line smears all preserve cellular morphology when performed with minimal pressure. Delayed smearing allows clotting, which traps cells and obscures cytologic detail. Ethylenediaminetetraacetic acid (EDTA) is the preferred anticoagulant for liquid aspirate material destined for cytology or flow cytometry. Heparin distorts nuclear chromatin and should be avoided for morphologic evaluation.

Core biopsy specimens require fixation in 10% neutral buffered formalin. Decalcification with formic acid or EDTA is needed before sectioning. The pathologist should be informed whether the sample is from a cortical or cancellous site, because normal cellularity differs between locations. Aspirate smears and core biopsies are complementary: smears provide superior cytologic detail of individual cells, while biopsies preserve architecture, allow assessment of stromal changes, fibrosis, and necrosis, and permit immunohistochemistry when needed.

The choice of smear preparation method influences cell counts. In clinically healthy dogs, total thrombopoietic cell counts varied significantly among four smear techniques, with buffy coat smears yielding the highest counts and particle-squash smears the lowest. This finding has practical implications: when serial marrow evaluations are performed to monitor disease or treatment response, the same smear technique should be used each time to allow meaningful comparison.

## Assessment Sequence and Cellularity

The systematic evaluation of a bone marrow sample follows a fixed sequence. First, assess adequacy at low magnification. A minimum of 10 to 20 intact marrow spicules or particles should be present on aspirate smears. Second, estimate overall cellularity relative to fat. Normal canine and feline marrow is approximately 50% cellular in the adult, with higher cellularity in young animals and lower in aged patients. Third, evaluate megakaryocyte number and morphology. Fourth, determine the myeloid to erythroid (M:E) ratio. Fifth, perform a 200 to 500 cell differential count at high magnification. Sixth, assess iron stores if indicated.

Cellularity estimation on aspirate smears is semiquantitative at best. Core biopsies allow more accurate assessment because they preserve the fat to cell ratio. A trephine core of 1 to 2 cm length provides adequate material for histologic evaluation. Fragmentation of the core, crush artifact, or sampling from a site previously irradiated or infiltrated by neoplasia can produce falsely low cellularity readings.

The M:E ratio in normal dogs and cats ranges from approximately 0.8:1 to 2.5:1. A ratio below 0.5:1 suggests erythroid hyperplasia or myeloid hypoplasia. A ratio above 4:1 suggests myeloid hyperplasia or erythroid hypoplasia. These interpretations require correlation with the peripheral blood count. A low M:E ratio with anemia and reticulocytosis supports regenerative anemia. The same ratio with nonregenerative anemia and no reticulocytes suggests ineffective erythropoiesis or early erythroid arrest.

## Decision Table for Sampling

| Clinical Scenario | Aspirate | Core Biopsy | Rationale |
|---|---|---|---|
| Unexplained nonregenerative anemia | Yes | If aspirate nondiagnostic | Differentiates hypoplasia from dysplasia or neoplasia |
| Persistent neutropenia or thrombocytopenia | Yes | If aspirate nondiagnostic or if fibrosis suspected | Detects myeloid hypoplasia, maturation arrest, or infiltration |
| Suspected hematopoietic neoplasia | Yes | Yes | Biopsy confirms architecture and allows immunophenotyping |
| Fever of unknown origin with cytopenias | Yes | If aspirate negative | Evaluates for infectious agents, histiocytic disease |
| Staging of known neoplasia | Yes | If marrow infiltration suspected | Confirms or excludes metastatic disease |
| Monitoring therapy response | Yes | Serial aspirates preferred | Less invasive, repeatable, same technique required |
| Suspected myelofibrosis or marrow necrosis | No | Yes | Aspirate often yields dry tap or hemodilute sample |
| Suspected osteosarcoma | Core aspirate cytology | Yes | Core aspirate cytology with ALP staining showed 95% diagnostic accuracy in one study |

The decision to sample the marrow should be guided by peripheral blood findings. Persistent cytopenia in more than one cell line, unexplained leukocytosis with left shift, circulating blast cells, or unexplained hypercalcemia all warrant marrow evaluation. The procedure is contraindicated in patients with severe coagulopathy unless the bleeding risk is addressed first.

## Interpretation of Myeloid and Erythroid Lineages

Myeloid hyperplasia with a left shift appears as increased proportions of promyelocytes and myelocytes. This finding accompanies inflammatory leukocytosis or recovery from neutropenia. Maturation arrest, where early precursors accumulate but mature neutrophils are scarce, suggests drug toxicity, immune-mediated destruction, or dysmyelopoiesis. Erythroid hyperplasia with normal maturation supports a regenerative response. Erythroid maturation arrest at the rubricyte stage occurs with iron deficiency, inflammatory disease, or drug exposure.

Megakaryocyte evaluation includes number, size, and nuclear morphology. Increased megakaryocytes with small hypolobulated forms suggest immune-mediated thrombocytopenia or accelerated platelet consumption. Decreased megakaryocytes with peripheral thrombocytopenia indicate reduced production. Megakaryocytic dysplasia with large bizarre forms raises concern for myeloid neoplasia.

Dysplastic changes in multiple cell lines, including nuclear cytoplasmic asynchrony, bizarre nuclear shapes, and abnormal granulation, support a diagnosis of myelodysplastic syndrome when persistent and unexplained by other causes. The [ASVCP quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) provide standards for laboratory evaluation and reporting that support consistent interpretation across serial samples.

## Infectious Disease Applications

Bone marrow aspiration is a valuable diagnostic tool for infectious diseases that localize in hematopoietic tissue. In dogs with suspected leishmaniosis, bone marrow aspiration is rapid and less invasive than biopsy, and the aspirate can be processed as a cell block for histopathology and immunohistochemistry. In one study of 45 dogs from an endemic area, immunohistochemistry on cell block preparations detected Leishmania spp. in 31.1% of dogs, compared with 13.3% by parasitologic culture and 8.9% by histopathology alone. This technique improves diagnostic sensitivity without requiring additional invasive sampling.

Serial marrow evaluation can monitor treatment response in infectious disease. In dogs treated for visceral leishmaniasis, clinical remission occurred during therapy, but amastigote forms persisted in marrow of five of seven dogs at the end of the study period. This finding illustrates that clinical response does not equate to parasitologic cure, and marrow evaluation provides a more accurate assessment of treatment efficacy.

## Species and Equipment Considerations

The choice between aspiration and core biopsy depends on the clinical question and available equipment. Aspiration requires only a needle, syringe, and glass slides, making it feasible in general practice. Core biopsy requires a trephine needle such as a Jamshidi or similar device, which may not be available in all settings. When only aspiration is possible, a dry tap or hemodilute sample should prompt referral for biopsy instead of abandonment of the evaluation.

Cats tolerate marrow aspiration well but require firm restraint or sedation. The proximal femur and humerus are common sites in cats, while the iliac crest is preferred in dogs. In very small patients, the wing of the ilium may yield limited material, and the proximal femur may be more productive. The sternum is an alternative site in dogs but carries a small risk of cardiac puncture if the needle is advanced too deeply.

The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific guidance on normal hematologic values and marrow findings that support interpretation across dogs, cats, and other species. When evaluating exotic or production animals, normal reference intervals and marrow cellularity expectations differ, and consultation with a clinical pathologist familiar with the species is advised.

## Complications and Failure Modes

Bone marrow sampling is generally safe, but complications do occur. Hemorrhage is the most common concern, particularly in thrombocytopenic patients. Mild bleeding at the site is expected and self-limiting. Significant hemorrhage is rare but more likely with core biopsy than aspiration, especially when the patient has a coagulopathy. Detect hemorrhage early by monitoring the site for swelling and by reassessing packed cell volume in the hours after sampling. Apply firm manual pressure for several minutes after needle removal.

Infection is uncommon but can follow sampling through contaminated skin or when aseptic technique is breached. Osteomyelitis may present days later with pain, fever, or draining tract. The risk is higher in immunocompromised patients. Use strict aseptic preparation and sterile gloves for all marrow procedures.

Fracture is a recognized complication of core biopsy, particularly at the proximal humerus or femur in small or osteoporotic patients. The iliac crest is the safest site in cats and small dogs. If the patient is fractious or the bone is unusually hard, stop and reconsider the approach instead of applying excessive force.

Nerve or vessel injury can occur with improper landmarking. The sciatic nerve lies caudal to the proximal femur, and the femoral vessels run medial to the shaft. Aspirating too far cranially or medially at the proximal femur risks both. Use palpable landmarks and direct the needle along the long axis of the bone.

Cardiorespiratory compromise is rare but can follow heavy sedation or anesthesia in already debilitated patients. Hypotension, bradycardia, or hypoventilation should be detected through routine monitoring during the procedure. Have reversal agents and emergency drugs drawn up before starting.

## Common Errors and Corrective Actions

The most frequent error is submitting inadequate material. A dry tap does not always mean marrow disease. It may reflect needle placement in the cortex, an empty medullary cavity, or a tightly packed marrow that resists aspiration. If the first attempt yields nothing, reposition the needle and try again. If the second attempt also fails, proceed to core biopsy.

Smear preparation errors are equally common. Thick smears obscure cellular detail and mimic increased cellularity. Thin smears may contain only peripheral blood. Prepare smears immediately after collection using a gentle squash technique. The feathered edge should be thin enough to read individual cell morphology.

Decalcification artefact is a problem when core biopsies are processed improperly. Over-decalcification destroys nuclear detail and makes lineage assessment impossible. Request that the laboratory minimize decalcification time or split the core for separate processing.

Contamination with peripheral blood is another frequent issue. Blood-diluted aspirates underestimate cellularity and distort myeloid to erythroid ratios. Recognize this by the presence of many mature erythrocytes with few nucleated cells. If the sample is hemodilute, repeat the aspiration or rely on the core biopsy for cellularity assessment.

Inexperienced clinicians often misinterpret the myeloid to erythroid ratio. A low ratio may reflect erythroid hyperplasia, myeloid hypoplasia, or peripheral blood contamination. Always correlate the ratio with overall cellularity and with the peripheral blood count. The ratio alone is never diagnostic.

## Troubleshooting Table

| Observation | Likely Cause | Discriminating Check |
| --- | --- | --- |
| Dry tap at first attempt | Needle in cortex, not medulla | Reposition needle, confirm intramedullary placement by feeling a give as the cortex is penetrated |
| Dry tap at second attempt | Packed marrow or empty medullary cavity | Proceed to core biopsy, compare with peripheral blood findings |
| Smear too thick | Excessive marrow on slide | Prepare new smear with less material, use squash technique |
| Smear too thin | Peripheral blood only | Look for fat droplets and marrow spicules, repeat aspiration if absent |
| Hemodilute sample | Blood contamination | Low nucleated cell count with high erythrocyte background, repeat or use core |
| Low cellularity on aspirate | Peripheral blood dilution or true hypocellularity | Compare with core biopsy cellularity |
| High cellularity on aspirate | True hypercellularity or thick smear | Check smear thickness, correlate with core biopsy |
| Poor nuclear detail | Delayed staining or old stain | Restain with fresh stain, ensure smears are fixed promptly |
| Decalcification artefact | Prolonged acid decalcification | Request reduced decalcification time or split core |

## Limitations of Current Evidence

The veterinary literature on bone marrow sampling has notable gaps. Studies are often small and use healthy research dogs instead of clinical patients. The expected number of thrombopoietic cells in normal canine marrow is poorly defined, and different smear preparation methods yield significantly different counts, as shown in a comparison of four smear techniques in healthy Beagles. This means that published reference values must be interpreted with caution and that each laboratory should establish its own internal reference ranges.

Diagnostic accuracy data for cytology of bone lesions are limited. One study comparing fine-needle aspiration with a novel core aspirate technique for canine osteosarcoma found no significant difference in diagnostic accuracy between the two methods, although both were highly accurate when combined with alkaline phosphatase staining. The study was small, and the results may not generalize to other tumor types or to non-neoplastic bone disease.

Expert opinion still differs on several points. Some clinicians prefer aspiration alone for most indications, while others advocate routine core biopsy because it preserves architecture and allows immunohistochemistry. The choice of site also remains debated, with some favouring the iliac crest and others the proximal humerus. Neither position is supported by strong comparative data.

The use of cell block techniques on aspirated material is promising but not yet standardized. One study found that cell block immunohistochemistry detected Leishmania infection in more dogs than parasitological culture or histopathology alone. This suggests that cell block preparation may improve diagnostic yield for infectious disease, but the technique requires validation across laboratories.

## Referral and Escalation

Referral to a specialist is warranted when sampling has failed repeatedly, when the patient is unstable, or when the suspected condition requires advanced diagnostics. A veterinary clinical pathologist should review any marrow sample when the clinician is uncertain about interpretation. Many commercial laboratories offer consultation services where a pathologist will review slides and discuss findings with the submitting clinician.

Specialist consultation is also appropriate when the differential diagnosis includes a condition with major therapeutic or prognostic implications, such as myeloid neoplasia or metastatic neoplasia. The American Society for Veterinary Clinical Pathology provides quality assurance and laboratory standards guidance that can help clinicians select appropriate laboratories and interpret their results.

Regulatory reporting may be required for certain infectious diseases. Leishmaniasis is reportable in many regions, and the World Organization for Animal Health maintains international standards for disease surveillance and control. Clinicians should be aware of local reporting requirements and should contact their regional veterinary authority when a reportable disease is confirmed or suspected.

Laboratory involvement should begin before sampling if there is any doubt about sample handling or test selection. Most laboratories provide collection instructions and can advise on the volume of material needed for flow cytometry, cytogenetics, or molecular testing. Early communication prevents the common problem of collecting insufficient material for the tests that ultimately prove necessary.

## Frequently Asked Questions

### What is the minimum sample quality needed before I can trust a negative bone marrow result?

A negative result is only reliable if the sample contains adequate hematopoietic tissue. For aspirate smears, require at least 300 to 500 intact cells per high-power field across multiple fields, with identifiable megakaryocytes and no more than minimal peripheral blood dilution. For core biopsies, the specimen must contain at least 5 to 10 interpretable marrow spaces, also cortical bone or blood clot. If the sample fails these criteria, report it as nondiagnostic and repeat the procedure. The [American Society for Veterinary Clinical Pathology guidelines](https://www.asvcp.org/page/QALS_Guidelines) emphasize that sample quality directly determines whether cytologic interpretation is valid, and a nondiagnostic sample should never be used to rule out marrow disease.

### How do I proceed when a core biopsy needle is unavailable?

Aspiration alone can answer most clinical questions, particularly for diffuse processes such as immune-mediated cytopenias, staging of lymphoma, or evaluation of overall cellularity. If a core biopsy is needed but unavailable, consider a surgical wedge biopsy under general anesthesia, or collect a larger aspirate volume and prepare buffy coat smears to concentrate cells. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) describes aspiration as the primary sampling method for most marrow disorders, with core biopsy reserved for suspected myelofibrosis, marrow necrosis, or metastatic neoplasia. When you cannot obtain a core, document the limitation in the record and interpret negative findings with appropriate caution.

### What should I document in the medical record after marrow sampling?

Record the indication, sampling site, needle gauge and type, number of aspirate smears and core sections, whether the procedure was ultrasound-guided or blind, and any complications such as hemorrhage or failed attempts. Describe sample quality at collection, including whether particles were present and whether the core was intact. Note the person who performed the procedure and the laboratory receiving the samples. The [AVMA practice resources](https://www.avma.org/resources-tools) advise that procedure notes should support medical decision-making and continuity of care, so include the preliminary cytologic impression if one was made. This documentation also matters for serial evaluations, where comparing cellularity and lineage proportions across time requires knowing exactly how each sample was obtained.

### How does the approach differ in cats compared with dogs?

Cats have smaller marrow spaces and a higher proportion of adipose tissue, so aspirates yield fewer particles and cellularity estimates are more challenging. Use a 22-gauge needle in cats, and consider the humerus or femur instead of the ilium, as the feline ilium is thin and fractures more easily. Cats also have a higher incidence of marrow suppression secondary to feline leukemia virus, so additional testing such as FeLV antigen and FIV antibody testing should accompany marrow evaluation when cytopenias are present. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) notes that feline marrow is more prone to hemodilution, and buffy coat preparation may improve diagnostic yield. Core biopsy in cats requires a smaller needle and greater care to avoid penetrating the far cortex.

### When is it reasonable to refer a case for bone marrow evaluation instead of sampling in general practice?

Refer when the patient is unstable, when you lack experience with the technique, or when the suspected disease requires specialized ancillary testing such as flow cytometry, cytogenetics, or immunohistochemistry that your laboratory cannot perform. Refer also when the patient has severe thrombocytopenia with a high bleeding risk, as the procedure may require platelet transfusion support that is not available in your setting. The [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) apply to reportable infectious diseases, and if leishmaniosis or other regional pathogens are suspected, referral to a center with appropriate diagnostic capacity may be prudent. A failed first attempt with a nondiagnostic sample is another indication for referral instead of repeated blind sampling.

### How do I explain the procedure and its limitations to a client who is anxious about cost and risk?

Explain that bone marrow sampling is a minor procedure performed under sedation or brief anesthesia, with the main risks being mild bleeding or bruising at the site. Be direct about cost: the procedure itself is modest, but the laboratory interpretation, special stains, and culture or PCR add substantially. State clearly that the sample may occasionally be nondilute or nondiagnostic, requiring a repeat procedure. The [ASVCP quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) support the principle that clients should understand the diagnostic plan and its limitations before consent. Offer a staged approach, starting with less expensive tests such as complete blood count and serum chemistry, and proceed to marrow sampling only if those results justify it.

## Related Clinical & Scientific Guides

* [Peripheral Blood Smear Evaluation: A Step-by-Step Guide](/knowledge/veterinary-medicine/clinical-pathology/peripheral-blood-smear-evaluation-guide)
* [Reticulocyte Counts in Veterinary Medicine: Clinical Utility and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/reticulocyte-counts-veterinary-medicine)
* [Cerebrospinal Fluid Analysis in Veterinary Neurology: Collection and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/cerebrospinal-fluid-analysis-veterinary)


## References and Further Reading

- [A novel method of core aspirate cytology compared to fine-needle aspiration for diagnosing canine osteosarcoma.](https://pubmed.ncbi.nlm.nih.gov/21852507/). 2011.
- [Type of smear may influence thrombopoietic cell counts in the bone marrow of clinically healthy dogs.](https://pubmed.ncbi.nlm.nih.gov/16270260/). 2005.
- [The canine epiphyseal-derived mesenchymal stem cells are comparable to bone marrow derived-mesenchymal stem cells.](https://pubmed.ncbi.nlm.nih.gov/25391394/). 2015.
- [Cell-block Immunohistochemistry of Bone Marrow Aspirates: a Novel Tool to Improve the Diagnosis of Leishmania Infection in Dogs.](https://pubmed.ncbi.nlm.nih.gov/26852343/). 2016.
- [Clinical and parasitological evaluation of dogs naturally infected by Leishmania (Leishmania) chagasi submitted to treatment with meglumine antimoniate.](https://pubmed.ncbi.nlm.nih.gov/16996214/). 2007.
- [Participation of ticks in the infectious cycle of canine visceral leishmaniasis, in Teresina, Piauí, Brazil.](https://pubmed.ncbi.nlm.nih.gov/25076429/). 2014.
- [American Society for Veterinary Clinical Pathology Guidelines](https://www.asvcp.org/page/QALS_Guidelines). American Society for Veterinary Clinical Pathology.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.

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- [Serial Bone Marrow Evaluation for Monitoring Myeloid Neoplasia](/knowledge/veterinary-medicine/clinical-pathology/serial-bone-marrow-evaluation-monitoring-myeloid-neoplasia)
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> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.