What do burr cells (echinocytes) and large platelets on a peripheral blood smear indicate?

Burr Cells and Large Platelets: Clinical Significance

Burr cells (echinocytes) on a peripheral blood smear warrant immediate evaluation to exclude life-threatening thrombotic microangiopathy, while large platelets may indicate inherited platelet disorders, increased platelet turnover, or represent an artifact from specimen handling. 1

Burr Cells (Echinocytes): Diagnostic Approach

Immediate Priority: Exclude Artifact

• Echinocytes may arise from delayed specimen processing or improper storage; therefore a fresh peripheral-smear examination is essential to distinguish artifact from true pathology. 1
• True pathologic echinocytes persist on fresh smears and correlate with clinical findings. 1
• Do not dismiss echinocytes as artifact without confirming on a fresh specimen and correlating with the patient's clinical picture. 1

Critical Urgent Differential: Thrombotic Microangiopathy

• Thrombotic microangiopathy (TMA) must be urgently excluded; it is defined by the triad of non-immune microangiopathic hemolysis, thrombocytopenia, and organ involvement (most often renal). 1
• When TMA is suspected, order ADAMTS13 activity and inhibitor titer, a complete blood count with platelet count, LDH, direct antiglobulin test, peripheral-smear review, serum creatinine, and urinalysis without delay. 1
• Do not overlook TMA based solely on the presence of rare schistocytes; low schistocyte counts can occur early in disease evolution. 1
• If ADAMTS13 activity is < 10%, initiate therapeutic plasma exchange and methylprednisolone 1 g IV daily for 3 days immediately. 1
• Do not delay plasma exchange while awaiting ADAMTS13 results if clinical suspicion for TTP is strong. 1

Hemolytic Anemia Evaluation

• Assess hemolysis with LDH, haptoglobin, indirect bilirubin, and a direct antiglobulin test. 1
• The reticulocyte count is useful for estimating red cell production and determining whether the bone marrow is responding appropriately to anemia. 2
• In pyruvate kinase deficiency, the reticulocyte count may be inappropriately low relative to the degree of hemolysis because the spleen sequesters young red cells. 1

Pyruvate Kinase Deficiency

• Echinocytes are present in 3%–30% of patients with pyruvate-kinase (PK) deficiency, especially after splenectomy, making them a characteristic morphologic clue. 1
• In PK deficiency the peripheral smear typically shows anisocytosis, poikilocytosis, and variable echinocyte proportions together with laboratory evidence of chronic hemolysis (elevated reticulocyte count, LDH, indirect bilirubin; low haptoglobin). 1
• Diagnosis of PK deficiency requires demonstration of reduced PK enzyme activity and/or identification of pathogenic PKLR gene mutations. 1
• If hemolysis is confirmed without an immune cause, perform PK enzyme activity testing and consider PKLR gene-mutation analysis. 1

Other Causes

• Alcohol-induced echinocytosis can occur with chronic alcoholic liver disease, characterized by alterations in phosphatidylserine and phosphatidylinositol concentrations in the erythrocyte membrane. 3
• Physical examination for infection should specifically assess fever, tachycardia, hypotension, and identify a potential source. 1

Large Platelets: Diagnostic Considerations

Initial Assessment

• The peripheral blood smear permits interpretation of diagnostically significant findings including assessment of platelet size, morphology, and number. 4, 5
• Initial work-up includes a complete blood count with differential, reticulocyte count, and a careful peripheral-smear review performed by an experienced pathologist. 1

Inherited Platelet Disorders

• Hereditary giant platelet syndromes produce abnormally large platelets that can be two times larger than normal, particularly when platelets undergo shape change. 6
• In Montreal platelet syndrome (MPS), discocytes are normal sized; however, sphero-echinocytes and disco-echinocytes have mean volumes approximately two times larger than normal. 6
• Shape-changing agents (ADP, thrombin, cold incubation) produce abnormally large platelets in hereditary giant platelet syndromes, suggesting a defect in the mechanism regulating platelet size during shape change. 6

Increased Platelet Turnover

• Large platelets may indicate increased platelet production in response to peripheral destruction or consumption, reflecting younger, larger platelets released from the bone marrow. 4
• The presence of large platelets should prompt evaluation of the platelet count and assessment for thrombocytopenia or thrombocytosis. 4

Myelodysplastic Syndromes

• If a primary bone-marrow disorder is suspected, obtain bone-marrow aspiration/biopsy with cytogenetics and flow cytometry; conventional cytogenetic analysis is used to detect clonal abnormalities. 1
• Bone marrow aspiration with Prussian blue stain for iron and biopsy are needed to evaluate the degree of hematopoietic cell maturation abnormalities and relative proportions, percentage of marrow blasts, marrow cellularity, presence or absence of ringed sideroblasts, and fibrosis. 7

Laboratory Work-Up Algorithm

1. Obtain a fresh peripheral blood smear immediately to confirm true echinocytes versus artifact. 1
2. Complete blood count with differential, reticulocyte count, and platelet count. 1, 2
3. Hemolysis panel: LDH, haptoglobin, indirect bilirubin, direct antiglobulin test. 1
4. If TMA suspected: ADAMTS13 activity, serum creatinine, urinalysis, complement studies (C3, C4, CH50). 1
5. If hemolysis confirmed without immune cause: PK enzyme activity and PKLR gene analysis. 1
6. Comprehensive metabolic panel to evaluate renal and hepatic status. 1