Low Automated Platelet Count With NRBCs: Resolving Pseudothrombocytopenia and WBC Interference
27-year-old man has a routine pre-employment CBC. Analyzer results: WBC 13.2 × 10^9/L, RBC 4.80 × 10^12/L, Hb 14.5 g/dL, Hct 42.5%, MCV 88.5 fL, and platelets 41 × 10^9/L. He has no bruising, bleeding, fever, or hepatosplenomegaly, and no medications. The automated analyzer flags “platelet clumps” and “NRBC present.” The manual differential shows 8 nucleated RBCs per 100 WBCs and adequate single platelets with several large platelet clumps near the feathered edge. The WBC histogram shows a shoulder in the 200–250 fL region. The laboratory is asked how to report the WBC and platelet counts and what quality steps are required.
1. Calculate the NRBC-corrected WBC count and explain why the uncorrected count is misleading.
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Corrected WBC = uncorrected WBC × 100 / (100 + NRBC per 100 WBC) = 13.2 × 100 / 108 = 12.2 × 10^9/L. The analyzer counts nucleated RBCs as white cells because both generate nuclei-related signals; the shoulder in the 200–250 fL region is consistent with NRBC interference. Reporting 13.2 × 10^9/L would overstate the true leukocyte count and could suggest leukocytosis when the corrected count is only mildly elevated. The report should include the corrected WBC and note the NRBC count. This correction matters most when the NRBC count is high; even 8 NRBCs per 100 WBCs changes the result by about 1 × 10^9/L, which can affect clinical interpretation.
2. How should the platelet count be resolved, and what should be reported?
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The smear shows platelet clumps and adequate single platelets, so the analyzer count of 41 × 10^9/L is likely falsely low due to EDTA-dependent pseudothrombocytopenia. The first step is to repeat the count in a citrate tube, because citrate often prevents the antibody-mediated clumping; a heparin tube may be used if citrate also fails, but heparin can cause its own platelet clumping. If a citrate tube is used, remember the dilutional effect and either correct for it or report the result as citrate-anticoagulated with a comment. A manual estimate from the smear can support the finding but should not replace a reliable count. Report the platelet count with a comment that the initial EDTA specimen showed clumping and that the repeat method was used. Do not report 41 × 10^9/L as a true platelet count without this evaluation.
3. What quality and instrument troubleshooting steps are indicated?
Read the worked answer
Review the analyzer flags, check the specimen for clots or short draw, and repeat the CBC on a fresh specimen. Confirm the NRBC flag by manual differential and apply the WBC correction. For platelets, examine the feathered edge for clumps and repeat in an alternate anticoagulant. Document the discrepancy, the corrective action, and the final reported result. Isolated pseudothrombocytopenia does not require analyzer recalibration, but repeated failures or discrepant flags should trigger service checks and review of the platelet histogram and flagging thresholds. Communicate with the clinician that the low platelet count is likely spurious and that the patient is not thrombocytopenic. The key quality judgment is to prevent a false diagnosis of thrombocytopenia while still reporting the NRBC-corrected WBC accurately.