Patterns that point to an interference

Cold-reactive IgM can agglutinate red cells below body temperature. On a method-specific histogram this can produce an irregular, broadened, high-volume aggregate pattern rather than a reliable cell-volume distribution. Aggregates may be counted as fewer, larger particles: RBC count and hematocrit fall while MCV, MCH, and especially MCHC rise; lysed-sample hemoglobin is comparatively reliable. Confirm with visible RBC agglutination on the original smear and apply a locally validated warmed rerun or warm recollection pathway.

Lipemic plasma is a turbidity-related photometric hemoglobin bias: inspect for lipemia, review the hemoglobin channel and internal relationships, and use a validated alternate hemoglobin approach or hold/escalate if it remains unresolved. Cell-free hemoglobin can also raise the photometric hemoglobin result, but requires separate evidence of free hemoglobin and a specimen/context review; a plasma observation alone does not establish its source. RBC destruction can occur in vitro or in vivo and is a separate process that can reduce intact RBC count and hematocrit; inspect specimen appearance, smear, collection history, and clinical context, then recollect or escalate when the destruction pathway cannot be resolved.

EDTA-dependent clumping makes the platelet count unreliable but does not exclude true thrombocytopenia. Confirm clumps on the original smear. Giant platelets can be undercounted above an impedance gate, while fragments or microcytes can be overcounted inside it; use direct morphology and an available validated alternate method to determine the reportable result.

For a short-filled K2EDTA tube, first confirm fill and specimen integrity, then review for relative anticoagulant excess (including reduced MCV, increased MCHC, and distorted morphology), inspect the original smear, and obtain a suitable recollection when the locally validated reportability limit is not met. For extreme leukocytosis, review analyzer linearity, flags, platelet separation, specimen, and original smear; use the validated dilution or alternate method, determine whether the analyzer or laboratory information system has already corrected the diluted rerun, compare evidence, then release only a verified result or suppress, recollect, consult, or escalate.