Required section · Section 3 of 6

Patterns, interferences, and local review rules

A low-volume shift has events left of the usual RBC-volume distribution and can accompany small RBCs or fragments; a high-volume shift has events rightward and can accompany large RBCs, reticulocytes, or RBC agglutinates. Broadening is increased distribution width and is reflected by RDW-CV and/or RDW-SD; a shoulder is an asymmetric extension rather than proof of a second group. A true dual population is two separable event-density peaks and may accompany mixed RBC populations. Each shape has analytical as well as biological possibilities: compare MCV/RDW, inspect plot quality and specimen, and review a peripheral smear for microcytes, macrocytes, fragments, dimorphism, or agglutination before naming a cause.

Platelet clumps create a full interference path: EDTA-dependent aggregation forms particles outside the platelet counting region, producing a spuriously low automated platelet count; large clumps may also affect the WBC count. When a low platelet result, platelet-distribution abnormality, or platelet-clump flag meets the validated local criterion, inspect the tube and a fresh smear for clumps, then recollect in an approved alternate anticoagulant or use a validated alternate platelet method. Review result consistency and report only the result/comment authorized by that procedure; escalate unresolved interference.

Cold-reactive RBC agglutination creates another path: RBC clumps can be counted as fewer, larger events, causing low RBC count and hematocrit with high MCV, MCH, and MCHC. Confirm agglutination on smear, follow the validated warming/reanalysis procedure, review consistency, and release only the authorized corrected result/comment or escalate. Lipemia creates a different path: turbidity can increase photometric hemoglobin, yielding high hemoglobin, MCH, and MCHC with a hemoglobin/hematocrit discrepancy. Inspect plasma, apply the laboratory's validated lipemia procedure, verify the resolved measurement against CBC consistency, and report or escalate only under that procedure. Trace each discordance from interference to affected measurement to confirmation, correction, reportability, and escalation.

Interference pathways: observed evidence, mechanism, smear/specimen correlation, and validated local outcome
Observed clue	Possible analytical explanation	Correlate before action	Bounded action
Broad RBC curve or shoulder	Mixed RBC volumes, fragments, reticulocytes, or agglutination alter an impedance-volume distribution	RBC indices, tube appearance, and smear morphology	If local smear criterion is met, review and document morphology; do not diagnose from the curve
Low PLT with high-volume tail or clump flag	EDTA platelet clumps fall outside platelet region; large clumps can also affect WBC	Tube inspection and fresh smear labeled for platelet clumps	Validated clump rule: suppress/review as required, recollect approved alternate anticoagulant or use validated alternate method
Low RBC/Hct with high MCV, MCH, MCHC	Cold-reactive RBC agglutination forms fewer, larger measured particles	Smear for RBC agglutination and local temperature history	Validated cold-agglutinin procedure: warm/reanalyze or escalate; release only authorized result/comment
High Hgb, MCH, MCHC with Hgb/Hct discrepancy	Lipemia can positively interfere with photometric hemoglobin	Inspect plasma for turbidity and review specimen history	Validated lipemia procedure: resolve interference or obtain authorized alternate result before release
WDF abnormality with NRBC-related flag	WDF classification concern; WNR separately enumerates WBC and NRBC	WNR reporting status and labeled smear evidence	Validated NRBC rule: perform smear review; do not manually correct an already WNR-corrected WBC

Knowledge checks

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Knowledge check 1

Low platelets plus a high-volume platelet tail meet the laboratory’s validated platelet-clump review criterion. Which outcome is appropriate?

Choose one option.

Inspect the tube and fresh smear for clumps, then use the approved alternate-anticoagulant recollection or validated alternate platelet method.

Release thrombocytopenia from the automated platelet result alone.

Apply a manual NRBC correction to resolve the platelet pattern.

Knowledge check 2

Visible turbidity accompanies high hemoglobin, MCH, and MCHC with a hemoglobin/hematocrit discrepancy. Which action follows the likely interference path?

Choose one option.

Inspect plasma and apply the validated lipemia procedure before releasing a photometrically affected hemoglobin result.

Use the RBC histogram alone to diagnose the cause of the turbidity.

Apply a manual NRBC correction to the WBC.

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