Required section · Section 5 of 6

Your call: classify, correlate, and decide

Identify the cells you can identify, judge whether the preparation supports that identification, and decide what the pattern means when correlated with the other results. Separate confident calls from cells that need a second review.

Refer a slide to a qualified reviewer when it shows a monomorphic population, a high nuclear-to-cytoplasmic ratio, fine chromatin, or prominent nucleoli. Reactive lymphocytes can partly mimic these features. A neutrophil-predominant inflammatory pattern alone, even at 62 percent, does not trigger referral. The laboratory sets reviewer qualifications, reflex flow cytometry or cytology criteria, and critical-value notification rules; do not rely on a universal numeric threshold.

Timing also matters for hemorrhage-related findings. RBCs, erythrophagocytosis, and siderophages do not all appear at once; they represent a sequence from fresh blood exposure through red-cell ingestion to iron breakdown. Use that sequence without assigning an exact hour, because the timing varies too much for any of these findings to serve as a precise clock.

Match the finding to the action it actually supports, correlate before you commit to a pattern name, and reserve referral for the specific features that call for it.

Decision card showing five CSF pattern categories, neutrophilic, lymphocytic, mixed, eosinophilic, and macrophage-rich, all feeding into a correlation step, then into a coral referral box describing a monomorphic blast-like population as the trigger for qualified reviewer referral, with a note that reactive lymphocytes can resemble blasts. — Figure 1Five CSF differential patterns, the correlation step, and the specific referral trigger.

Ordering exercise

A CSF specimen contains blood from an in vivo hemorrhage that occurred before the tap. Place these three findings in the sequence they are expected to appear over time, from earliest to latest.

1. Siderophages

Macrophages contain hemosiderin from breaking down ingested RBCs, supporting prior blood breakdown; onset and persistence vary too much to date the bleed precisely from this finding alone.
2. Intact RBCs with an otherwise unremarkable differential

Fresh blood is present in the CSF; at this point the RBCs are simply visible, not yet ingested or broken down by macrophages.
3. Erythrophagocytosis

Macrophages are seen with ingested intact or partially digested RBCs; this does not occur when blood and CSF are simply mixed outside the body, so it favors bleeding before collection.

Knowledge checks

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Knowledge check 1

Given the guided case (neutrophil-predominant differential, mild degeneration flag, no blast-like population), what is the defensible next laboratory action?

Choose one option.

Release the validated results with the preparation limitation noted, and follow local critical-value and reviewer policy

Withhold the result until degeneration clears on a repeat cytospin

Independently report a diagnosis of bacterial meningitis

Discard the differential and report only the automated count

Knowledge check 2

Which features should trigger referral to a qualified reviewer rather than routine reporting? Select all that apply.

Choose at least 2 options.

A monomorphic population with a high nuclear-to-cytoplasmic ratio, fine chromatin, and prominent nucleoli

Difficulty distinguishing a reactive lymphocyte from a blast-like cell on morphology alone

A neutrophil-predominant differential in an acutely inflamed specimen

An entirely lymphocyte and monocyte differential with no other atypical features

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