A cytospin lands on the bench at 09:35

A lumbar CSF specimen is collected at 09:10, received in the laboratory at 09:22, and cytospun at 09:35. It is clear and colorless, so nothing about its appearance predicts what the differential will show. The validated hemocytometer count already flags a problem: total nucleated cells (TNC) are 42 cells/uL against this case laboratory's validated adult interval of 0 to 5 cells/uL, and red blood cells (RBC) are 18 cells/uL against this case laboratory's validated adult interval of 0 to 5 cells/uL. Protein is 78 mg/dL against a local adult range of 15 to 45 mg/dL, and glucose is 43 mg/dL with a simultaneous serum glucose of 92 mg/dL, a CSF to serum ratio of 0.47. The RBC elevation is considered separately: collection contamination, including a traumatic tap, and hemorrhage remain possibilities and are not established by this count alone.

The cytospin itself carries a slide flag: mild degeneration, interpretation limited. That flag matters before a single cell is named. CSF leukocytes deteriorate quickly once collected, and a slide prepared at 25 minutes will show cleaner morphology than one prepared after 90 or 150 minutes. Decide both what pattern the differential supports and whether the slide is good enough to trust the answer.

On Wright-Giemsa stain, 100 intact leukocytes are counted: neutrophils 62 percent, lymphocytes 25 percent, monocytes 10 percent, macrophages 3 percent, eosinophils 0 percent. No erythrophagocytosis, siderophages, plasma-cell clusters, lining-cell groups, microorganisms, or blast-like population is seen. Gram stain is pending, and bacterial culture and a nucleic-acid test are ordered.

A differential is only as trustworthy as the preparation it came from, so read the slide-quality flag before you read the percentages.