Which of the following is a correct pairing described in the notes?

• A. Cytocentrifuge speed — 200-1000 rpm; Best specimen for osmolality — Plasma
• B. Cytocentrifuge speed — 100-1000 rpm; Best specimen for osmolality — Serum
• C. Cytocentrifuge speed — 200-1000 rpm; Best specimen for osmolality — Serum
• D. Cytocentrifuge speed — 200-100 rpm; Best specimen for osmolality — Serum

Answer: (C)

Cytocentrifugation needs enough force to collect cells onto the slide without distorting or damaging them. A moderate range like 200–1000 rpm provides a good balance: it concentrates cells into a clean monolayer suitable for morphology assessment without excessive shear that could smear or lyse cells. Going outside this range can yield slides that are either poorly deposited or overhandled and degraded.

For osmolality testing, the specimen should reflect the true solute concentration without interference from additives. Serum is preferred because it comes from blood after clotting and removes cellular components and most anticoagulants, which can alter osmolar measurements. Anticoagulants in plasma can introduce substances that change osmolality readings, making the results less consistent.

So, the combination of cytocentrifuge speed in that 200–1000 rpm range with serum as the osmolality specimen aligns with these practical considerations, yielding reliable slides for cytology and trustworthy osmolality measurements.