Success! In Clinical Laboratory Science – Hemostasis Practice Test

The correct platelet count expressed in SI units is

178 * 109/L 178 * 103/L 356 * 109/cu. mm 712,000 * 109/L

Correct Answer:

178 * 109/L

Explanation:

Platelet count in SI units is expressed as the number of platelets per liter (per liter is the SI base for such counts). The normal way to write this is in billions per liter, i.e., ×10^9/L. So a count of 178 × 10^9/L means about 178 billion platelets per liter, which fits the typical adult reference range of roughly 150–450 × 10^9/L (equivalent to about 150,000–450,000 platelets per microliter). The other formats don’t align with SI conventions or the usual magnitudes: using ×10^3/L would give 178,000 per liter, far too low; expressing per cubic millimeter with ×10^9 would misstate the scale (1 μL = 1 mm^3, so the typical per-μL value would be about ×10^3/μL, not ×10^9/μL); and an enormous figure like 712,000 × 10^9/L is not plausible for a human blood count.

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