RBC values are usually given in what units?

• A. Millions per microliter
• B. Millions per milliliter
• C. Thousands per microliter
• D. Thousands per milliliter

Answer: (A)

RBC values are reported as millions per microliter because red blood cells are incredibly numerous in a tiny volume of blood, so the most practical and commonly used scale is to express the count as millions per microliter. A typical range is around 4 to 6 million cells in each microliter of blood, which keeps the numbers easy to interpret. Using millions per milliliter would make the figures billions per milliliter (since 1 milliliter contains 1000 microliters), which is less convenient. Expressing as thousands per microliter would understate the count by about three orders of magnitude. For contrast, white blood cells and platelets are usually counted in thousands per microliter, reflecting their much lower numbers.