Key Formulas

Question 1

What is the formula to calculate Mean Corpuscular Volume (MCV)?

Answer 1

MCV = (HCT / RBC) × 1000

Question 2

What is the formula to calculate Mean Corpuscular Hemoglobin (MCH)?

Answer 2

MCH = HGB / RBC

Question 3

What is the formula to calculate Mean Corpuscular Hemoglobin Concentration (MCHC)?

Answer 3

MCHC = HGB / HCT

Question 4

How do you calculate the Corrected Reticulocyte Count (for anemia)?

Answer 4

Corrected Reticulocyte % = Reticulocyte % × (Patient’s HCT / Normal HCT)
Normal HCT is typically 45% for men, 40% for women.

Question 5

Why is the reticulocyte count corrected, and what does the correction account for?

Answer 5

In specimens with a low hematocrit, the percentage of reticulocytes may be falsely elevated because the whole blood contains fewer RBCs. A correction factor is used, with the average normal hematocrit considered to be 45%.

Question 6

How do you calculate the Corrected White Blood Cell (WBC) Count when nucleated red blood cells (nRBCs) are present on a smear?

Answer 6

Corrected WBC Count = Observed WBC Count × [100 / (nRBCs + 100)]
nRBCs = number of nucleated RBCs per 100 WBCs.

Question 7

Why must the WBC count be corrected when nRBCs are present?

Answer 7

Automated cell counters count nucleated RBCs as white blood cells, falsely elevating the WBC count. This correction removes them from the total.

Question 8

What is the “Rule of Three” or “H&H Check” in a CBC?

Answer 8

A quick visual check that, under normal conditions, the Hematocrit (HCT) value should be approximately three times the Hemoglobin (HGB) value (within a margin of ±3).
Formula: 3 x Hgb = HCT (± 0.03)

Question 9

If a patient’s hemoglobin (Hgb) is 150 g/L, what is the expected range for their hematocrit (HCT) using the Rule of Three formula?

Answer 9

Expected HCT range: 0.42 to 0.48 L/L

Question 10

What is the cell count formula when doing it manually?

Answer 10

(cells counted)(dilution factor)/(area counted)(depth)