Laboratory Mathematics and Calculations Flashcards

A serum sample is diluted 1:5, and that dilution is then diluted 1:10. What is the final dilution?

Answer: 1:50

For serial dilutions, multiply the individual dilution factors: 5 × 10 = 50, so the final dilution is 1:50.

How many grams of NaCl (molecular weight 58.5 g/mol) are needed to prepare 1 L of a 0.5 M solution?

Answer: 29.25 g

Grams = molarity × MW × volume (L) = 0.5 × 58.5 × 1 = 29.25 g.

A 100 mg/dL standard has an absorbance of 0.200. An unknown run under the same conditions has an absorbance of 0.400. What is the unknown's concentration?

Answer: 200 mg/dL

By Beer's law, Cu = (Au / As) × Cs = (0.400 / 0.200) × 100 = 200 mg/dL.

In a manual WBC count, 200 cells are counted in the 4 large corner squares (each 1 mm², depth 0.1 mm) of a hemocytometer. The dilution is 1:20. What is the WBC count?

Answer: 10,000/µL

Cells/µL = (cells counted × dilution factor) / (area counted × depth) = (200 × 20) / (4 × 0.1) = 4,000 / 0.4 = 10,000/µL.

A control has a mean of 100 mg/dL and a standard deviation of 4 mg/dL. What is the coefficient of variation (CV)?

Answer: 4%

CV = (SD / mean) × 100 = (4 / 100) × 100 = 4%.

A glucose result is 90 mg/dL. Glucose has a molecular weight of 180 g/mol. What is the result in mmol/L?

Answer: 5.0 mmol/L

mmol/L = (mg/dL × 10) / MW = (90 × 10) / 180 = 5.0 mmol/L. The factor of 10 converts deciliters to liters.