A fibrinogen assay is performed on the coagulation analyzer using the standard 1:10 dilution with Owren's buffer. The seconds obtained do not read on the standard curve. An alternate 1:20 dilution is performed and is 400 mg/dL when read off the curve. The concentration of fibrinogen to be reported in mg/dL is

• A. 160 mg/dL
• B. 200 mg/dL
• C. 400 mg/dL
• D. 800 mg/dL

Answer: (D)

The test result must be translated back to the original, undiluted sample by adjusting for the dilution factor. Using a 1:20 dilution means the sample is twice as dilute as the standard 1:10 dilution (20 is twice 10). The curve readout of 400 mg/dL corresponds to the diluted sample, so to estimate the fibrinogen in the original sample you multiply by the ratio of the dilutions: 20/10 = 2. Therefore, 400 mg/dL × 2 = 800 mg/dL.