What two types of variation are accounted for in the RCV calculation?

• A. Inter-individual variation and sampling error
• B. Intra-individual biological variation and analytical variation/imprecision
• C. Analytical calibration drift and instrument variance
• D. Population variability and random error

Answer: (B)

RCV is about determining whether a change in a patient’s repeated lab result is truly meaningful or just normal fluctuation. The two factors it incorporates are the natural fluctuation of the analyte within the same person over time (intra-individual biological variation) and the imprecision of the measurement itself (analytical variation). Together these define how much a repeated result can vary by chance; only changes exceeding this combined variability are considered clinically significant.

Inter-individual (population) variability describes differences between different people, not how a single patient’s value changes over time, so it isn’t used to judge within-patient change. Analytical drift or instrument variance are aspects that contribute to analytical variation, but the established framing emphasizes intra-individual biological variation plus analytical variation/imprecision.