Clinical decision limits as criteria for setting analytical performance specifications for laboratory tests.

BACKGROUND

The biological (CV), preanalytical (CV), and analytical variation (CV) are inherent to clinical laboratory testing and consequently, interpretation of clinical test results.

METHODS

The sum of the CV, CV, and CV, called diagnostic variation (CV), was used to derive clinically acceptable analytical performance specifications (CAAPS) for clinical chemistry measurands. The reference change concept was applied to clinically significant differences (CD) between two measurements, with the formula CD = z*√2* CV. CD for six measurands were sought from international guidelines. The CAAPS were calculated by subtracting variances of CV and CV from CV. Modified formulae were applied to consider statistical power (1-β) and repeated measurements.

RESULTS

The obtained CAAPS were 44.9% for urine albumin, 0.6% for plasma sodium, 22.9% for plasma pancreatic amylase, and 8.0% for plasma creatinine (z = 3, α = 2.5%, 1-β = 85%). For blood HbA and plasma low-density lipoprotein cholesterol, replicate measurements were necessary to reach CAAPS for patient monitoring. The derived CAAPS were compared with analytical performance specifications, APS, based on biological variation.

CONCLUSIONS

The CAAPS models pose a new tool for assessing APS in a clinical laboratory. Their usability depends on the relevance of CD limits, required statistical power and the feasibility of repeated measurements.