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PubMed2003

Evaluation of a fully-automated particle-enhanced turbidimetric immunoassay for the measurement of plasma lipoprotein(a). population-based reference values in an area with low incidence of cardiovascular disease.

OBJECTIVES: Lipoprotein(a) has been proposed as an independent risk factor for cardiovascular disease. This lipoprotein possesses a marked size polymorphism that makes difficult to measure accurately its concentration in plasma. The International Federation of Clinical Chemistry recently recommended to carefully evaluate new commercial methods for lipoprotein(a) measurement to discard the possible influence of lipoprotein(a) isoforms on immunoreactivity. They also recommended to perform population-based studies for different ethnic and geographic groups. Therefore, in the evaluation of a fully automated, particle-enhanced turbidimetric immunoassay for the measurement of lipoprotein(a) we have determined its reference interval in the Spanish population, an area with the lowest incidence of cardiovascular disease in Europe. DESIGN AND METHOD: We evaluated a commercial kit of reagents calibrated against the Proposed Reference Material and determined the effect of lipoprotein(a) size polymorphism on the measurements. A population-based study was carried out in two different villages on the Mediterranean coast of Spain. RESULTS: Imprecision at different lipoprotein(a) concentrations ranged between 3.0 and 15.4%. Recovery was 98.5 +/- 2.1. Detection limit was 4.8 nmol/L. There were no significant interferences from lipemia, jaundice, hemolysis, paraproteinemia, apolipoprotein B or plasminogen. We did not observe any effect of the lipoprotein(a) size polymorphism on the measurements. Mean (and SD) values for plasma lipoprotein(a) (n = 369) were 53.6 (65.3) nmol/L, the median was = 25.3 nmol/L and range varied between <4.8 and 356.0 nmol/L. CONCLUSION: The present article presents an accurate and practical assay for measuring plasma lipoprotein(a) concentrations and describes its reference values in a population of Spanish Caucasians. Our results are similar to those obtained in other Caucasian populations (between 10 and 25% higher than in participants of the CARDIA study).

Adolescent↗
PubMed2001

Uniformity test of bias when the reference value contains experimental error.

The uniformity test of biases for analytical methods must address uncertainties in the reference method. If the uncertainty associated with the estimates of true values is significant but ignored in the test of bias equality, the type I error can exceed the prespecified error rate. In general, when biases at each concentration level are confounded with a random component (confounding bias), the usual test of bias equality tests the uniformity of the combined bias, rather than the uniformity of fixed bias-the bias without the random component. Based on a confounding model that takes both the fixed and the confounding biases into account, the actual type I error rate of the uniformity test can be calculated. To eliminate the impact of confounding bias on the uniformity test of fixed biases, a new F'-test is proposed. The new F'-test is simply adding a correction factor to the conventional F-test. The correction factor is directly related to the uncertainty associated with the estimates of true values. A simulation study is conducted to show that the proposed test can bring the type I error rate down to the prespecified level. Data from two aldehyde methods are used to demonstrate how the proposed F'-test works. Recommendations on optimal sample allocation are also provided.

Aldehydes↗