RESUMO
BACKGROUND: Small dense low density lipoprotein (sdLDL) plays a critical role in the progression of coronary vascular disease. However, regardless of the accuracy of the analytical technique, routine measurement of LDL does not precisely ascertain LDL particle size. Therefore, we evaluated the performance of a direct quantitative assay of sdLDL that combines a precipitation method with filtration (Denka Seiken, Japan). METHODS: We evaluated the precision, linearity, carry-over, and sample stability of a sdLDL reagent. A reference interval was established, and method comparison was performed with the Lipoprint LDL system using polyacrylamide gel tube electrophoresis (Quantimetrix, USA). RESULTS: The within-run precision was 0.9% to 1.4%, with a total precision of 3.2% to 3.5%. The analytical measurement ranged from 4.1 to 101.3 mg/dL. The calculated carry-over was negligible (0.1%). Based on a comparison conducted using the Lipoprint LDL system, the median sdLDL concentration of 57 individuals with phenotype non-A was found to be significantly higher than that of 51 subjects with phenotype A (43 vs. 22 mg/dL, P<0.0001). The levels in samples retested after storage showed more than 95% recovery when stored in a refrigerator (5degrees C) for 2 weeks and at -20degrees C or lower for 4 weeks. The reference interval of sdLDL was between 7.6 and 52.0 mg/dL. CONCLUSIONS: This method of sdLDL measurement showed good performance and can be easily applied to automated analysers in clinical laboratories.