A simple turbidimetric assay designed for the routine screening as well as therapeutic monitoring of native LDL particles.

We describe the development and performance of a homogeneous assay for the direct turbidimetric determination of LDL particles in human serum. The assay is based upon the specific agglutination of LDL particles by the polyanion PAMPS. The co-agglutination of VLDL is avoided by the addition of a zwitterionic detergent. Yielding results within 10 min, the assay requires only a small sample volume taken directly from primary serum tubes, i.e., no pretreatment of the sample is necessary. It can be easily applied to routine clinical chemistry analyzers. The results are highly correlated with LDL cholesterol determinations by ultracentrifugation (r>0.95) and dextran sulfate precipitation (r>0.95), but an increased recovery of small, high density LDL particles is observed, which more adequately reflects the atherogenic risk of LDL. The assay provides excellent intra- and inter-assay CVs in the range of 0.6--1.6 and 1.7--2.4%, respectively, on Roche Diagnostics/Hitachi analyzers. The method is well suited to the high-throughput screening of LDL cholesterol levels.

Development and evaluation of assays for the determination of total and pancreatic amylase at 37 degrees C according to the principle recommended by the IFCC.

OBJECTIVES: The aim of our study was a) to optimize assays for measurement of total (T-) and pancreatic (P-)amylase at 37 degrees C based on the principle recommended by the IFCC at 30 degrees C, b) to evaluate the analytical performance of these assays in a multicentric study and c) to establish reference intervals for serum and urine for either method. METHODS: Optimized conditions for 37 degrees C were elaborated with regard to substrate concentration, pH, inorganic additives and glucosidase activity. The cleavage pattern of the EPS substrate was studied by HPLC. Liquid ready-to-use reagents for T- and P-amylase were provided to six European laboratories. RESULTS: The assays showed good performance characteristics (median intraassay CVs 1.0% for T- and 1.3% for P-amylase, median interassay CVs 3.0% for either assay, dynamic range 15-fold URL for T- and 30-fold for P-amylase), high correlation with the previous EPS methods (r > 0.996, slope 0.43, intercept < 5 U/L) in serum, heparin plasma and urine and good analytical specificity of the P-amylase assay (residual S-amylase activity 2.4%). Serum reference ranges were found to be 28 to 100 U/L for T- and 13 to 53 U/L for P-amylase (n = 775); URLs in urine were estimated as 490 U/L or 280 U/g creatinine for males and 450 U/L or 380 U/g creatinine for females with total amylase. CONCLUSION: We believe that these assays based on the 30 degrees C IFCC recommendation represent a further improvement in amylase methodology at 37 degrees C and merit broad application in clinical routine.