Preanalytical stability of maternal serum markers hCGß and PAPP-A.

Down syndrome maternal serum marker screening is based on a risk calculation including the free ß - human chorionic gonadotropin (hCGß) and pregnancy-associated placenta protein type A (PAPP-A). The aim of this study was to define the pre-analytical conditions of stability of these markers both in whole blood at 15-25 ÌŠC and, after centrifugation, in serum at 4-8 ÌŠC. 158 patients were included in the study. Two automated workstations were used for assays, Cobas 8000e602, Roche Diagnostics (58 patients tested) and DELFIAXpress, PerkinElmer (100 patients tested). The stability of markers was studied in whole blood (15-25 ÌŠC) 2, 4, 6 and 8 hours after sampling and in serum stored after centrifugation at 4-8 ÌŠC at 24, 72 and 120 hours. Variations were defined by (CT - C2)/C2, C2 being the marker concentration at 2 hours and CT the concentration at time T. In whole blood kept for 8 hours at 15-25 ÌŠC, hCGß increased by a mean 2.4%, whereas the mean increase of PAPP-A was < 1%. In the serum kept for 5 days at 4-8̊C, the mean increase of hCGß was 4.2%, with no change in PAPP-A. The impact of these variations on risk calculation is low. In conclusion, maternal serum can be store 8 hours at 15-25̊C in whole blood and 5 days at 4-8̊C after centrifugation and serum separation for Down syndrome maternal serum screening.

Comparison of hepatitis C virus NS5b and 5' noncoding gene sequencing methods in a multicenter study.

A national evaluation study was performed in 11 specialized laboratories with the objective of assessing their capacities to genotype hepatitis C virus (HCV) and define the applicability of a given genotyping method. The panel consisted of 14 samples positive for HCV RNA of different genotypes (including 3 samples with two different artificially mixed genotypes) and 1 HCV-negative sample. Seventeen sets of data were gathered from the 11 participating laboratories. The sensitivities ranged from 64.3 to 100% and from 42.7 to 85.7% for the methods that used sequencing of the NS5b region and the 5' noncoding (5' NC) region, respectively. When the data for the artificially mixed samples were excluded, NS5b genotyping gave correct results for 80% of the samples, 1.7% of the samples were misclassified, and 18.3% of the samples had false-negative results. By 5' NC-region genotyping methods, 58.3% of the results were correct, 29.7% were incomplete, 8.3% were misclassifications, 1.2% were false positive, and 2.4% were false negative. Only two procedures based on NS5b sequencing correctly identified one of the three samples with mixtures of genotypes; the other methods identified the genotype corresponding to the strain with the highest viral load in the sample. Our results suggest that HCV 5' NC-region genotyping methods give sufficient information for clinical purposes, in which the determination of the subtype is not essential, and that NS5b genotyping methods are more reliable for subtype determination, which is required in epidemiological studies.