Pyrosequencing method for genotyping cytochrome P450 CYP2C8 and CYP2C9 enzymes.

data show that Greiner lithium-heparin tubes produce a frequency of duplicate errors similar to the frequency of errors obtained with the BD tubes. From the data obtained, use of the modified Modular P IFCC method substantially reduced but did not totally eliminate duplicate errors. For many years, we have observed on an intermittent basis duplicate errors when using lithium-heparin gel tubes (5). These have been most prominent with analytes such as LD, phosphate, sodium, chloride, and potassium on the Hitachi series analyzers. These errors are attributable to cell aggregates, or microclots, which can be throughout the sample but are typically seen floating at the top of the meniscus and almost exclusively in lithium-heparin plasma. In the most recent study we conducted with Greiner (prod. no. 455083) and BD (prod. no. 367377) lithium-heparin tubes with a new gel formulation, we found that 8% and 4%, respectively, of tubes had micro-clots present on top of the meniscus that were visible to the naked eye (Fig. 1). We wish to highlight that both lithium-heparin tubes have gel formulations that are not microclot free. The microclot problem is dramatically reduced in serum samples. In the Hitachi analyzers, the analyte sample volume ranges from 2 to 32 ␮L. To aspirate the sample volume, the probes descend only 2–3 mm into the sample below the meniscus. The presence of cell aggregates (fibrin as well as erythrocytes, leukocytes, or platelets) or micro-clots can cause sampling problems. This can lead to short sampling if the probe picks up the designated sample volume with a microclot as part of the total sample volume. Alternatively, if the microclot disintegrates, the cells may rupture as a result of reagent (pH) changes, releasing the cellular contents (e.g., LD, phosphorus, and aspartate aminotransferase). In contrast, if the sample probe picks up a microclot (plus or minus cell aggregates), and the microclot hangs on the outside of the sample probe, then an additional sample volume may be aspirated and dispensed. Additionally, intact microclots in the reaction cuvette may produce optical interferences as the microclots floats in front of the photometric light path. The potential of microclots to alter the accuracy of assays such as LD using plasma samples is ever present. Vigilant scans by operators of primary lithium-heparin plasma samples from the top is essential. The Modular P IFCC modified method with a predilu-tion step minimizes duplicate errors by diluting the sample in saline …