Comparison of gene expression profiles in laser-microdissected, nonembedded, and OCT-embedded tumor samples by oligonucleotide microarray analysis.

samples and hemolysis can be responsible for LD measurements with poor precision in addition to higher LD activity values (7, 8). To investigate these effects, we performed LD measurements with serum-gel (Sarstedt Monovette prod. no. 02.1388), lithium-heparin-gel (same as given above), and lithium-heparin tubes (Sarstedt Monovette prod. no. 01.1604.400). Blood samples were collected from the same person in five different tubes and centrifuged differently to obtain various degrees of plate-let contamination. Serum-gel, lithium-heparin-gel, and lithium-heparin samples were centrifuged for 10 min at 3000g or for 5 min at 500g. Platelet counts were done for all samples (Max M; Beckman-Coulter). IFCC-recommended serum samples had very low platelet contamination , even after reduced centrifugation (see Table 1). Standard-centrifugation lithium-heparin samples contained platelet-poor plasma, whereas reduced centrifuga-tion produced platelet-rich plasma (Table 1). LD activity was measured (n ϭ 77) for each of the five types of sample. The higher platelet contamination of the samples in case of reduced centrifugation caused only a small increase of the within-run CV: 2. for samples with low platelet contamination (Table 1). The mean LD activity for standard-centrifugation lithium-heparin-gel samples was higher than the activity for the corresponding serum-gel samples (mean difference, 28.8 U/L) and the corresponding reduced-centrifugation lithium -heparin-gel samples (Table 1). This may be the result of platelet destruction with subsequent release of intracel-lular LD. Lithium-heparin samples showed the same LD activity as lithium-heparin-gel samples despite higher platelet contamination. These results demonstrate that very high platelet contamination may have a small influence on the performance of the LD assay, but again, it would not account for the reported high frequency of duplicate errors. Bakker et al. (1) found different frequencies of duplicate errors for heparin-plasma samples with (19%) and without separator (35%), and they could show that after heparin-plasma samples were transferred to secondary tubes (efficient mixing), the frequencies of duplicate errors dropped to 1.1%. We speculate that in the case of the Becton Dickinson heparin-plasma tubes used, both partial instability of the gel as well as inhomogeneities attributable to platelets and platelet aggregation might have caused the described problems. In combination with the specific sampling tubes, different variables, including blood sample collection, time between blood draw and centrifugation, reduced centrifugation, temperature, or specific analyzer features (e.g., rinsing program, sample and reagent volumes, or timing) could also contribute to the high frequency of duplicate errors. We conclude that the IFFC method from Roche for LD measurement …