[Determination of methotrexate concentration in serum: comparison between capillary and venous blood]

The methotrexate serum concentrations of 15 patients were measured in capillary and veneous blood samples. All of the patients had received methotrexate infusions because of their underlying oncologic disorder. The drug levels of 42 pairs of capillary and veneous drawn serum samples were analysed with a homogeneous enzyme immunoassay technique on a semi-automatic instrument system. In 15 pairs of samples the drug levels were below the range of the assay, in 3 they were just above. Here the capillary samples were measurable, whereas the veneous ones were not. 24 pairs of samples which had drug levels within the range of the assay showed a good correlation of capillary and veneous serum levels. The correlation factor of 0.934 shows, that the methotrexate concentrations can also be measured in capillary blood samples.