Interference in an automated radial partition fluorescent immunoassay of thyrotropin associated with liver-function abnormalities.

In a previous evaluation of a "sensitive" radial partition fluorescent immunoassay on the Stratus system, thyrotropin (TSH) values exhibited a positive bias in icteric samples when compared with results of a nonsensitive radioimmunoassay. In the present study, we evaluated 366 patients samples to assess whether any biochemical markers of liver function could identify samples for which TSH values would be falsely increased. gamma-Glutamyltransferase and total bilirubin concentrations were unrelated to discrepant TSH values. In contrast, alkaline phosphatase (ALP) was significantly positively correlated with differences in Stratus and RIA TSH concentrations (P less than 0.001). However, this correlation explained only 34% of the observed residual variability around the estimated regression line. On average, the higher ALP values were associated with larger discrepancies between Stratus and RIA TSH values, although several samples with increased ALP did not have falsely increased Stratus TSH values. TSH measurements performed with a Stratus should be interpreted with caution in patients with abnormal biochemical markers of liver function.