Measurement of the acid-labile subunit of the insulin-like growth factor binding protein complex in human serum: a comparison of four immunoassays

The acid-labile subunit (ALS) of the high molecular weight insulin-like gro wth factor binding protein complex is a liver-derived glycoprotein which is regulated by growth hormone and serves as a serum marker of growth hormone action. We have compared the measurement of ALS by four immunoassay method s (two RIAs, two ELISAs) utilizing various polyclonal and monoclonal antibo dies raised against natural or recombinant human ALS, or synthetic ALS pept ides. Despite the variety of methodologies and reagents, results obtained b y the four methods were highly correlated for 125 sera from various patient groups, and when compared for individual groups of sera from healthy child ren and adults, growth hormone-deficient children and adults, and subjects with acromegaly. Some weaker correlations among methods were seen when meas uring ALS levels in groups of sera from pregnant subjects and subjects with chronic renal failure. An assay using antibodies raised against recombinan t ALS yielded lower apparent values than the other methods in patient sera, the discrepancy probably being attributable to a difference in standardiza tion. We conclude that a variety of assay formats and reagents can yield se rum ALS values of potential clinical utility.