Inter and Intra Laboratory Variation of Digoxin Radioimmunoassay in Sweden

Publisher Website
Google Scholar
Abstract
Samples from 2 pools were sent 10 times to 27 laboratories for digoxin assay. One pool contained digoxin 2.60 nmol/l in normal plasma (SP); the other was pooled plasma from patients treated with digoxin (PP). Ten radioimmunoassay (RIA) methods were used. The SP assay mean was 2.59 nmol/l, not significantly different from 2.60 nmol/l. The mean PP determination was 2.46 nmol/l. Within each of the 10 assay rounds, the concentrations showed an almost 2-fold variation and SD averaged 0.33 and 0.31 nmol/l for SP and PP, respectively. Significant differences (P < 0.001) were found between mean concentrations obtained for pools at various laboratories (SP range 2.15-2.85 nmol/l; PP range 2.12-2.72 nmol/l). The laboratory means obtained for SP and PP correlated significantly (P < 0.001). Significant (P < 0.01) variations between laboratories were found concerning mean difference between SP and PP concentrations. The interassay SD of the assays differed significantly between laboratories (range 0.05-0.61 nmol/l). Between and within laboratory groups using the same RIA method and between various laboratory types, differences were found concerning assay accuracy and precision. Apparently a better digoxin control assay is needed.