Serum ferritin measurement and the degree of agreement using four techniques.

Four commercial assay kits to measure serum ferritin were compared to establish the degree of agreement and interchangeability between the different techniques based on the intraclass correlation coefficient (ri). Radioimmunoassay, microparticle enzyme immunoassay, enzyme-linked immunosorbent assay, and chemiluminescent immunoassay systems were used. The Pearson product-moment correlation factor (r) between any two methods was at least 0.98, and the intercept of the regression equations ranged from -0.613 to 3.797, indicating that the methods were comparable. Furthermore, the intraclass correlation coefficient (ri) was at least 0.98, suggesting that the methods were interchangeable.