AbstractFerritin is an indispensable parameter in the diagnosis of latent iron deficiency anemia or siderosis. In this study, we evaluated the utility of a reagent for ferritin measurement in a latex agglutination (LA) test, using general chemistry analyzers. The intraassay coefficient of variation (CV) was 0.8–3.4% and the interassay CV was 0.0–0.7%. Linearity was observed up to 1,100 ng/mL. The effective sensitivity value was 4.0 ng/mL. In addition, good results were obtained with the prozone test, the effects of interferences, correlation with the enzyme immunoassay (EIA) method, and functional assay sensitivity. A significant positive correlation with C‐reactive protein (r=0.586, P<0.001) was found. When compared with liver‐related biochemical parameters (asparate aminotransferase (AST) and alanine aminotransferase (ALT)) in patients with impaired liver function, ferritin varied in parallel with the liver‐related parameters. This assay system was able to measure ferritin accurately over a wide range, and thus could be used to diagnose cancer, siderosis, and iron deficiency anemia. The LA assay system can be employed for measurement with general chemistry analyzers, with rapid and convenient execution. In addition, the LA test allows the simultaneous measurement of other markers of iron deficiency anemia, so clinicians can rapidly obtain examination results. J. Clin. Lab. Anal. 17:223–228, 2003. © 2003 Wiley‐Liss, Inc.