A nomogram to predict C282Y hemochromatosis.

Genetic testing of hemochromatosis has not been widely used as a diagnostic test because of unawareness of its existence and concerns about genetic discrimination. We developed a nomogram for the prediction of C282Y homozygotes for hemochromatosis from transferrin saturation and ferritin using Bayes theorem. The results of transferrin saturation and C282Y genotyping were available for 8,572 participants (5,042 men, and 3,530 women). The study group included patients in population-screening projects, referred cases, and family members. Likelihood ratios were calculated for transferrin saturation in predicting C282Y homozygotes. Pretest probabilities were estimated on the basis of serum ferritin concentration, and a predictive nomogram for men and women was created with the use of Bayes' theorem. In the highest-risk region of the nomogram in men, the probability of C282Y hemochromatosis was 89.7% (95% confidence interval = 85.1-94.3); in the lowest-risk zone it was 1.1% (0.4-1.9). The corresponding regions in women were 88.9% in the high zone (95% confidence interval = 77.0-100.0) and 6.5% in the lowest (95% confidence interval = 4.9-8.1). This approach allows the clinician to predict the probability of a patient's being a C282Y homozygote over a wide range of ferritin and transferrin saturation values instead of above a particular threshold.