An index based on the age and the free thyroxine rate predicts likelihood of Graves' disease in thyrotoxic patients.

Purpose. - Graves' disease patients are generally younger and have more sev ere symptoms than other thyrotoxic patients. We established an index based on the normalized free thyroxine rate and age, capable of predicting Graves ' disease in thyrotoxic patients. Methods. - The predictive index was established from a discriminant analysi s from a retrospective population of 114 thyrotoxic patients and ifs predic tivity was confirmed by cross-validation on the same population. Results. - The index I-GD = 41.38 - age + 37.05 x In (normalized free T4) c lassifies accurately 80.7% of the patients (CI 95%: 72.2-875). Sensitivity is 78.5% (CI 95%: 66.5-87.7). Specificity is 83.7% (CI 95%: 70.3-92.7). Pre dictive positive value is 86.4% (CI 95%. 75.0-94.0). Negative predictive va lue is 74.5% (CI 95%. 61.0-85.3). Likelihood ratio of Graves' disease in ca se of prediction by the index is 4.81 (CI 95%: 2.66-9.32). Likelihood ratio of Graves' disease in case of non-prediction by the index is 0.26 (IC 95%: 0.16-0.40). Conclusion. - A simple index based on the normalized free thyroxine rate an d age provides an early diagnosis orientation toward Graves' disease in thy rotoxic patients who are waiting for complementary investigations. (C) 2001 Editions scientifiques et medicales Elsevier SAS.