Rapid differential diagnosis of Graves' disease and painless thyroiditis using total T3/T4 ratio, TSH, and total alkaline phosphatase activity.

When thyrotoxic patients are first seen in an outpatient clinic, it is important to make a differential diagnosis of Graves' disease (GD) and painless thyroiditis (PT). Using the three parameters of total T3/T4 ratio, TSH and T-ALP activity, all of which can be obtained within one hour in our hospital, 173 untreated patients with thyrotoxicosis were evaluated for the ratio of each parameter. For GD vs. PT, total T3/T4 (ng/microg) ratio (>20), TSH (<0.005 microU/ml) and elevated T-ALP had a likelihood ratio of 2.14, 2.12 and 4.07, respectively. When a patient had all three positive parameters, the likelihood ratio increased to 5.81, which showed effective synergy. These data suggest that, in addition to total T3/T4 ratio and TSH value, T-ALP activity is a useful parameter for the rapid differentiation of GD. The lower T-ALP activity seen in PT is probably due to the fact that patients develop less severe thyrotoxicosis or visit hospital earlier than patients with GD. Therefore, the diagnostic accuracy for Graves' disease might be increased by using the three parameters in combination.