Relative contribution of various expressions of cAMP excretion to other indices of parathyroid function, as tested by...

We evaluated the relative contribution to the diagnosis of hyperparathyroid disease from current laboratory indices of parathyroid function--plasma calcium (I), phosphate (II), carboxy-terminal (III) and predominantly amino-terminal (IV) radioimmunoassays of parathyrin, the urinary excretion ratios of cyclic adenosine monophosphate (cAMP) to creatinine (V) or to glomerular filtrate (VI), and the ratio of the nephrogenous fraction of cAMP to glomerular filtrate (VII)--in 224 subjects: 40 with surgically proven hyperparathyroid disease, the others normoparathyroid. The decreasing order of sensitivity was I greater than VI greater than VII greater than V greater than III greater than IV greater than II; all these indices differed significantly between normoparathyroid and hyperparathyroid patients. The decreasing order of specificity was VII, III greater than I greater than IV greater than V, II greater than VI. Discriminant multivariate linear regression analysis was performed in a subset of 58 subjects (17 hyper- and 41 normoparathyroid) from the population studied here, chosen because all of the laboratory indices were determined for each subject. The classification accuracy was 98.3% for combining I, VII, and III (r = 0.908), or I and V (r = 0.893), or I and VII (r = 0.889). The other variables did not add to the precision of classification.