This paper reports on the diagnostic usefulness of two commercial PTH assay kits and four #x201C;in-house#x201D; assays using commercially available reagents, studying the same samples from normal controls and different patient groups. The ability of such assays to discriminate proven primary hyperparathyroid (1#xB0; HPT) patients from normals varied significantly but without any apparent correlation with assay components. For all assays, performance declined markedly in 1#xB0; HPT patient groups with lower serum calcium levels. Patients with PTH secondary to chronic renal disease were well discriminated from normal by all assays. Although immunoassays are useful in many cases of 1#xB0; HPT, it is difficult to develop C-terminal or mid-region PTH assays that are uniformly diagnostically useful in the clinical situation where they are of greatest potential use i.e. in cases of mildly hypercalcaemic 1#xB0; HPT.
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