[Current function tests in hypoparathyroidism in children].

In clinical practice, we can now directly measure the level of circulating parathormone and we can also assess its impact on its renal effector by the assay of cyclic adenosine monophosphate. The radio-immunoassay of parathormone uses antisera with amino or carboxy terminal specificity. The preferential antibody has amino-terminal specificity in as much as the biological activity resides in this part of the hormone, so that the levels measured with this antibody reflect the levels of biologically active parathormone. However, the levels detected with antisera with carboxy-terminal specificity are much more discriminating in cases of hormonal hypersecretion in pseudohypoparathyroidism, because of the prolonged survival time of the fragments detected. The study of the sensitivity of the renal receptor to parathormone is based on the Ellsworth-Howard test. The plasma cyclic AMP gradient is measured following injection of exogenous parathormone. The results demonstrate a definite absence of response in the pseudohypoparathyroid children studied compared to normal and hypoparathyroid children. In children with hypoparathyroidism, the response is rapid with a maximal level of cyclic AMP obtained at 10 minutes. The gradient can be as much as 20 times the baseline level. The study of the sensitivity of the bone receptor to parathormone is based on classical tests whose results are difficult to evaluate, like changes in the serum calcium and the total urinary hydroxy-proline obtained after an injection of exogenous parathormone.