Volumen 52 #4 | Año 2015 Volver Indice
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  Test with Calcitriol in the Differential Diagnosis of Hyperparathyroidism  
  Authors: Gamez JM; Martínez MP; Kogovsek N; Salerni HH  
  Primary hyperparathyroidism (PHP) is a disorder characterized traditionally by hypercalcemia and elevated levels of parathyroid hormone (PTH). However, this complete biological pattern is sometimes lacking. Some PHP patients display either normal or intermittently elevated serum calcium level as well as hypercalcemia with normal PTH levels. PTH synthesis is negatively controlled by calcitriol through the vitamin D receptor (VDR). We assessed the diagnostic value of a PTH inhibition test with calcitriol in the diagnosis of PHP, in 103 patients who have minimal, intermittent, or no elevation of the levels of total or ionized calcium, and/or intact PTH. Patients with 25OHD < 20 ng/ml or less than a year follow up were excluded. We measured serum total calcium (CaT), ionized calcium (CaI), PTH and urinary calcium in 47 patients before and after the oral administration of calcitriol 0.75 ug once daily for 10 days. The biochemical response was classified as A) increase in serum calcium with high or normal PTH levels (PHP) or B) PTH suppression without hypercalcemia (secondary hyperparathyroidism). PHP was confirmed by images or surgery. The two groups were similar in age and 25 OHD levels. The mean follow up was 70 ± 34 months. Basal serum CaT and CaI were higher in group A. After the loading, this difference was even bigger, what gives additional specificity to the measure. Urine calcium was equally augmented by calcitriol in both groups, with coincident elevation of serum calcium in group A but not in B, in which serum calcium remained stable. Basal PTH levels were similar in both groups, so they cannot reliable distinguish between both types of hyperparathyroidism. After the calcitriol load, PTH dropped 44 % ± 18 in group B versus 15 % ± 27 in group A, suggesting some degree of resistance to the hormone action in PHP. ROC curves shows that a reduction of less than 30 % in PTH levels can diagnose PHP with 85% sensibility and 88% specificity. Only two patients in group B behaved as PHP at 17 and 37 months follow up, what gives the test 90 % sensibility and 100 % specificity for the diagnosis of PHP. So, this well-tolerated and easily performed test could be used for the diagnosis of PHP in patients suspected for the disease despite the normality of some basal biological markers.

Rev Argent Endocrinol Metab 52:185-193, 2015
No financial conflicts of interest exist.
  Key words: test with calcitriol, primary hyperparathyroidism  
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