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Parathyroid hormone (PTH) levels measured with the intact PTH assays are generally higher than those measured with the whole PTH assay; however, rare exceptions to this rule have been reported in patients with severe hyperparathyroidism associated with N-PTH overproduction. We report a haemodialysis patient with severe secondary hyperparathyroidism, in whom abnormally higher whole PTH levels than intact PTH levels were normalized during cinacalcet therapy. Moreover, we observed a marked reduction in parathyroid gland vascularity during this treatment. Our findings suggested that increased sensitivity of the parathyroid calcium sensing receptor by calcimimetics may modulate the secretion or truncation of N-PTH or other PTH molecules that can be detected by the whole PTH assay but not by the intact PTH assays. [ABSTRACT FROM PUBLISHER]

Parathyroid hormone (PTH) levels detected by intact PTH assays are generally higher than those detected by the whole PTH assay because the latter does not detect non-(1–84) PTH fragments, mainly PTH (7–84). Rare exceptions to this rule have been reported in patients with severe primary or secondary hyperparathyroidism and parathyroid carcinoma. Overproduction of an N-form of PTH other than PTH (1–84) has been observed in the sera of these patients. We report five additional cases with the reversed whole PTH/intact PTH ratio associated with severe hyperparathyroidism in haemodialysis patients. Three patients demonstrated enlargement of a single hypervascular gland, whereas the other two had undergone surgical parathyroidectomy and later showed recurrent hyperparathyroidism due to progressive autograft hyperplasia. In the case of a single enlarged gland, the pathological pattern and heterogeneous expression of parathyroid adenomatosis 1/cyclin D1 suggested it to be a single nodule of uraemic hyperparathyroidism rather than sporadic primary adenoma. These cases suggested that the reversed whole PTH/intact PTH ratio could be an indicator of marked parathyroid enlargement. Further studies are required to elucidate the clinical significance of the reversed whole PTH/intact PTH ratio in haemodialysis patients. [ABSTRACT FROM PUBLISHER]