Reversed whole PTH/intact PTH ratio as an indicator of marked parathyroid enlargement: five case studies and a literature review

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.