Glomerular filtration rate and parathyroid hormone secretion in primary hyperparathyroidism

The recent Third International Workshop on the Management of Asymptomatic Primary Hyperparathyroidism (PHPT) set 60 ml/min as the precise level of glomerular filtration rate (GFR) below which surgery is recommended because it is considered a threshold of concern in patients with PHPT.

The aim of the study was to investigate the relationship between different stages of renal insufficiency and PTH levels in PHPT patients.

We conducted a cross-sectional study.

We studied 294 consecutive PHPT patients. Biochemical evaluation included total and ionized serum calcium, phosphate, creatinine, immunoreactive intact PTH, and 25-hydroxyvitamin D3 levels in the fasting state. GFR was assessed with the Modification of Diet in Renal Disease Study formula.

The mean GFR of the whole group of PHPT patients was 92.3 +/- 31.6 ml/min x 1.73 m(2). The patients were divided into four groups according to National Kidney Foundation Disease Outcomes Quality Initiative (K/DOQI) guidelines: group 1 with normal or increased GRF (>90 ml/min x 1.73 m(2); n = 153); group 2 with mild decreased GFR (60-89 ml/min x 1.73 m(2); n = 90); group 3 with moderately decreased GFR (30-59 ml/min x 1.73 m(2); n = 45); and group 4 with severely decreased GFR (<30 ml/min x 1.73 m(2); n = 6). PTH levels were comparable across groups 1-3, whereas group 4 showed significantly higher PTH levels (P < 0.0001).

In our series of PHPT patients, only a severe impairment of GFR was characterized by a further PTH increase. These findings challenge the concept of a PTH elevation below the threshold of 60 ml/min of GFR.