Efficacy of whole PTH assay and 1-84/non-(1-84) PTH ratio in patients on hemodialysis or undergoing parathyroidectomy

Abstract

著者らは27名の健常者と138名の慢性透析患者を対象として, whole PTH(W-PTH), intact PTH(I-PTH), PTH ratio(PTH1-84とnon 1-84 PTHの比)を測定または算出し, 骨型ALP(BAP)やインタクトオステオカルシン(BGP-I)などの血中骨代謝マーカーと比較した.また, 2次性副甲状腺機能亢進症により副甲状腺全摘出術(PTx)を受けた10名の患者を対象として, 手術前後の各パラメーターの変化について検討し, W-PTH, PTH ratioの有用性を検討した.その結果, 1)健常者と透析患者の両群でW-PTHとI-PTHの間には非常に強い相関を認めた(p<0.001).また透析患者群では, ALP, BAP, BGP-IとW-PTHまたはI-PTHの間にそれぞれ有意な相関を認めたが, PTH ratioと各骨代謝マーカーとの間には相関を認めなかった.2)PTH ratioが1.0以上の患者群は1.0未満の群よりも, W-PTH, I-PTH, BAP, BGP-Iは有意に高値であったが, ratioが1.0以上の患者113名のうち51名はI-PTHが100pg/ml以下であった.PTH ratioはPTx施行後に施行前の値よりも増加する傾向を認めた.以上, これらのことからもW-PTH assayはI-PTH assayとほぼ同様に慢性透析患者における骨代謝の指標となると考えられた.しかしPTH ratioはカットオフ値が1.0の場合, 骨代謝回転の診断には限界があると思われた

For measurement of parathyroid hormone (PTH), the intact PTH (I-PTH) assay is generally used. However, I-PTH assay apparently detects PTH 7-84 fragments, in addition to PTH 1-84. The whole PTH (W-PTH) assay exhibits no cross-reactivity with PTH 7-84. Ratio of PTH 1-84 to non-(1-84) PTH has been proposed as a non-invasive indicator of bone turnover in patients with end-stage renal disease (ESRD). We evaluated the efficacy of W-PTH assay and 1-84/non-(1-84) PTH ratio in hemodialysis patients and patients who had undergone parathyroidectomy. PTH levels were measured using W-PTH and I-PTH assays in 138 hemodialysis patients, 27 healthy controls and 10 patients who were scheduled to undergo parathyroidectomy for secondary hyperparathyroidism. Alkaline phosphatase, bone alkaline phosphatase and intact osteocalcin were also measured for comparison with 1-84/non-(1-84) PTH ratio. W-PTH was strongly correlated with I-PTH in both groups, and with all three bone metabolic markers in hemodialysis patients. In hemodialysis patients, both PTH and bone metabolic markers were significantly lower in the subgroup with a PTH ratio or = 1.0. However, PTH ratio exhibited no significant correlation with bone metabolism markers. PTH ratio was higher after parathyroidectomy than before. W-PTH and I-PTH assays offer identical indicators of bone metabolism in ESRD patients. However, 1-84/non-(1-84) PTH ratio may be of limited diagnostic use regarding bone turnover if a cut-off value of 1.0 is used. PTH 1-84 may be secreted relatively more than non-(1-84) PTH after parathyroidectomy, due to decreases in serum calcium. As the W-PTH assay allows easy calculation of non-(1-84) PTH by subtracting the I-PTH value, this assay contributes to identification of the function of non-(1-84) PTH fragments in various conditions.