Endocrine Abstracts

Background and aim: Parathyroid hormone (PTH) measurement is critical to evaluate bone status in patients with chronic renal failure as adynamic bone (AB) and bone with a high turnover (HTB) require different therapeutic options. Since the 2nd generation PTH assays recognise a non 1–84 PTH fragment in addition to the intact 1–84 PTH, a new assay defined as 3rd generation has been commercialised. The aim of this study was to evaluate, in dialysed patients, the rate of false classification of the bone status by using a 2nd generation assay hypothesising that a 3rd generation assay is a gold standard.

Patients and methods: 120 newly hemodialysed patients (45F 75M, 59 yr old) were recruited during 2m. PTH was measured by i) our routine Ntact PTH SP IRMA (DiaSorin) and ii) duo PTH (Schering/Scantibodies Lab.) which contains 2 PTH assays for total PTH and 1-84 PTH (the active form of PTH also labelled CAP). A ratio CAP/([total PTH] minus [CAP])(i.e. CAP/CIP)<1.3 is indicative of AB.

Results: Among patients with a suspected HTB ([NtacPTH]>300 pg/ml; 42/120) 66% had a ratio <1.3 suggesting AB (false negative AB). Among patients with a suspected AB ([NtacPTH]<100 pg/ml; 27/120) 30% had a ratio >1.3 suggesting HTB. However, all of these patients had [CAP]<70 pg/ml suggesting that the elevated ratio was due to an increase of CIP rather than an increase in CAP, the active form of PTH (i.e. no false negative HTB). Among patients with intermediate bone status (100<[NtacPTH]<300 pg/ml; 51/120) 43% had a ratio >1.3. Of the latter, 27% had [CAP]<100 pg/ml eliminating a HTB diagnosis.

Conclusion: From the data of these unselected patients, it is clear that different generation assays do not classify similarly the patients. One could limit bone biopsy indication to patients with equivocal data.