Experience with a third-generation parathyroid hormone assay (BIO-PTH) in the diagnosis of primary hyperparathyroidism in a Brazilian population

Abstract

Objective: To evaluate the usefulness of a third-generation PTH assay in the diagnosis of primary hyperparathyroidism (PHPT). Subjects and methods: Forty-one PHPT patients (4 men and 37 women) with 61.2 ± 10.9 (mean ± SD) years, were studied and had PTH levels measured with two different methods using the same immunochemiluminescent assay plataform (Elecsys 2010 System, Roche). We compared a second-generation assay (I-PTH) with a third-generation PTH assay (Bio-PTH). Two populations of 423 and 120 healthy adults with serum 25OHD levels above 25 ng/mL were used to define normal values in the I-PTH and Bio-PTH assays respectively. Results: Normal PTH values based in the healthy adults population were 24.2-78.0 pg/mL for the I-PTH assay and 19.9-58.5 pg/mL for Bio-PTH assay. In PHPT patients, PTH values ranged from 67 to 553 pg/mL (median: 168 pg/mL) using the I-PTH assay and from 55 to 328 pg/mL (median: 111 pg/mL) using the Bio-PTH assay. Results obtained with the Bio-PTH assay were significantly lower (p < 0.0001, Wilcoxon). In general I-PTH and Bio-PTH showed highly significant correlation (r = 0.952, p < 0.0001). Passing-Bablok analysis gave a regression equation of Bio PTH = 13.44 + 0.59 x intact PTH. PHPT patients had 25OHD levels ranging from 4 to 36 ng/mL (mean 16.2 ng/mL); 35 subjects (85.3%) had values bellow 25 ng/mL. Conclusion: Our results demonstrate that both second and third generation PTH methods are strongly correlated in PHPT patients and control subjects. Lower results with Bio-PTH tests are expected in function of the assay specificity determined by the amino-terminal antibody used. Arch Endocrinol Metab. 2016;60(5):420-5

Parathormone Levels in a Middle-Eastern Healthy Population Using 2nd and 3rd Generation PTH Assays

“…Few studies compared the two PTH generations in the same sample: in French healthy subjects [4] PTH concentration did not differ according to the generation of the used kits, except for an overestimation with the 2 nd generation assays for values beyond 200 pg/ml. In another study [5], there was poor concordance between the methods; moreover, this worsened in the higher range of measurements.…”

“…Older PTH assays, called second (2 nd ) generation assays or "intact" PTH, are known to measure not only the 84 amino acid molecules but also to cross-react with a truncated PTH fragment called the 7-84 PTH, whereas the more recently introduced assays, named the third (3 rd ) generation assays, do not measure this truncated fragment, but may cross-react with another fragment called amino-PTH [3]. is difference explains the higher PTH values obtained with 2 nd generation assays compared with the 3 rd generation ones in healthy subjects [4,5] as well as in subjects with chronic renal failure [4,6,7].…”

“…In addition, reference values were mainly established using either 2 nd or 3 rd generation PTH assays. Few studies compared both assays in healthy adults [4,5,19] and included only a small number of subjects [4,19]. It is thus unclear if there is a difference in normative values between both assays.…”

PTH assays in dialysis patients: Practical considerations

“…37 They tested a standard conversion factor (54%) to calcu- While studies have generally shown excellent correlation between second and third-generation assays, 39,40 the preferred comparison should be based on methods that assess agreement. 41 In a small study, Gannagé-Yared et al found that, in hemodialysis patients, the correlation is strong when PTH values are relatively low and gets weaker as PTH levels rises. This is could be in part attributable to the accumulation of C-PTH 7-84 fragments in dialysis patients.…”

“…For instance, Kazama et al showed that patients receiving IV maxacalcitol therapy (active vitamin D analogue) have greater reductions in the third‐generation PTH than the second‐generation PTH levels . While studies have generally shown excellent correlation between second and third‐generation assays, the preferred comparison should be based on methods that assess agreement …”