We developed a novel immunoradiometric assay (IRMA; whole parathyroid hormone [PTH] IRMA) for PTH, which specifically measures biologically active whole PTH(1-84). The assay is based on a solid phase coated with anti-PTH(39-84) antibody, a tracer of 125 I-labeled antibody with a unique specificity to the first N-terminal amino acid of PTH(1-84), and calibrators of diluted synthetic PTH(1-84). In contrast to the Nichols intact PTH IRMA, this new assay does not detect PTH(7-84) fragments and only detects one immunoreactive peak in chromatographically fractionated patient samples. The assay was shown to have an analytical sensitivity of 1.0 pg/ml with a linear measurement range up to 2300 pg/ml. With this assay, we further identified that the previously described non-(1-84)PTH fragments are aminoterminally truncated with similar hydrophobicity as PTH(7-84), and these PTH fragments are present not only in patients with secondary hyperparathyroidism (2°-HPT) of uremia, but also in patients with primary hyperparathyroidism (1°-HPT) and normal persons. The plasma normal range of the whole PTH(1-84) was 7-36 pg/ml (mean ؎ SD: 22.7 ؎ 7.2 pg/ml, n ‫؍‬ 135), whereas over 93.9% (155/165) of patients with 1°-HPT had whole PTH(1-84) values above the normal cut-off. The percentage of biologically active whole PTH(1-84) (pB%) in the pool of total immunoreactive "intact" PTH is higher in the normal population (median: 67.3%; SD: 15.8%; n ‫؍‬ 56) than in uremic patients (median:53.8%; SD: 15.5%; n ‫؍‬ 318; p < 0.001), although the whole PTH(1-84) values from uremic patients displayed a more significant heterogeneous distribution when compared with that of 1°-HPT patients and normals. Moreover, the pB% displayed a nearly Gaussian distribution pattern from 20% to over 90% in patients with either 1°-HPT or uremia. The specificity of this newly developed whole PTH(1-84) IRMA is the assurance, for the first time, of being able to measure only the biologically active whole PTH(1-84) without cross-reaction to the high concentrations of the aminoterminally truncated PTH fragments found in both normal subjects and patients. Because of the significant variations of pB% in patients, it is necessary to use the whole PTH assay to determine biologically active PTH levels clinically and, thus, to avoid overesti-

Standardization of methods for the quantification of 25(OH)D on a human-based sample panel by means of LCMS/MS would help to reduce the inter-method variability with respect to accuracy existing in 25(OH)D measurement considerably. However, there will still remain differences in the accuracy of methods utilizing sample purification before final quantification or immunological reaction when compared with those methods without separate sample purification.

ABSTRACT

Studies in the past showed elevated immunoreactive parathyroid hormone (PTH) serum values in early renal failure, but the assays used in these studies could not discriminate between bioinactive fragments of the PTH peptide and biologically active hormone. The availability of a sensitive PTH assay, which quantitates intact hormone, now allows the analysis of biologically active PTH in renal failure. To characterise more precisely the point of onset of hyperparathyroidism in the course of chronic renal failure and its relation to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], we measured plasma intact PTH and vitamin D metabolite serum values in 63 non-nephrotic uraemic patients (male n = 35, female n = 28, age 31-78 years) with incipient (GFR 60-90 ml/min per 1.73 m3, n = 19) mild (GFR 40-60, n = 22) and moderate (GFR 20-40, n = 22) renal failure, and in 22 age-matched healthy control subjects. Intact PTH concentrations were negatively correlated with GFR (r = -0.57, P less than 0.001). Median plasma intact PTH values (normal range 1.2-6 pmol/l) were 5.6 (range 2.2-13.0) in incipient, 8.1 (2.9-24.0) in mild, and 13.0 (5.4-59.0) in moderate renal failure. Intact PTH values in incipient renal failure were significantly greater than in 22 age-matched control subjects (P less than 0.01). The decline of GFR was paralleled by a progressive decrease in 1,25(OH)2D3 serum values (r = 0.44, P = 0.001). Median values of the hormone (normal range 35-90 pg/ml) were 32 (range 20-66) in incipient (P less than 0.01 vs. age-matched control subjects), 34 (22-74) in mild, and 26 (17-39) in moderate renal failure. In all three groups, mean serum phosphate and total calcium concentrations (corrected for serum protein) were within the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied clinical performance of serum TRACP 5b and other bone turnover markers, including S-CTX, U-DPD, S-PINP, S-BALP, and S-OC, for monitoring alendronate treatment. TRACP 5b had higher clinical sensitivity, area under the ROC curve, and signal-to-noise ratio than the other markers.Introduction: The purpose of this study was to compare the clinical performance of serum TRACP 5b (S-TRACP5b) with that of other markers of bone turnover in the monitoring of alendronate treatment. Materials and Methods: This double-blinded study included 148 healthy postmenopausal women that were randomly assigned into two groups: one receiving 5 mg alendronate daily (n ‫ס‬ 75) and the other receiving placebo (n ‫ס‬ 73) for 12 months. All individuals in both groups received calcium and vitamin D daily. The bone resorption markers S-TRACP5b, serum C-terminal cross-linked telopeptides of type I collagen (S-CTX), and total urinary deoxypyridinoline (U-DPD), and the serum markers of bone formation procollagen I N-terminal propeptide (S-PINP), bone-specific alkaline phosphatase (S-BALP), and total osteocalcin (S-OC) were assessed at baseline and at 3, 6, and 12 months after initiation of treatment. Lumbar spine BMD (LBMD) was measured at baseline and 12 months. Results: Compared with the placebo group, LBMD increased, and all bone markers decreased significantly more in the alendronate group (p < 0.001 for each parameter). The decrease of S-TRACP5b after first 3 months of alendronate treatment correlated significantly with the changes of all other markers except S-OC, the best correlation being with S-CTX (r ‫ס‬ 0.60, p < 0.0001). The changes of LBMD at 12 months only correlated significantly with the changes of S-TRACP5b (r ‫ס‬ −0.32, p ‫ס‬ 0.005) and S-CTX (r ‫ס‬ −0.24, p ‫ס‬ 0.037) at 3 months. Based on clinical sensitivity, receiver operating characteristic (ROC) curves, and signalto-noise ratio, S-TRACP5b, S-CTX, and S-PINP were the best markers for monitoring alendronate treatment. Clinical sensitivity, area under the ROC curve, and signal-to-noise ratio were higher for S-TRACP5b than for the other markers. Conclusion: These results show that S-TRACP5b, S-CTX, and S-PINP are useful markers for monitoring alendronate treatment.