Clinical application of intact parathyroid hormone assays

Accuracy of PTH assay and corrected calcium in early prediction of hypoparathyroidism after thyroid surgery

Objective

To evaluate the accuracy of the intraoperative parathyroid hormone (ioPTH) and 6-hour PTH (6hPTH) assay in predicting transient hypoparathyroidism after thyroidectomy.

Study Design

A nonrandomized prospective study was conducted on patients undergoing thyroid surgery.

Subjects and Methods

Of 138 patients undergoing thyroid surgery, intraoperative PTH was measured 10 minutes after gland removal. Serum calcium, magnesium, inorganic phosphorus, albumin, and PTH levels were assayed 6 and 16 hours after surgery and daily until patient discharge.

Results

The development of postoperative hypocalcemia was associated with low ioPTH ( P < 0.0001) and 6hPTH ( P < 0.0001) values, and the decline of PTH from baseline ( P < 0.0001). The cutoff for percentage decline of ioPTH and 6hPTH (55.7% and 379%, respectively) was more accurate than an absolute value. Accuracy, and positive and negative predictive values were 88 percent, 63 percent, and 100 percent for ioPTH and 75 percent, 46 percent, and 100 percent for 6hPTH, respectively.

Conclusion

With the use of ioPTH decline in association with 16-hour corrected calcium, it is possible to distinguish early normocalcemic patients from hypocalcemic ones in most cases.

Lack of Comparability of Intact Parathyroid Hormone Measurements among Commercial Assays for End-Stage Renal Disease Patients: Implication for Treatment Decisions

Background: Variability among assays used to measure intact parathyroid hormone (iPTH) is of particular concern because of the routine use of iPTH assay results to guide management of osteodystrophy and calcium metabolism in patients with end-stage renal disease (ESRD). The aim of this study was to determine the extent to which results from commercially available iPTH assays diverge from results obtained with the Nichols Allegro® Intact PTH immunoradiometric assay (IRMA), which was used as evidence in the development of the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative Clinical Practice Guidelines.

Methods: We divided EDTA plasma from 46 dialysis patients with ESRD and measured iPTH values with the following commercially available iPTH assays: Nichols’ Allegro iPTH IRMA, Nichols Advantage® iPTH immunochemiluminescent assay (ICMA), Scantibodies’ Total Intact PTH™ IRMA, DiaSorin’s N-tact® iPTH IRMA, DPC’s Coat-A-Count® iPTH IRMA, Roche’s Elecsys® iPTH ICMA, and DSL’s Active® iPTH IRMA.

Results: Method comparison showed considerable interassay differences in the measurement of iPTH in ESRD patients. IPTH values assessed by other methods ranged, on average, from 60% to 152% of the Nichols Allegro IRMA values. Of the 6 iPTH assays tested, only the Scantibodies Total Intact PT IRMA (P = 0.7554) and the Roche Elecsys iPTH ICMA (P = 0.1327) resulted in iPTH values not statistically different from those obtained with the Nichols Allegro iPTH IRMA.

Conclusions: Noncomparability among iPTH assays remains a distinct problem for the management of ESRD patients. These results should be taken into consideration when determining the course of medical treatment based on measured iPTH concentrations

Parathormone response to thyroid surgery

BACKGROUND

Confident determination of adequate residual parathyroid function early after thyroid surgery could facilitate the discharge of patients soon after their operation without the need for subsequent serum calcium monitoring and/or calcium and vitamin D supplementation.

METHODS

Thirty-one patients who underwent 33 thyroid operations (22 unilateral lobectomies and 11 bilateral thyroid resections) were prospectively studied. Parathormone (PTH) levels were measured intraoperatively, and serum calcium was monitored before and after surgery to determine PTH and calcium homeostatic response to thyroid surgery.

RESULTS

A significant decrease in circulating PTH occurred during 27 procedures, most markedly after specimen mobilization. Intraoperative PTH and postoperative calcium levels were lowest in those who underwent bilateral operations. Patients who underwent unilateral procedures experienced significant decreases in PTH but not postoperative calcium levels. A PTH level >50% of baseline predicted normocalcemia by postoperative day 3. However, PTH level did not accurately triage other patients' risk for postoperative hypocalcemia.

CONCLUSIONS

A decrease in PTH levels intraoperatively is a common event during both unilateral and bilateral thyroid operations. Although normal PTH levels at the end of surgery ensure normocalcemia after surgery, patients with low final PTH measurements may not develop significant hypocalcemia after surgery.

Diagnosis of primary hyperparathyroidism: controversies, practical issues and the need for Australian guidelines

Primary hyperparathyroidism (PHPT) is one of the most common endocrine disease processes, however the clinical presentation in 2003 is typically characterized by minimal signs or symptoms of hypercalcaemia or para-thyroid hormone (PTH) excess. Recent developments in imaging and management of PHPT have been published, however the area of biochemical investigation has been relatively neglected. A group of experts convened in April 2002 to consider whether changes were needed to the 1990 consensus guidelines which defined criteria for the diagnosis and management of asymptomatic PHPT. It is appropriate to review the revised recommendations, which have been disseminated by the panel and were recently published. Each of the laboratory -analytes used to establish the diagnosis of PHPT and exclude alternative diagnoses or complications will be considered in succession in this review: (i) calcium, (ii) intact PTH, (iii) urinary calcium and (iv) 25 hydroxy-vitamin D. Furthermore, critical appraisal of the new diagnostic criteria and their applicability to Australian laboratories will be addressed. Finally, limitations and problems associated with the measurement of each analyte will be reviewed.

Intraoperative testing for parathyroid hormone: a comprehensive review of the use of the assay and the relevant literature

OBJECTIVE

The rapid intraoperative parathyroid hormone assay is transforming the parathyroidectomy procedure. We present a review of the literature on the use of the assay as an adjunct to surgery. To our knowledge, this is the first review of the literature to encompass and compare all known primary studies of this assay in parathyroidectomy patients.

DATA SOURCES

Articles were collected by searching MEDLINE databases using relevant terminology. The references of these articles were reviewed for additional studies. Supplementary articles pertinent to the parathyroidectomy procedure, preoperative parathyroid localization studies, and intraoperative parathyroid hormone assay development also were examined.

STUDY SELECTION AND DATA EXTRACTION

One hundred sixty-five references were analyzed and categorized separately into groups.

DATA SYNTHESIS

The primary studies of intraoperative data on patients undergoing parathyroidectomy were compared when possible. Studies were analyzed by type of assay used, where performed, turnaround time, and efficiency of use. Reviews of the types of parathyroid surgery and preoperative localization were included for educational purposes.Conclusions.-The intraoperative parathyroid hormone assay is a useful adjunct to preoperative imaging and parathyroid surgery because of its unique ability to detect an occult residuum of hyperfunctioning parathyroid tissue. Use of this assay will obviate the need for frozen section in most routine cases. The test facilitates minimally invasive parathyroidectomy for single parathyroid adenomas, which, in turn, improves cost-effectiveness and cosmetic outcome. Its use in patients with known preoperative multiglandular disease is promising but requires further study.

Kinetic analysis of the rapid intraoperative parathyroid hormone assay in patients during operation for hyperparathyroidism

BACKGROUND

Rapid intraoperative parathyroid hormone (RI-PTH) assay is used to guide adequacy of resection during operation for hyperparathyroidism. We compared the RI-PTH assay (15 minutes) with a standard PTH assay, determined whether the PTH half-life varied between patients, and constructed a kinetic analysis of the RI-PTH data.

METHODS

Forty-five patients with hyperparathyroidism had blood sampled at baseline and at times after parathyroid resection. Intact PTH was determined using RI-PTH and a standard assay. Values were fitted to an exponential decay curve using the baseline and the follow-up time points. PTH half-life and the new postexcision baseline value were calculated from the decay curve.

RESULTS

The RI-PTH assay and the standard PTH assay correlated well. Average PTH half-life was 1.68 +/- 0.94 minutes (0.42 to 3.81 minutes). A kinetic analysis yielded a formula for the generation of a PTH decay curve. Using a 50% reduction in RI-PTH at 5 minutes as the criterion for adequate resection, 2 patients were incorrectly classified as not being cured. These patients were correctly classified using the kinetic analysis.

CONCLUSIONS

PTH half-life can vary substantially. A kinetic analysis may be more accurate in assessing adequacy of resection. This method allows the surgeon to interpret RI-PTH data independent of the timing of samples.