The Dilemma of the Normal Baseline Parathyroid Hormone Level using the Intraoperative PTH Assay

Identification of carboxyl-terminal peptide fragments of parathyroid hormone in human plasma at low-picomolar levels by mass spectrometry

For decades, researchers have tried to identify the primary structures of circulating carboxyl-terminal parathyroid hormone (C-PTH) peptide fragments that may be present at only picomolar levels in human plasma. Although immunoassays and radiosequencing techniques have provided valuable fragment characterizations, no analysis has successfully determined their exact primary structures. In this work, for the first time, four human C-PTH peptide fragments, hPTH(34-84), hPTH(37-84), hPTH(38-84), and hPTH(45-84), have been identified from human plasma using MS-based methods. C-PTH peptide fragments were isolated from plasma samples by immunoaffinity extraction. The eluate was analyzed by capillary LC fractionation followed by MALDI-TOF-MS or by on-line coupling of nano-LC with ESI-TOF-MS. Both the MALDI- and the ESI-based approaches were capable of detecting C-PTH peptide fragments in human plasma at <10 pmol/L. The MALDI-TOF approach was effective in preliminary searches for C-PTH peptide fragments, but the use of high laser power limited the resolution necessary for accurate C-PTH peptide identification. The high mass resolution (10,000) and accuracy (10 ppm) attained by the ESI-TOF approach enabled unambiguous identification of these peptides. The four C-PTH peptide fragments identified in plasma samples from patients with chronic renal insufficiency were also found in the plasma of healthy women receiving recombinant human PTH either by subcutaneous injection or by intravenous infusion. This newly developed analytical capability should greatly enhance the understanding of PTH metabolism and parathyroid gland function.

Effectiveness of parathyroid-hormone measurement in detecting patients with multiple gland disease causing primary hyperparathyroidism

BACKGROUND AND AIM

Intraoperative parathyroid hormone measurement (iPTH) has strengthened the successful use of minimal-invasive approaches in surgery of primary hyperparathyroidism (pHPT). The aim of the study was to evaluate the efficacy of iPTH monitoring in treating pHPT resulting from multiple gland disease.

MATERIALS AND METHODS

In this retrospective study, 58 patients with pHPT underwent surgery (minimally invasive or open exploration) between January 2003 and July 2005. iPTH levels were routinely measured at the start of anesthesia, in any case before skin incision, and 10 as well as 15 min after removal of abnormal gland(s). A drop in iPTH >50% after 10 min and >60% after 15 min was considered adequate to prove the success of the removal of the abnormal gland(s). The removed tissue was examined histologically by immediate frozen section.

RESULTS

A single gland disease was found in 51 (88%) cases, a multiple gland disease (double adenoma or hyperplasia) in 7 (12%) cases. In all cases of single adenoma, an adequate drop of iPTH was seen after removal of the pathologic gland. In contrast, in all cases with a second adenoma, an adequate drop in iPTH was detected only after removal of both adenoma/hyperplasia. Immediate sectioning was only helpful for identification of removed tissue, but was no help in deciding whether to search for an additional gland. The follow-up showed no late disease recurrence.

CONCLUSION

The measurement of iPTH is an effective and safe means in treating single gland disease as well as multiple gland disease (adenoma/hyperplasia) causing pHPT and also allows a successful limited dissection via minimally invasive parathyroidectomy.

A capillary-based microfluidic instrument suitable for immunoaffinity chromatography

The analysis of biological samples to produce clinical or research data often requires measurement of analytes from complex biological matrices and limited volumes. Miniaturized analytical systems capable of minimal sample consumption and reduced analysis times have been employed to meet this need. The small footprint of this technology offers the potential for portability and patient point-of-care testing. A prototype microfluidic system has been developed and is presented for potential rapid assessment of clinical samples. The system has been designed for immunoaffinity chromatography as a means of separating analytes of interest from biological matrices. The instrument is capable of sub-microliter sample injection and detection of labeled antigens by long wavelength laser-induced fluorescence (LIF). The laboratory-constructed device is assembled from an array of components including two syringe pumps, a nano-gradient mixing chip, a micro-injector, a diode laser, and a separation capillary column made from a polymer/silica (PEEKsil) tube. An in-house program written with LabVIEW software controls the syringe pumps to perform step gradient elution and collects the LIF signal as a chromatogram. Initial columns were packed with silica beads to evaluate the system. Optimization of the device has been achieved by measuring flow accuracy with respect to column length and particle size. Syringe size and pressure effects have also been used to characterize the capability of the pumps. Based on test results, a 200-microm x 25-mm column packed with 1-microm silica beads was chosen for use with a 500-microL syringe. The system was tested for mixer proportioning by pumping different compositions of buffer and fluorescent dye solutions in a stepwise fashion. A linear response was achieved for increasing concentrations of fluorescent dye by online mixing (R2=0.9998). The effectiveness of an acidic gradient was confirmed by monitoring pH post-column and measuring premixed solutions offline. Finally, assessment of detectability was achieved by injecting fluorescent dye solutions and measuring the signal from the LIF detector. The limit of detection for the system with these solutions was 10.0 pM or 10.0 amol on-column. As proof-of-principle, immunoaffinity chromatography was demonstrated with immobilized rabbit anti-goat IgG and a fluorescent dye-goat IgG conjugate as a model antigen.