Falsely elevated parathyroid hormone in a patient with osteoporosis: a case report and review.

BACKGROUND: Parathyroid hormone (PTH) measurements can be falsely elevated due to the hormone binding to other molecules (macro-PTH) or immunoassay interference with heterophile, human anti-animal or other antibodies. This is rare but could lead to incorrect diagnosis, unnecessary investigations or avoidance of teriparatide treatment. We report a case of falsely high PTH levels due to assay interference and review the literature on cases of spuriously elevated PTH. CASE REPORT: An 87-year-old woman attending our bone health clinic with osteoporosis had persistently elevated PTH (383-784 pg/ml) using the Roche Cobas e801 immunoassay despite having normal serum calcium, phosphate, 25 hydroxyvitamin D (> 50 nmol/l) and eGFR (> 60 ml/min). To rule out falsely elevated PTH, a polyethylene glycol precipitation (PEG) test was performed which recovered less than 10% of the hormone resulting in a normal level. PTH was also tested on a different assay (Atellica Siemens) that identified a result of 27 pg/ml. The findings were consistent with immunoassay interference likely due to heterophile antibodies giving rise to a spuriously high PTH. DISCUSSION: The presence of unexpectedly high PTH levels should alert physicians to the possibility of false results due to assay interference or macro-PTH. This highlights the importance of clinically correlating results and of good communication with the testing laboratory. Here, we present the case of an 87-year-old woman with spuriously elevated PTH levels due to immunoassay interference likely mediated by heterophile antibodies. The presence of unexpectedly high PTH levels should prompt consideration of the possibility of false results due to assay interference or macro-PTH.

Sweat testing in the modern era: A national survey of sweat testing practice in the Republic of Ireland.

BACKGROUND: The sweat test has been the "gold standard" diagnostic test for cystic fibrosis for more than 40 years. We hypothesized that there would be a change in the pattern of sweat testing in Ireland since the introduction of cystic fibrosis newborn screening in 2011, when practices were last reviewed. This is a follow up survey looking at sweat testing numbers and practices. METHODS: A national survey compiled data on sweat collection, conductivity and sweat chloride testing in all hospitals previously identified as performing sweat tests. RESULTS: All 13 centres in Ireland performing sweat testing in 2018 responded to the survey (100% return rate). Our results indicate that 1007 sweat tests were performed in 2018 compared to 2555 in 2011, equating to a 61% reduction. Seven out of 13 centres are performing less than 50 sweat tests per year. Nine out of 13 centres (69%) had a sweat test failure rate greater than the recommended allowable rate of ≤ 10%. We detected a trend of sweat testing in patients with an existing diagnosis of CF who had commenced cystic fibrosis transmembrane conductance regulator (CFTR) modulators. CONCLUSIONS: There has been a significant reduction in the number of sweat tests performed in Ireland since the introduction of newborn screening for CF. There remains a lack of standardisation in many aspects of the service ranging from sample collection to reporting of results. We have identified a new trend of sweat testing in the cystic fibrosis transmembrane conductance regulator modulator era.