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Endocrine Abstracts (2016) 44 CC4 | DOI: 10.1530/endoabs.44.CC4

SFEBES2016 Featured Clinical Cases Featured Clinical Cases (10 abstracts)

Asymptomatic elevated PTH level due to immunoassay interference resulting from Macro-PTH: a case report

Paul Prodan , Eka Nandoshvili , Craig Webster & Jayadave Shakher


Heart of England NHS Foundation Trust, Birmingham, UK.


Introduction: Immunoassays are important tools in the diagnosis and management of disease; however, they are not free from interference by cross-reacting substances. Discordant clinical evidence and laboratory results raised suspicion of interference in a patient with persistently raised parathyroid hormone.

Case Presentation: Case description: A 56-year-old Caucasian female previously diagnosed with hypothyroidism consistently demonstrated elevated PTH levels with normal renal function, calcium and vitamin D concentrations. There was no clinical evidence of hyperparathyroidism and imaging of thyroid and parathyroid showed no evidence of pathology.

Results: The PTH levels were persistently elevated as measured by 2 different methods. (Roche and Abbott). PTH concentrations increased on dilution (base sample 28.5 pmol/l, 1:2 dilution 47 pmol/l). After treatment of the sample with polyethylene glycol (PEG) the PTH concentration decreased to 10.2 pmol/l. On dilution of the PEG treated sample, the diluted concentration was 12.1 pmol/l, demonstrating an appropriate response to dilution. These results indicated the presence of a Macro-PTH.

ROCHE PTH
Reference range: (1.6 – 7.2 pmol/l)
ABBOTT PTH
Reference range: (1.6 – 7.2 pmol/l)
Oct 2012122.5 pmol/lJan 2016126.9 pmol/l
Dec 2012195.8 pmol/l
Feb 2013143.7 pmol/l
July 2013165.6 pmol/l

Conclusion: Macro-PTH is PTH bound to an immunoglobulin molecule, which prevents its clearance by the kidneys and thus increased half-life. These molecules are usually not biologically active. Interference should be sought when there is lack of clinical correlation with immunoassay hormone levels.

Volume 44

Society for Endocrinology BES 2016

Brighton, UK
07 Nov 2016 - 09 Nov 2016

Society for Endocrinology 

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