Truly elevated PTH or Ulysses syndrome?

SUMMARY: An 11-year-old girl presented to the emergency department with hypophosphataemia. Subsequent investigations repeatedly demonstrated elevated serum parathyroid hormone (PTH) associated with normal serum total calcium, phosphate, vitamin D, and bone turnover markers. Imaging studies were initially interpreted as being consistent with the effects of hyperparathyroidism; however, follow-up review by specialists with paediatric expertise concluded otherwise. Further laboratory studies ultimately demonstrated that there was a false elevation in PTH, determined to be due to interference in the PTH assay from the formation of macromolecular complexes. This case highlights the effects of a phenomenon known as 'Ulysses syndrome', whereby a patient is sent on an unnecessary journey of extensive diagnostic investigation conducted because of a false-positive result. Recognition of macromolecular complexes and antibody interferences in patients with PTH results that are discordant with the overall clinical picture and other biochemistry results may prevent this phenomenon, with all its psychological and financial consequences.

LEARNING POINTS: PTH results that are discordant with the clinical picture or other biochemistry results should be suspicious for assay interference. Macro-PTH complexes and other antibody interferences are rarely reported, although they are a potential cause of spuriously elevated PTH. Recognition of potentially spurious results early can reduce unnecessary investigations and prevent potential misdiagnosis.