Endocrine Abstracts

Introduction: Macrohormones are complexes of monomeric hormone molecules with IgG leading to formation of macrocomplexes. They are usually immunoreactive, but biologically inactive. The higher molecular weight results in reduced renal clearance and therefore accumulation in the blood. We present two cases of unusual macrohormones.

Case 1: A 55-year-old male had his thyroid function checked as part of investigation for chest pain, and was started on thyroxine on finding of TSH at 36 mU/L (0.35–5) with FT4 at 10 pmol/L (9–22). He developed flushing and general discomfort whilst on thyroxine, which was discontinued. Subsequent analyses showed consistently elevated TSH and low normal FT4. Since he was clinically euthyroid analytical interference was considered a potential cause of high TSH. Implementation of polyethyleneglycol (PEG) precipitation protocol gave recovery rate at 30.9%, suggestive of macro-TSH.

Case 2: A 72-year-old male, with a history of renal transplantation, recovering from recent influenza-A pneumonia, was reviewed in the Renal Clinic. Blood tests revealed PTH at 506 pmol/l (1.6–7.5), confirmed on repeat sample, with normocalcaemia and vitamin D insufficiency. His PTH had previously been between 26–48 pmol/l. His clinical presentation was inconsistent with a severely hyperparathyroid state. Treatment of serum with blocking reagents did not detect heterophilic antibodies. Analysis on two different analytical platforms gave discordant results. Another sample was subjected to PEG extraction: PTH was reduced from 297.9 to 61.38 pmol/l (recovery rate 20.6%), and decreased linearly following serial dilutions. These suggested the presence of macro-PTH, likely attributed to anti-influenza antibodies.

Conclusions: Discrepancies between clinical findings and laboratory results should raise the suspicion of analytical interference. Presence of macro-complexes is a type of interference, with PEG precipitation being a technically simple, yet efficient method to detect it.