Falsely elevated plasma parathyroid hormone level mimicking tertiary hyperparathyroidism.

OBJECTIVE

To report a case of misdiagnosed tertiary hyperparathyroidism attributable to heterophile antibody interference in a parathyroid hormone (PTH) assay.

METHODS

We present clinical and laboratory data relative to this case and review the pertinent English-language literature.

RESULTS

A 36-year-old woman with a functioning renal allograft, PTH excess (3,374 pg/mL) refractory to medical therapy, and a history of renal osteodystrophy presented for consideration of a third parathyroidectomy. Remedial parathyroidectomy was performed. The PTH levels did not decline postoperatively, but the patient developed severe hypocalcemia. Reanalysis of the patient's serum specimens was performed with (1) addition of heterophile blocking agents to the murine-based immunoassay and (2) use of a different, goat antibody-based immunoassay. The true PTH level was found to be 5 pg/mL with use of both methods.

CONCLUSION

Previous administration of muromonab-CD3 (Orthoclone OKT3) for immunosuppression may have resulted in the development of human antimurine heterophile antibodies, causing a falsely elevated PTH result.