Interference caused by anti-streptavidin antibodies in a parathyroid hormone assay; a case report

Endogenous antibodies can lead to test interference in streptavidin-biotin based laboratory assays, such as thyroid function tests or parathyroid hormone (PTH) levels. We report about a patient, who presented for thyroid surgery, showing undetectable PTH levels despite normocalcaemia in internally assessed preoperative laboratory work. Previously, anti-streptavidin antibodies were detected in the patient’s blood and normal PTH levels could be measured in a streptavidin-free assay. To our knowledge this is the first reported case of a clinically relevant PTH test interference due to endogenous anti-streptavidin antibodies, thus complicating the evaluation of postoperative hypoparathyroidism.