Normocalcemia but still elevated parathyroid hormone levels after parathyroidectomy

Abstract

Key Clinical MessageEven when laboratory results at first match with clinical assessment, assay interference should still be on a clinician's mind when later results no longer fit with the patient.

A case report of PTH elevation due to immunoassay interference

“…In particular, urine calcium was 124 mg/24 h; phosphatase alkaline was 92 U/L, bone phosphatase alkaline was 12.6 µg/L, and c-terminal telopeptide was 0.26 ng/mL. DEXA of the lumbar spine (L1-L4) showed a BMD of 1.4 g/cm 2 , with T-score of 2.8 and Z-score of 3.6, and DEXA of the proximal femur (neck) showed a BMD of 0.8 g/cm 2 , with T-score of − 0.7 and Z-score of 0.3. Parathyroid imaging (dual-phase scintigraphy and ultrasound) did not show any abnormality.…”

“…There are only a few reports of PTH elevation due to immunoassay interferences [1][2][3][4]. The most common cause accounting for it is represented by heterophile antibodies, which are found in 30-40% of serum samples, and lead to falsely elevated laboratory results in 0.5-3% of the cases.…”