Diagnosing Primary Hyperparathyroidism in Pregnancy: A Case of Altered Parathyroid Hormone Degradation in Pregnancy

Diagnosing primary hyperparathyroidism in pregnancy is difficult due to pregnancy-related changes in parathyroid hormone (PTH); calcium; 1,25 vitamin D; and renal calcium excretion. Parathyroid hormone-related peptide (PTHrP) produced by the placenta adds additional complexity. Our case is the first to demonstrate an increased rate of PTH degradation within a pregnant individual who returned unexpectedly low PTH levels. We describe a 27-year-old female patient who presented at 25 weeks gestation with pancreatitis and hypercalcemia. Primary hyperparathyroidism was suspected but variable PTH results led to uncertainty and an assay error was considered. PTH samples were collected in both serum-separating tubes (SST) and EDTA tubes and compared to controls (5 nonpregnant and 5 pregnant individuals). Samples were retested every 2 hours for a period of 10 hours. A rapid decline in the measured PTH was noted in the index case, an observation which differed from controls. We postulated that internal and/or external factors influenced the PTH measurement obtained from our patient. From our observations, rapid PTH degradation in pregnancy, and individual variation in PTH stability and laboratory processes, can influence PTH results and impact on interpreting hypercalcemia in pregnancy.