PTH and vitamin D deficiency: Holler et al. studied 28 Fontan patients screened for vitamin D deficiency, finding significantly higher PTH levels in those with protein-losing enteropathy (PLE) (86.4 ± 33.3 ng/L vs. 43.2 ± 22.4 ng/L, respectively; p = 0.03) and more frequent hyperparathyroidism defined as circulating PTH levels of >72 ng/L (80% vs. 6.3%, respectively; p = 0.001) [74].