PTH and hyperparathyroidism: Khan et al.24 found that PTH serum levels were significantly higher in the IF group; however, multivariable models did not identify this as an independent association, possibly because it is a covariate with low levels of serum calcium and vitamin D. Louazon et al.21 identified that patients displayed a relative hyperparathyroidism: PTH levels were within the normal range, but significantly higher in patients as compared to controls (256% of controls; p=0.003).