Endocrine Abstracts

Background: Iron overload disorders (IOD) are associated with a higher occurrence of unbalanced calcium (Ca)-phosphorous (P) metabolism, including hypoparathyroidism (HPT). However, data about prevalence and presentation of HPT in this setting are scanty. A Ca/P ratio <2.32 has been proposed to detect HPT in the general population.

Aim: To characterize Ca-P homeostasis, particularly the prevalence of HPT, in a cohort of adult patients with IOD compared to healthy subjects. Furthermore, the performance of Ca/P ratio in identifying concealed forms of HPT in IOD patients was tested.

Methods: A single-center, cross-sectional, case-control study was carried out including 58 IOD patients (39 patients with β-thalassemia (β-T) and 19 patients with hereditary hemochromatosis (HH)) and 76 controls. The main outcomes were: serum Ca, P, Ca/P ratio and intact parathyroid hormone (PTH). Primary hypoparathyroidism (pHPT) was defined as hypocalcemia with low/inappropriately normal PTH, whereas subclinical hypoparathyroidism (sHPT) as serum Ca at the lower limit of normal range with low PTH.

Results: IOD patients had lower serum Ca (P=0.032), higher serum P (P=0.004) and lower Ca/P ratio (P<0.001) compared to controls, whereas no difference was found for serum PTH. Patients with β-T had higher serum P (P<0.001), lower Ca/P ratio (P<0.001) and lower serum PTH (P<0.001) compared to patients with HH and controls, whereas no difference was found for serum Ca among subgroups. On the other hand, Ca/P did not significantly differ comparing HH and controls. pHPT was found in 6 patients with β-T (15.4%) and in none patients with HH; sHPT was found in 19 patients with β-T (48.7%) and in 1 patient with HH (5.3%). IOD patients with HPT showed lower Ca/P ratio (P<0.001) compared to IOD patients without HPT. A Ca/P ratio <2.32 allowed the correct identification of 19 out of the 26 IOD patients with overt or sub-clinical HPT (sensitivity 73.1%; specificity 87.5%). IOD patients with Ca/P ratio <2.32 had an almost 20-fold increased likelihood to be affected by HPT (OR 19.0 [4.9-74.0]; P<0.001).

Conclusions: Despite a low prevalence of overt pHPT, the non-classical phenotype sHPT seems to be a common finding in IOD patients. The Ca/P is useful to detect HPT even in this context. A periodic evaluation of serum Ca and P should be included in the follow-up of these patients to early detect an unbalanced mineral metabolism.