Unique classification of parathyroid dysfunction in patients with transfusion dependent thalassemia major using Nomogram-A cross sectional study.

INTRODUCTION

Hypoparathyroidism is a rare complication of iron overload in patients with transfusion dependent β thalassemia major (β-TM). We aim to determine the prevalence of parathyroid dysfunction in patients with β-TM.

METHODS

Diagnosed cases of transfusion dependent β-TM between 5 and 17 years of age were recruited from outpatient clinics of a non-profit organization in Karachi, Pakistan. Blood and urine samples were collected in fasting to determine Ca, P, Alb, Mg, Cr 25OHD and iPTH. Patients were grouped on the basis of upper and lower levels of Ca, 25OHD and iPTH for assessing parathyroid dysfunction into primary hypoparathyroidism [], sub-clinical hypoparathyroidism [ normal functioning parathyroid gland [] and secondary hyperparathyroidism []. Using PTH nomogram subject specific expected PTH (maxPTH) was calculated. Difference between maxPTH and measured iPTH was determined to assess the utility of nomogram in identifying parathyroid gland dysfunction. The statistical analysis was performed using the Statistical Package of Social Sciences (SPSS) version 20.

RESULTS

Median age of patients was 11 years (13-7) with males being 54.2% (n = 205).Based on Ca, 25OHD and iPTH, primary hypoparathyroidism was identified in 3.4% (n = 13) [median iPTH 11.3 pg/ml (12.6-7)], 52.3% (n = 192) had subclinical hypoparathyroidism [iPTH 40.4 pg/ml (52.7-28.7)], and 34% (n = 125) were identified as secondary hyperparathyroidism [iPTH 88.6 pg/ml (116-74.7)]. Normal response to Ca & 25OHD was seen in 10.6% (n = 39) [iPTH 44.2 pg/ml (53.8-33.4)] patients. High phosphorous was present in all groups. Difference between maxPTH & iPTH was highest in primary hypoparathyroidism, followed by subclinical and secondary hyperparathyroidism.

CONCLUSION

Nomogram by Harvey et al. identify low secretion capacity of parathyroid gland that correlated with biochemical classification of patients. It requires clinical validation before using in clinical practice for assessing parathyroid dysfunction.