Role of Calcium and Phosphate Ionic Product as an Early Marker of Vascular Calcification to Predict Cardiac Risk in Chronic Kidney Disease: A Case-control Study

Abstract

Introduction: Cardiovascular disease is the most leading cause of death in patients with Chronic Kidney Disease (CKD) and Vascular Calcification (CV) is one of the strongest predictors of cardiovascular risk. CV is a process characterised by thickening and loss of elasticity of muscular arteries walls which occurs in two distinct sites, the intimal associated with atherosclerotic plaques and medial calcification is characterised by vascular stiffening and arteriosclerosis with adverse clinical outcomes leading to cardiovascular mortality. Disturbed mineral metabolism such as increased serum phosphorus and ionic product may be one such risk factor and is emerging as a principle modifier of CV in the CKD subjects. Aim: To determine serum phosphorus and calcium in CKD patients and compare with calcium phosphorus ionic product as an early independent marker of CV in CKD to predict cardiac mortality. Materials and Methods: This was duration based case-control study conducted in Department of Nephrology, Vydehi Institute of Medical Sciences & Research Centre, Karnataka, India. Fifty cases of CKD presented in stage 3,4 and 5 and 50 healthy individuals between the age group 21-78 years were included as controls. Serum levels of Calcium, Phosphorous were analysed in autoanalyser, Ca x P ionic product was calculated, estimated Glomerular Filtration Rate (eGFR) was calculated by Modification of Diet in Renal Disease (MDRD) formula. All measured variables were compared with eGFR and compared between cases and controls. The results were presented as a mean±Standard Deviation (SD) and p-value <0.05 was considered as significant. Results: Mean age of cases were 47.74±11.01 years and 45.66±11.46 years were of controls. Clinically, confirmed CKD was found more in male patients 31 (62) compared to female 19 (38). eGFR (mL/min) cases (14.12±10.72) and (102.97±27.46) in control, Serum Creatinine (mg/dl) were 7.04±5.34 mg/dL in cases which was significantly more compared to control (0.84±0.20 mg/ dL). Serum Calcium (Ca) (mg/dL) 8.11±1.09 mg/dL in cases less compared with control 9.31±0.42 mg/dL, indicating hypocalcaemia. Serum Phosphrous (P) 5.2932±1.83 mg/dL) in CKD suggesting hyperphosphatemia compared to control (3.27±0.54 mg/dL). Calcium Phosphorus Ionic Product was 46.9108±14.77 in cases, elevated in CKD as compared to control (30.46±5.03). Statistically, significant result was found between serum phosphorus and calcium phosphorus ionic product (p<0.05), well compared with eGFR of stage 3, 4 and 5 CKD patients. Conclusion: Hyperphosphatemia and elevated calcium- phosphate ionic product is an early independent marker of calcification to predict cardiovascular risk in late stages of CKD.