Background: Patient with stage 3 or 4 chronic kidney disease (CKD) usually has normal level of serum phosphate, due to increased serum fibroblast growth factor-23 (FGF23) level that resulted in increased phosphate urine excretion. On the other hand, serum FGF23 elevation was related to CKD progression, vascular calcification, cardiomegaly, and mortality. This double blind, randomized controlled trial study was conducted to evaluate effectiveness and safety of calcium carbonate administration in stage 3 or 4 CKD patients with normophosphatemia.

Hypothesis: Calcium carbonate administration is effective and safe in chronic kidney disease (CKD) with normophosphatemia.

Cardiovascular disease is the most cause of mortality of chronic kidney disease (CKD) patients. As CKD progresses, the prevalence of cardiovascular disease also increased. Beside traditional cardiovascular risk factor that the investigators have known, some non-traditional cardiovascular risk factors were reported to be associated with cardiovascular disease in CKD patients, which one of them was increased level of fibroblast growth factor-23 (FGF23).[1,2]

FGF23 reduces production of 1,25-vitamin D3 and expression of sodium-phosphate cotransport, and also excretes phosphate through urine. In healthy and CKD population, increased phosphate level resulted in increased production of FGF23. Normophosphatemia state in early to moderate stage of CKD was reported due to body compensation by increasing the level of FGF23. On the other hand, increased serum FGF23 level was related to CKD progression, cardiomegaly, vascular calcification, and mortality.[1] There are several ways to prevent hyperphosphatemia, such as low phosphor intake, phosphate binder administration, and adequate dialysis.[3]

Phosphate binder was reported to give positive effects in CKD patients with hyperphosphatemia. Studies which investigated the use of phosphate binder in CKD patients with normophosphatemia to decrease FGF23 were still limited and the result was controversial.[1]

Therefore, this double blind, randomized controlled trial study investigated the effectiveness and safety of calcium carbonate in early to moderate CKD patients with normophosphatemia in lowering FGF23 levels. Study participant were randomized to receive calcium carbonate or placebo for 12 weeks. Before and after intervention, blood and urine sample were taken to examine serum FGF23, serum phosphate, urine phosphate, ionized calcium, serum calcium, urea, creatinine, estimated glomerular filtration rate (eGFR), and albumin. Effectiveness of calcium carbonate administration was indicated by serum FGF23, while safety was indicated by serum calcium.

Inclusion Criteria:

• Stage 3 or 4 chronic kidney disease patient that visit nephrology or endocrinology outpatient clinic of dr. Cipto Mangunkusumo Hospital
• Normal level of serum phosphate
• Agreed to join in this study

Exclusion Criteria:

• Subjects with BMI < 18.5 kg/m2 or > 30 kg/m2
• Consume drugs which may interfere bone mineral metabolism