Impact of salt restriction on renal function, urine protein–creatinine ratio and nutrition of patients with chronic kidney disease stages III–V

Abstract

Methods: We enrolled 48 hypertensive patients with CKD into one-month dietary modification with salt restriction and without alteration in antihypertensive medication. We measured timed urine collection of urinary sodium (Na) to estimate the dietary salt intake; urinary protein–creatinine ratio (UPC), eGFR and creatinine clearance. After the intensive dietary modification, antihypertensive medication was adjusted to aim blood pressure below 130/80 mm Hg and patients were followed up for a year. Results: 9 were female and 39 were male; 28 patients have type 2 diabetics. Age ranged from 30 to 88 with mean of 62 years. Mean 24-h urine creatinine clearance was 27.4±standard error 1.9 mL/min/1.73 m2; 15, 26 and 7 patients were in CKD stages III to V. Only 17 patients (35%) (Group A) managed to reduce 24-h urinary Na excretion below 100 mmol/day, from mean of 135±15 to 64±5 mmol/day. Another 31 patients (Group B) who could not, increased 24-h urinary Na from 153±12 to 202±13 mmol/day. In 31±1 day, mean, systolic and diastolic BP (MBP, SBP, DBP) reduced from 102±1 to 99±2 (P=0.044), 149 to 142 (P=0.013), 79 to 78 mm Hg (P=0.362). In a 1 year follow-up, blood pressure was 135±4/77±3 mm Hg in Group A while 139±3/77±2 mm Hg in Group B (P=0.357 and 0.942). Both groups have same means of baseline eGFR, 27 mL/min/1.73 m2. Over the next 1-year follow-up, Groups A and B have dropping eGFR of −4.1±0.9 vs −1.3±1.1 mL/min/1.73 m2/year (P=0.096). Anyway, Group A has higher initial UPC: 225±50 mg/mmol which reduced to 166±42 mg/mmol (P=0.005) in follow-up while Group B has mild reduction from 181±46 to 161±34 mg/mmol (P=0.536). Albumin level of both groups maintained well at mean of 42 g/L eventually. Both groups have same baseline body mass index around 26 kg/m2. However, in a-year follow-up, group A has a slower weight decrease than group B, i.e. −1.4±1.2 vs −7.1±3.4 kg/year. Four patients met combined end point of death, doubling creatinine and dialysis: 1 (6%) of Group A and 3 (10%) of Group B (P>0.05). Conclusion: Na restriction <100 mmol/day is a valuable but difficult to achieve target in hypertensive patients with CKD stages III–V. Lowering Na intake to <100 mmol/day may reduce UPC while maintaining good nutrition. However, the result may be affected by other confounding factors and changes in Na intake over time.