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Body mass index (BMI) evaluation is very important in chronic kidney disease (CKD) patients, as a screening tool. According to WHO(1) overweight (BMI 25 a 29,9 Kg/m2) and obesity (BMI ≥30 Kg/m2) increased the mortality risk vs normal weight (BMI18,5 a 24,9 Kg/m2), among the general population. In the oldest persons, this relation changes and the least mortality risk is associated with the highest BMI (22-26.9 Kg/m2)(2) . In CKD 5D patients an inverse association has been described, but in earlier CKD stages it is not well defined. The Uruguayan National Renal Healthcare Program (NRHP-U) registry included CKD adult patients stages 1-5 no D, median age 70 years.
The aim of the study was to evaluate, in the NRHP-U CKD cohort, the association between BMI and mortality (all-causes and cardiovascular), according to age and CKD stages.
A retrospective analysis of the NRHP-U CKD patients was done. The registry included patients 19 years or older, with weight and height data. The variables studied were sex, age, CKD stage, proteinuria, blood pressure, diabetes, smoking, and cardiovascular comorbidities. Follow-up time was calculated between NRHP-U inclusion and the final date (death date, kidney replacement therapy starting date, or June 30th, 2023). BMI were categorized in: <18.5, 18,5 a 22.49, 22.5 a 24.99, 25 a 27.49, 27.5 a 29.99, 30 a 32.49, 32.5 a 34.99, 35 a 37.49, 37.5 a 39.99 y ≥ 40 Kg/m². The Hazard Ratio (HR) risk for all-cause and cardiovascular death was calculated with the Cox proportional risk model adjusted to the above-mentioned variables. Each BMI category HR was calculated with the lower risk category as the reference. All patients signed informed consent and the study was approved by the Ethics Committee.
There were included 21183 patients, mean age (pc 25-75) 70 years (60-77), male sex 58%, CKD stage 1, 2, 3, 4 y 5 (%): 6.6, 11.5, 58.5, 19.7 y 3.1%. Proteinuria/albuminuria < 0.3 gr/day: 78.8%, between 0.3 y 0.99 gr/d: 10.7% and ≥ 1 gr/d: 9.0%. Diabetes: 38.3%, smoking: 6.8%, cardiovascular comorbidity: 30.2%, systolic blood pressure (SBP) < 120 mmHg: 17.2%, 120 - 139 mmHg: 42.3%, BMI: <18.5: 0.9%, 18,5 a 22.49: 8.2%, 22.5 a 24.99: 13.6%, 25 a 27.49: 18.5%, 27.5 a 29.99: 18.9%, 30 a 32.49: 15.5%, 32.5 a 34.99: 10.3%, 35 a 37.49: 5.8%, 37.5 a 39.99: 3.3% y ≥ 40 Kg/m²: 5%. Follow-up time, median 5.71 years (pc25-75: 3.33 – 9.58). All-cause death: 8.025 (37.9%) (rate 6.0/100 pts-year), cardiovascular deaths 2353 (11.1%), rate 1.76/100 pts-year. The BMI categories with lower all-cause and cardiovascular death risk are shown in Table 1. The BMI category 27.5 and 32.49 Kg/m² showed a significantly lower all-cause mortality risk (Figure 1) In the group older than 70 years, the lower death risk is associated with a BMI of 30 to 32.4 Kg/m². significantly different from the highest (BMI ≥ 37.5 Kg/m²: HR 1.23) and the lowest categories (BMI < 25 Kg/m²: HR 1.38).
In the Uruguayan CKD 1-5ND patient cohort, a BMI between 27.5 and 32.49 Kg/m², was associated with the lower all-cause and cardiovascular death risk.