Body Mass Index (BMI), Kt/V and survival on hemodialysis

Although expression of hemodialysis dosing as Kt/V allows for the normalization of patient's size and body habitus variance, a recent study (Ann Intern Med 128:451, 1998 ) suggests that under the current dialysis practice a minimum Kt/V of 1.2 may be difficult to achieve in many overweight (OW) patients. Whether this has any influence on OW patients' survival is uncertain at present. In this study, we examined the effect of BMI on delivered Kt/V in 1226 patients on chronic hemodialysis (90% black, 10% Caucasian, 55% female) and determined the influence of these variables on 1-yr survival. 38% of the patients were OW, 13% were underweight (UW, BMI <20) and 49% were normalweight (NW, BMI 20-27,5). Kt/V was calculated as the mean of 2 months measurements. Kt/V correlated negatively with BMI (r -0.285, p<0.01). Kt/V in UW, NW and OW were 1.61 ± 0.02, 1.60 ± 0.01 and 1.36 ± 0.01*, repectively (m±SE, *p<0.01 than the rest). Using a 1.2 Kt/V cut off, 24% of OW patients were found to be underdialyzed (p<0.01 vs. the rest) compared to 14 and 7% in NW and UW categories. Interestingly, the patients with lower Kt/V, in addition to having higher BMI, also had significantly higher serum albumin and creatinine, both markers of better nutrition. In Cox proportional univariate analysis, BMI had significant positive impact on survival in whole patient population. In the subgroup analysis, UW patients, who happened to have the highest Kt/V, had the lowest survival compared to OW and NW groups. In Cox proportional univariate analysis, unlike BMI Kt/V had no influence on over all patient survival. However, in the subgoup analysis, Kt/V had positive influence on the survival of OW patients (0.27, 0.09-0.85, p<0.02),but not on NW and UW patients. The data suggest that UW patients are likely to die despite higher Kt/V, whereas insuring adequate dose of dialysis in OW patients may further increase their survival.