Estimated dietary sodium intake in peritoneal dialysis patients using food frequency questionnaires and total urinary and peritoneal sodium losses and assessment of extracellular volumes.

Abstract

Peritoneal dialysis (PD) patients are advised to restrict sodium intake. For best use of resources, rapid screening tools are required for dietary assessments to allow for targeting of patients. We wished to evaluate the usefulness of food frequency questionnaires (FFQ) for estimating dietary sodium. Sodium intake was estimated using the Derby Salt Questionnaire (DSQ), and Royal Free Sodium Questionnaire (RFSQ). Body composition was determined by bioimpedance. 90 peritoneal dialysis patients, 52 men (57.8%), mean age 62 ± 15.8 years, were asked to complete the DSQ and RFSQ questionnaires. 88 completed one or more questionnaire, with 87 completing the DSQ and 86 the RFSQ. The median estimated dietary sodium intake 104 (72-145) mmol/day (2.39 (1.64-3.34) g sodium/day) DSQ, and 92 (60-114) mmol/day (2.11 (1.38-2.62) g sodium/day) RFSQ. Younger patients, aged ≤52 years had greater dietary sodium intake compared to those ≥76 years (RFSQ 105.4 (73-129) vs 96 (71-116) mmol/day), p < 0.05. Extracellular water to total body water (ECW/TBW) was greater in those with higher DSQ estimated dietary sodium intake (0.40 ± 0.01 vs 0.39 ± 0.01, p < 0.05). A multivariable model showed that increased dietary sodium intake was independently associated with increased SMM (DSQ odds ratio (OR) 1.17 (95% confidence limits 1.05-1.32, RFSQ OR 1.15 (1.04-1.27, p < 0.05) and raised ECW/TBW (DSQ OR 1.88 (1.22-2.92) p = 0.004, and ECW/height (RFSQ OR 1.42 (1.02-1.98) p = 0.04. Both questionnaires were acceptable to patients, and the majority were found to be consuming more dietary sodium than recommended. Dietary sodium estimation was associated with SMM and increased ECW.