Near infra-red interactance for longitudinal assessment of nutrition in dialysis patients.
OBJECTIVE
Serial nutritional assessment of dialysis patients is important because of the high incidence and prevalence of malnutrition in these patients. Near-infrared interactance (NIR) technology may provide a practical and reliable method to evaluate body fat and its changes over time in dialysis patients.


DESIGN
Longitudinal study consisting of 2 cross-sectional measurements, 2 months apart.


SETTING
Outpatient dialysis unit affiliated to a tertiary care community medical center.


PATIENTS
Seventy-one dialysis patients (35 men, 36 women), 57 +/- 15 years old, who have been on dialysis between 5 months and 11 years (43 +/- 30 months). Twelve additional patients with similar features were studied during the second round.


INTERVENTION
None.


MAIN OUTCOME MEASURES
NIR was used to estimate the body fat percentage. Other simultaneous measurements included subjective global assessment, anthropometric indices including midarm circumference, triceps and biceps skinfold thickness, and body mass index, and some laboratory values including albumin, transferrin, and cholesterol. NIR measurement was performed by placing a Futrex sensor on the nonaccess upper arm for several seconds, after logging the required individual data (sex, weight, height, and body frame), along with uniform physical activity levels for all patients, into a mini-computer.


RESULTS
Seventy-one dialysis patients underwent nutritional and laboratory measurements. A second measurement round was performed 8 to 9 weeks after the first one and included 12 additional patients. Within each cross-sectional round, Pearson correlation coefficients (r) between the NIR score and nutritionally relevant variables were significant for anthropometric values (0.56 to 0.82) as well as low cholesterol and creatinine (0.22 to 0.30). The two serial NIR measurements on the same patients were highly consistent over the 2-month study interval (r = 0.96), whereas anthropometric values showed greater variability. The within-person coefficient of variation for NIR was low, indicating high consistency between 2 measurements. Moreover, the timing of the NIR measurement (predialysis v postdialysis) did not have any impact on consistency of the NIR results. The longitudinal changes of NIR had significant correlations with anthropometric and laboratory changes over time.


CONCLUSION
The NIR, which can be performed within seconds, may serve as a reliable and practical tool for objective measurements of nutritional status in hemodialysis patients. The NIR not only seems to have a high degree of reproducibility but may also be an optimal tool to detect longitudinal changes in body fat over time. The NIR measurement is independent of the fluid status in dialysis patients. More comparative and longitudinal studies are needed to confirm the validity of NIR measurements in longitudinal evaluation of dialysis patients.