In this cross-sectional study, a total of 88 patients with ESRD on hemodialysis (HD) were recruited at hemodialysis centers of Shiraz University of Medical Sciences, Shiraz, Iran. The study protocol was reviewed and approved by the Ethics Committee of Shiraz University of Medical Sciences, Shiraz, Iran. The inclusion criteria were as follows: patients aged 17 to 65 years and receiving regular HD. We excluded the patients who received protein supplements or antibiotics currently or recently and those who were hospitalized or had infections within the 2 months prior to recruitment to the study. We screened 300 HD patients and 88 eligible patients were included and they signed the informed consent to participate in this study. Eligible patients were dialyzed with polysulfone/polyamide membranes, reverse-osmosis purified water, and bicarbonate-containing dialysate at least twice per week.
Sample size was determined according to a similar study assessing malnutrition prevalence considering different methods including SGA (8). A sample size of 88 patients was determined with a P of 0.05 and d of 0.01 at the predetermined level of alpha = 0.05.
At the beginning of the study, after assessing the demographic information of the patients, their nutritional status was assessed using three methods including SGA questionnaire, MUST questionnaire, and nPCR in order to classify the patients according to their nutritional status and compare the methods in assessing the nutritional status of these patients. First of all, SGA questionnaire was completed for each patients as it needs no laboratory measurement. The SGA is a comprehensive method for assessing malnutrition in various diseases including HD. This is an inexpensive and rapid method for assessing nutritional status in patients. No laboratory data is needed and this method is considered a valid tool for assessing nutritional status in hemodialysis patients as it was also used in different studies (4). This questionnaire was previously applied in different studies assessing the nutritional status of HD patients (3, 4). The questionnaire has different parts that assess various features including any changes in weight (during the preceding 6 months and 2 weeks), dietary intake, gastrointestinal problems, functional capacity, and any metabolic demand of the underlying disease were assessed. In the part related to the physical examination, the investigator assessed loss of subcutaneous fat, muscle wasting, and the presence of ankle/sacral edema. Each feature was separately rated as A, B, or C to demonstrate the degree of malnutrition. Then, we converted the SGA ratings to numerical equivalents: a score up to 10 indicates well-nourished; 10 to 17, at risk for malnutrition or mildly to moderately malnourished; and higher than 17 as severely malnourished (3, 4). In the present study, an experienced investigator working regularly with HD patients did the physical examinations needed and completed the SGA questionnaires.
In the next step, MUST questionnaire was completed for each patient by the main investigator. The Iranian version of this questionnaire was previously validated in a another study (12). One part of assessment in MUST questionnaire included calculating body mass index (BMI), hence, at the end of the dialysis session, dry body weight was measured using a digital scale with an accuracy of 0.1 kg while the patients were barefoot and wore lightweight clothes and their height was also measured in erect position via a stadiometer with an accuracy of 0.1 cm. For calculating BMI, body weight (kg) was divided by the height squared (m2). We also asked about the usual weight of patients in a period of three to six months. Another part was related to the percentage of unintentional weight loss in the previous three to six months and this was calculated from patients’ reports. In the next step in MUST questionnaire, acute disease effect was assessed and scored considering dietary intake and the presence of any acute disease, when the patient had any acute disease and has been or was likely to have no nutritional intake for 5 days, she/he would get a score of 2 from this part (11).
According to MUST scoring (Fig. 1), the studied patients were classified into three malnutrition risk categories (low, medium and high) as follows: Patients with the BMI of < 18.5 kg/m2 and a history of unintentional weight loss of > 10% in the last three to six months were considered as high risk for malnutrition; BMI 18.5–20 kg/m2 and a history of unintentional weight loss 5% − 10% in the last three to six months as medium risk; and BMI > 20 kg/m2 and unintentional weight loss < 5% in the last three to six months were considered as low risk (ie. normal or without malnutrition) (11). Overall, the final scores could classify the patients as low risk, medium risk, or high risk (Fig. 1).
For the last step, we decided to assess the nutritional status of the patients considering nPCR calculation. For calculating nPCR, some laboratory data were needed to calculate it using the following Eq. (13):
nPCR = (0.0136 × F) + 0.251 in g/kg per day
Where F is equal to Kt/V × ([predialysis BUN + postdialysis BUN]/2).
For calculating nPCR, pre and post BUN (blood urea nitrogen) and Kt/v were needed and we obtained them with the help of the nurses working with hemodialysis patients for the dialysis procedure. For obtaining pre and post-dialysis BUN, blood samples were taken from each patient before and after the dialysis session.
After centrifugation, serum was separated and stored and BUN was measured for each patient for twice (pre and post dialysis). Then, considering the BUN and Kt/v, the nPCR was calculated for each patient using the aforementioned equation. According to the nomenclature for protein-energy wasting (PEW) proposed by the International Society of Renal Nutrition and Metabolism in 2008, nPCR ≤ 0.8 could be considered a criteria for PEW in HD patients (13). In addition, serum albumin of all the patients were recorded from their medical history as it was measured recently at the time of the study. Considering the fact that we obtained serum albumin, nPCR, BMI, and serum Cr for all patients, we also assessed the presence of PEW according to all 4 criteria of the International Society of Renal Nutrition and Metabolism in all patients. These criteria include nPCR ≤ 0.8, serum albumin < 3.8 g/dl, BMI < 23 kg/m2, and serum Cr < 818 µmol/L. For assessing PEW, when no criteria was present, PEW were not existent, 1 criteria showed mild PEW, 2 criteria showed moderate PEW, and when 3 or 4 criteria were present, severe PEW were defined (13).
Moreover, we also calculated sensitivity, specificity, and precision for the three methods of assessment (SGA, MUST, and nPCR). Sensitivity is used to assess the strength of a test to detect true positive cases with malnutrition and specificity is used for detecting the true negative cases with malnutrition. Precision is the positive predictive value of a test.
Finally, the data were analyzed using SPSS software, version 22 (SPSS Inc.). Results are reported as percent or frequency for showing the prevalence of malnutrition according to different methods. Sensitivity, specificity, and precision rate for each test are shown in percentage. For comparing malnutrition between different methods, chi-square test was used. For assessing the correlation between different methods, Pearson correlation was used for the normal data and spearman correlation for the skewed data. P < 0.05 was considered significant.