Study design and setting
In this cross-sectional study, we recruited 142 adult (age ≥ 18 years) consecutive patients who visited the diabetic follow-up clinic at Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia. The study was performed between August and November 2020.
Type 1 DM patients with diabetes duration of > 5 years or type 2 DM with any duration of diabetes were included in the study.
Because of the technical difficulty to do renal ultrasound examination, patients who are markedly obese (i.e., BMI > 40kg/m2, according to WHO criteria) were excluded from the study.
Renal artery stenosis, hypertension, heart failure, pregnancy and hydronephrosis were other exclusion criteria. In addition, patients who have acute complications, such as diabetic ketoacidosis, hyperglycemic hyperosmolar state, lactic acidosis, and hypoglycemia were excluded.
Age, sex, type of diabetes, duration of diabetes, weight, height, and other comorbidities of all patients were documented in a questionnaire.
Patients were evaluated by doppler ultrasound first then sent for laboratory investigations.
Urine protein measurement was performed by collecting a 24hr urine to measure urine protein concentration. Patients were instructed to collect urine starting in the morning. The first (overnight) urine on day 1 was discarded. All urine passed during the day and night will be included in the collection bottle. The first (overnight) urine on day 2 was included.
Moderately increased proteinuria defined as 24-h urinary protein excretion rate between 150 and 500mg⁄day and severely increased proteinuria as protein excretion rate > 500mg/day.
Serum creatinine was determined. Creatinine was measured using the Jaffe method. Calibrators and reagents are from Abbott and IDMS traceable.
To estimate glomerular filtration rate from serum creatinine, we used the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) Eq. (8), GFR (mL/min/1.73 m2) = 141 * min (Scr/k, 1) α *max (Scr/k, 1) −1.209 *0.993Age* 1.018(if female) * 1.159 (if black), where Scr is serum creatinine, k is 0.7 for females and 0.9 for males, α is − 0.329 for females and − 0.411 for males, min indicates the minimum of Scr/k or 1, and max indicates the maximum of Scr/k or 1.
Color Doppler ultrasound scan was performed by one radiology resident after he received training by the principal investigator. The first 10 examinations were performed under supervision. A 3-6MHz convex array transducer (Sonoscape ultrasound machine) was used for the examination. Patients were examined in supine position, the transducer placed in longitudinal axis, color doppler imaging was used to identify the segmental arteries and RI was collected in the segmental arteries two times in each the upper, middle and lower pole of both kidneys. The six values were averaged to obtain the mean RI for each side of the kidney. The average value between the right and left kidney was the RI used for analysis.
RI was calculated by the built-in software as follows: RI = (peak systolic velocity -end-diastolic velocity)/peak systolic velocity.
The threshold for an increased renal resistive index (RRI) is ≥ 0.70 for either right and or left RRI.
The research budget was limited to cover all the laboratory and other expenses; therefore, we applied a convenient sampling technique.
Ethical approval to conduct the study was obtained from Institutional Review Board of College of Health Sciences (058/19/Radio). Procedures were performed in accordance with the 1964 Helsinki declaration. All participants have provided informed consent.
Statistical analysis was conducted using Statistical Package for Social Science (SPSS) program version 25.0 (Chicago, IL, USA). The data presented as mean ± standard deviation (SD), median with interquartile range (IQR) or frequencies and percentages. Chi-square was used to see the association between categorical variables. Bivariate correlation among continuous variables was evaluated by Pearson’s correlation coefficient. Ordinal variables were evaluated by Spearman’s rho correlation. A regression analysis was performed to determine more related variables for the dependent variable (RI). Area under the ROC curve (AUC) of the receiver operating characteristic (ROC), sensitivity, and specificity were calculated to assess the significance of diagnostic value for RI. P- value less than 0.05 was considered significant.