The SA Journal Diabetes & Vascular Disease Volume 18 No 2 (November 2021)

SA JOURNAL OF DIABETES & VASCULAR DISEASE RESEARCH ARTICLE VOLUME 18 NUMBER 2 • November 2021 19 a period of 12 months. The study protocol was approved by the joint University of Ibadan and University College Hospital ethics committee, with the approval number NHREC/05/01/2008a. The minimal sample size was calculated using the equation for comparative observational studies: n = {4 θ ² [ Z α + Z (1– β )]²} D ² where n = minimum sample size, Z α = standard deviation of α at 95% confidence interval (= 1.96), Z β = standard normal deviate of β at 20% (= 0.842), θ = standard deviation of outcome of interest (= 0.11)12 and D = estimated difference in mean resistivity index between groups (= 0.10). Minimal sample size n = [4 × 0.11² × (1.96 + 0.842)²]/0.10² = 36 and with attrition of 10%, the minimal sample size for each arm is 40. Included in the first arm of the study were individuals older than 40 years with DM and evidence of DN. The second arm consisted of individuals older than 40 years with DM but without DN, while the third arm was healthy individuals older than 40 years. Excluded from the study were individuals less than 40 years of age, those with a single kidney, non-diabetic kidney disease, renal artery stenosis, ongoing urinary tract infection, urinary tract abnormalities, hypotension, bradycardia and haemoglobinopathy. Data were collected from all participants using a pre-tested questionnaire, and information obtained was sociodemographic details, lifestyle, medical history, history of DM and its duration, medication history and features of kidney disease. The height and weight were measured using standard stadiometers and weighing scales (SECA, UK). Body mass index (BMI) was calculated from the weight and height, while other anthropometric measurements taken were hip and waist circumferences. Three supine blood pressure recordings were taken and the average was recorded for every participant after at least 10 minutes’ rest. Early morning spot urine (10 ml) was collected from each participant for urinalysis and urinary albumin–creatinine ratio (UACR) assay. In addition, 10 ml of venous blood was collected for serum creatinine, glycated haemoglobin (HbA 1c ) and fasting lipid profile analysis. The eGFR was calculated using the CKD-EPI equation. 23 Pulsed Doppler analysis of the intrarenal arteries (interlobar arteries) was performed using a General Electric Logiq P5 ultrasound machine (General Electric Medicals, Ohio, USA) with a 2.5–5.0-MHz curvilinear transducer. Participants were scanned after an overnight or about eight-hour fast to minimise bowel gas shadows, which can obscure the kidneys. The peak systolic velocity (PSV) and end- diastolic velocity (EDV) were obtained from the interlobar arteries bilaterally using M-mode analysis. 24,25 Three to five reproducible waveforms from each kidney were obtained, and the RI from these waveforms was averaged to arrive at the mean RI value for each kidney (Fig. 1). Doppler examinations were carried out by the same experienced radiologist and this eliminated the possibility of inter- observer variability. DM was defined in accordance with American Diabetes Association (ADA) criteria. These criteria include the presence of symptoms of diabetes, along with a random plasma glucose concentration of ≥ 200 mg/dl (11.1 mmol/l), or fasting plasma glucose (FPG) of ≥ 126 mg/dl (7.0 mmol/l) at the time of diagnosis, or individuals with a physician diagnosis of DM and presently on antidiabetic medication. 26 Optimal control of DM was defined as a glycated haemoglobin HbA 1c level of < 6.5%. 27 DN was defined as the presence of a UACR of 30 mg/g with or without eGFR < 60 ml/ Fig. 1. Renal duplex ultrasonograph of the right mid-pole interlobar artery with elevated RI.