CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 3, July/August 2023 158 AFRICA Participants with missing data relating to kidney function were excluded from the analysis. Blood pressure was measured using an Omron M6 (HEM-7321-E) automated machine (Kyoto, Japan). This device has been validated according to the European Society of Hypertension International Protocol in a European population.7 Blood pressure was measured by trained research assistants and inter-observer variability was determined by checking for reproducibility and repeatability between all research assistants prior to commencement of the study. Participants had to have refrained from smoking or doing any physical exercise for 30 minutes prior to the measurement. They were asked to sit comfortably with legs uncrossed and backs supported for five minutes before readings were taken. Three measurements were taken on the left arm at two-minute intervals using an appropriately sized cuff determined by the mid-upper arm circumference of the participant. The average of the three recordings was recorded for analysis. If there was a difference of > 5 mmHg between any of the three measurements, a fourth measurement was taken and the average of the lowest three measurements was recorded for analysis. Participants were grouped into one of three categories, as defined by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, the JNC7 report. Normotensive was defined as systolic blood pressure (SBP) < 120 mmHg and diastolic blood pressure (DBP) < 80 mmHg; prehypertensive: SBP ≥ 120 mmHg and <140 mmHg or DBP ≥ 80 mmHg and < 90 mmHg; or hypertensive: SBP ≥ 140 mmHg or DBP ≥ 90 mmHg. This classification is supported by the JNC7 report to better identify those at risk for developing hypertension.8 Participants in the prehypertensive or hypertensive categories were classified for analysis as having EBP. Trained research assistants carried out anthropometric measurements. These research assistants underwent assessment prior to the study and the co-efficient of variation was < 2%. Weight was measured on a digital scale to the nearest 0.1 kg and standing height to the nearest 0.1 cm with a wall-mounted stadiometer (Holtain, United Kingdom). Waist circumference was measured with a tape measure at the midpoint between the iliac crest and the lowest palpable rib in the mid-axillary plane to the nearest 0.1 cm. Hip circumference was measured at the most protruding part of the buttocks with the participant standing. The average of three measurements was recorded. Waist:hip ratios and body mass indices (BMI) [weight (kg) divided by height squared (m2)] were derived from these data. A standardised questionnaire was administered by trained research assistants. Participants answered questions with regard to past and current risk factors relating to hypertension and kidney disease. These included questions relating to any family history of hypertension, diabetes, hypercholesterolaemia, heart disease and/or renal disease, any history of being diagnosed with any of the above, any history of childhood or adult urinary tract infections, kidney stones or dialysis (acute or chronic) and questions relating to smoking and alcohol habits, over-thecounter and illegal drugs, traditional medicines and use of snuff. Women were asked about their number of pregnancies and live births, contraceptive use and gestational hypertension. Socio-economic status (SES) was measured using an asset-based household SES measured tool based on a validated standardised questionnaire by the Demographic and Health Survey for Developing Countries (available at http://www.dhsprogram.com/). Fasting blood samples were obtained in serum separator tubes for measurement of serum creatinine and uric acid levels. Blood tubes were allowed to stand for 30 to 60 minutes before being centrifuged at 3 000 rpm for 10 minutes and serum was decanted and frozen at –80ºC. Serum creatinine level was measured by the Jaffe method that was IDMS-traceable to a standard reference material, using a Cobas 6000/c501 analyser. The laboratory adheres to standard daily internal quality-control procedures, and a strict external quality-control programme through the College of American Physicians with approved certification for urine and serum chemistry for the time period in which testing was performed. Estimated glomerular filtration rate (eGFR) was then calculated using the CKD-EPI(creatine) 2009 equation not corrected for African-American ethnicity. Uric acid level was measured by enzymatic colorimetric testing on the Roche/Hitachi Cobas c analyser. Mid-stream urine samples were collected after clear instructions to participants to ensure minimal contamination of specimens. Women had to be at least two days post menses for urine to be collected. Urine dipstick testing was performed by trained research assistants using the Roche Combur® 10 sticks, which were calibrated weekly. Urine dipstick results for haematuria, leukocyturia and proteinuria were recorded as per dipstick result. Any degree of positivity for blood or protein was then analysed as positive. Urine pregnancy tests were performed on all female participants using an antibody-based urine HCG strip test. Specimens were then stored in ice for a maximum of two hours before being centrifuged at 1 600 rpm for 10 minutes and stored at –80ºC. Urine albumin concentration was measured using a colorimetric method on the Cobas 6000/c501 analyser and urine creatinine by the Jaffe method on the same analyser. The urine albumin:creatinine ratio (uACR) was calculated and used to classify albuminuria as normal (uACR < 3 mg/mmol); microalbuminuria (3–30 mg/mmol); and overt albuminuria (uACR > 30 mg/mmol). Participants with microalbuminuria and overt albuminuria were grouped together due to small numbers in the overt albuminuria group. Finger-prick testing for HIV using an antibody ELISA-based test kit was performed by nurses or research assistants who had completed a certified course in HIV counselling and testing. All participants signed consent for testing and received pre- and post-test HIV counselling. Participants who had positive test results were referred to their local HIV clinic for confirmatory testing and the initiation of anti-retroviral therapy. Statistical analysis All statistical analyses were done using STATA 15.0. For categorical variables and continuous variables with normal distribution, t-tests, chi-squared tests and ANOVAs were done to compare study characteristics by gender and hypertension risk. Mann–Whitney and Kruskall–Wallis tests were done to compare variables that were not normally distributed. Multiple linear regression models were run to assess the associations between SBP and DBP with contemporary growth factors, risk factors and measures of renal function. Participants with missing data related to kidney function such as serum creatinine or uACR
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