Study design and site
This was a hospital-based cross-sectional study with consecutive sampling technique,
conducted amongst SCD patients attending the sickle cell clinic at the Tema General
Hospital (TGH), Tema, Ghana. The study was conducted from December 2013 to May 2014.
TGH serves as the main referral centre for residents of the south-eastern parts of
Ghana and offers general and specialist care services.
Study population
One hundred and ninety- four participants were recruited for the study. A structured
questionnaire (Additional file 1) was administered to each participant via interview, to obtain information on demography
and clinical history (confirmed and reviewed via patient charts). To be eligible,
participants had to be aged 5Â years and above with confirmed HbSS or HbSC and in a
steady clinical state for at least two weeks before recruitment. Individuals with
sickle cell trait (HbAS) were not included in the study. Participants with symptoms
suggestive of sickle cell pain crisis, acute illness (including having a fever or
needing referral to an urgent care centre), clinically suspected urinary tract infection
and gross haematuria were excluded. We excluded participants who were known to be
infected with HIV or with a systemic condition that could result in a glomerulopathy
not related to SCA (e.g. active hepatitis B or C infections, systemic lupus erythematosus).
Ethical consideration
The study was approved by the Institutional Review Board, University of Cape Coast
(IRB/UCC) and the Committee of Ethics, Tema General Hospital. Participation was voluntary
and written informed consent was obtained from participants or from parents and guardians
of children. Data was de-identified before analysis.
Blood pressure measurement
Trained personnel measured the blood pressure of participants (mercury sphygmomanometer
and stethoscope) in accordance with recommendations of the American Heart Association
15]. Repeated measurements were taken within 5–10 minutes rest interval and the mean
value was recorded as the blood pressure.
Anthropometry
Height (to the nearest 0.1Â cm) without shoes was measured with a wall-mounted ruler
(LINDELS, Klippan, Sweden). Weight (to the nearest 0.1Â kg) in light clothing was measured
with a balance (Seca, Hamburg, Deutschland). Body Mass Index (BMI) was calculated
using the formula; weight (kg)/height (m2). Overall obesity was defined as a BMI of ?30 kg/m2, normal weight as 18.5–24.9 kg/m2, underweight as 18.5 kg/m2 and overweight as 25.0–29.9 kg/m2 in adults 16]. In children however, we defined according to the CDC, ?95th percentile as obese,
85th-94th percentiles as overweight and 5th-84th percentile as normal and 5th percentile as underweight 17],18].
Blood sample collection and processing
Five millilitres of venous blood was obtained from each participant into serum gel
separator (SST) and Ethylenediaminetetraacetic acid (EDTA) anticoagulated tubes, from
which biochemical and haematological assays were performed respectively. Haematological
assays were performed on fresh anticoagulated blood using an automated analyser (Mindray
BC 3000 Plus, Shenzhen, China). Blood in SST’s were allowed to clot, centrifuged at
1500Â g for 3Â minutes, and serum creatinine was estimated using an automated chemistry
analyser (Selectra Junior, Vital Scientific NV, Netherlands).
Urine sample collection and processing
Participants provided early morning urine, collected into a clean, dry, sterile and
wide-necked container. Urine protein was estimated semi-quantitatively using commercially
available urine test strips (highly sensitive for albumin) as per manufacturer’s instructions.
“Trace†protein is equivalent to 10 mg/100 ml or about 150 mg/24 hours (the upper
limit of normal). 1+ corresponds to about 200–500 mg/24 hours; 2+ to 0.5-1.5 g/24 hours,
a 3+ to 2–5 g/24 hours, and a 4+ represents 7 g/24 hours or greater.
Outcome criteria
The estimated GFR (eGFR) was calculated for adults using the chronic kidney disease
epidemiology collaboration (CKD-EPI) equation 19] and the Schwartz equation was used for children (?17Â years) 20], 21]. The CKD-EPI equation for creatinine used was as follows:
where Scr is serum creatinine in mg/dl, k is 0.7 for females and 0.9 for males, ? is ?0.329 for females and ?0.411 for males,
min indicates the minimum of Scr /? or 1, and max indicates the maximum of Scr /? or 1.
The CKD-EPI equation has recently been suggested as the best option for the eGFR determination
in SCD 22].
The updated Schwartz equation used was as follows:
The calculated eGFR was used to stratify the study population into stages of CKD,
based on the staging system of the Kidney Disease: Improving Global Outcomes (KDIGO)
guidelines for CKD. The various stages were defined as follows: Stage 1 (Kidney damage
with normal or increased eGFR)?=??90 ml/min/1.73 m2; Stage 2 (Kidney damage with mildly decreased eGFR)?=?60–89 ml/min/1.73 m2; Stage 3a (mild to moderately decreased eGFR)?=?45–59 ml/min/1.73 m2; Stage 3b (moderate to severely decreased eGFR)?=?30–44 ml/min/1.73 m2; Stage 4 (severely decreased eGFR)?=?15–29 ml/min/1.73 m2 and Stage 5 (Kidney failure)?=?15 ml/min/1.73 m219]. CKD according to KDIGO organization is defined as either decreased estimated glomerular
filtration rate (eGFR??60 mL/min/1.73 m2 corresponding to stage 3–5) or evidence of kidney damage (albuminuria, or overt proteinuria
23]. Glomerular hyperfiltration was defined as eGFR 140 24], 25].
Statistical Analysis
Values are expressed as mean?±?SD or frequencies and proportions. Differences between
groups were determined by unpaired t test, Chi-square, Fisher’s exact test or ANOVA, where appropriate. A multivariate
logistic regression was performed to determine the factors, which may be associated
with CKD amongst different populations. P 0.05 was considered statistically significant. Analysis was performed using GraphPad
prism version 5.0 (GraphPad software, San Diego California USA).