Introduction

Diabetes mellitus is a metabolic disease characterised by hyperglycaemia due to defects in insulin secretion, insulin action, or both. It affects approximately 422 million people worldwide, the majority of whom live in low and middle-income countries, and is directly responsible for 1.6 million deaths each year. In recent decades, the number of cases and the prevalence of diabetes have been steadily increasing [1]. Africa has the lowest prevalence of diabetes (4.2%) compared to other continents, but the prevalence and burden of the disease is increasing rapidly in Africa [2]. The prevalence of diabetes in Cameroon was estimated to be around 6% in 2018 [3]. The chronic hyperglycaemia associated with this condition causes a lot of damages and long term defects, leading to the development of other non-communicable diseases and micro/macro-vascular changes in various organs, of which the kidney is one of them [4]. Diabetes is the leading cause of end-stage renal disease (ESRD) worldwide, with approximately 40-60% of people with type 2 diabetes developing diabetic nephropathy (DN) after 10-15 years of diabetes progression [5,6]. In addition, diabetic complications are more common in underdeveloped countries due to lack of screening tools, early diagnosis and access to health care, resulting in a rapid onset of problems associated with this disease [6,7]. Diabetic nephropathy is one of the major complications of diabetes; however, data on this important connectedness are limited in sub-Saharan Africa (SSA). Effective management of diabetes and early diagnosis of diabetic nephropathy can delay progression to chronic kidney disease [5]. A study by Adebamowo and collaborators in 2016 on the impact of type 2 diabetes on renal function impairment in sub-Saharan African populations showed that type 2 diabetes was associated with a 50% increased risk of renal function impairment in this sample of sub-Saharan African adults [8]. In Ethiopia, a study conducted by Taderegew in 2020 on the assessment of renal failure using estimated glomerular filtration rate in patients with type 2 diabetes showed that renal failure was prevalent in patients with type 2 diabetes. Older age, female sex, duration of diabetes, hypertension, poor glycaemic control and BMI (body mass index) were significantly associated with renal failure [6]. Several authors have worked on diabetes in Cameroon, but few studies have focused on diabetic nephropathy, however, a study that aimed to determine the prevalence and biomarkers of diabetic nephropathy (DKD) in diabetic patients undergoing treatment in Buea and Ngaoundéré in Cameroon found a significant association between diabetic nephropathy and two variables: female sex and hypercreatinemia [9]. Because of the high prevalence of diabetes and kidney disease in Cameroon, it was necessary to conduct this research to compare glomerular filtration rate in medically monitored diabetic patients, those not monitored and healthy individuals.

Methods

This case-control study; took place from June to August 2015 at the Cité Verte District Hospital. A total of 99 patients were recruited between 8am and 12pm from Monday to Friday into the study. The latter was approved by the Faculty of Sciences (Department of Biomedical Sciences) of the University of Ngaoundéré, permitting our team to go the field; and by the Director of Cité Verte District Hospital, permitting us to start the survey. In addition, all participants in the survey signed an informed consent form after a brief presentation of the study's objective and benefits. The study included all known diabetic patients not taking any treatment and not under the care of a physician, who were considered cases, and diabetic patients under treatment and regularly followed up at the Cité Verte District Hospital; as well as healthy people (non-diabetic and without any pathology affecting renal function) who were considered controls. Patients had to be between 20 and 65 years of age and that must have signed the consent form. Patients over 65 years of age were not included because with age there is a decrease in glomerular filtration rate. Of the total of 99 patients recruited, 36 were diabetic patients under treatment, 32 diabetic patients not taking any treatment (naive), and 31 healthy patients suffering neither from diabetes nor from pathologies that could influence renal function. The data collection form (questionnaire) was used to identify patients meeting the inclusion criteria and was completed by each study participant under the supervision of the investigator. The questionnaire contained information on socio-demographic characteristics (sex, age, place of residence and occupation of the participants) and duration of the disease. After completing the questionnaire, blood pressure was measured with an electric blood pressure monitor on the participant's left arm in a sitting position after at least 10 minutes of rest, followed by blood and urine sampling. A volume of 5 ml of venous blood was collected after one night of fasting (8-10h) from all participants. These samples were sent to the laboratory, centrifuged and the serum was used to determine serum urea and creatinine. The determination of blood urea was carried out using the BIOLABO kit, by the enzymatic and colorimetric method based on the specific action of urease which hydrolyses urea into carbonate and ammonium ions. The ammonium ions then form a blue-green coloured complex with the chlorine salicylate. The intensity of the colouration is proportional to the concentration of urea in the sample and is measured at 600 nm [10]. The determination of serum creatinine was carried out using the kinetic two-point colorimetric method based on the Jaffé reaction. The method consists of measuring the intensity of the colouration of the red-orange complex formed by creatinine and picric acid in alkaline medium at 510 nm; the rate of colour formation is proportional to the concentration of creatinine in the sample [11]. These two parameters were used to explore renal function.

20-30 ml of urine sample was collected after blood collection by each participant in a dry, sterile jar. They were asked to collect the urine in the middle of the stream. Qualitative and semi-quantitative analyses of glycosuria and proteinuria on urine reagent strips were performed. Glomerular filtration rate (GFR) is the volume of plasma filtered by the kidneys per unit time. This was estimated using the Modification of Diet in Renal Disease (MDRD) formula as follows: GFR =186×SCr (mg/dl)-1.154 × age (years)-0.203 × 0.742 (if female) × 1.210 (as our population was African), (SCr is serum creatinine) (12). We calculated it automatically from the eGFR calculator software. Normal glomerular filtration rate is between 90-120 ml/min/1.73m² and a GFR < 60 ml/min/1.73m² is considered pathological according to the National Foundation of Kidney Disease.

Data processing and analysis

Data were entered using Epi-info software and, after verification, exported to SPSS (IBM SPSS Statistics for Macintosh, Version 20.0. Armonk, NY) for analysis. Quantitative data were expressed as mean and standard deviation (X ± SD) and categorical variables were presented as frequency (N) and percentage (%). The chi-square test was used to compare biochemical and clinical parameters of diabetic patients according to the duration of the disease; and the ANOVA test was used to determine the differences between the means of the different subgroups. The bivariate logistic regression model was used to determine the independent risk factors for GFR impairment in diabetic patients. The degree of association was expressed using the odds ratio (OR) and 95% CI. P value of less than 0.05 was considered statistically significant.

Results

Table 1 shows that of the 99 participants recruited, 36 (36.4%) diabetics under treatment, 32 (32.3%) were treatment-naive diabetics while 31 (31.3%) were healthy individuals. Our population was predominantly female that is 69.7% female versus 30.3% male, 53, 5% of participants were ≤ 50 years old and 46.5% were > 50 years old. According to marital status, married participants were the most represented (54.5%), while 82.8% of participants lived in urban areas and only 17.2% lived in rural areas. Table 2 shows that the mean age is almost similar in diabetic patients (treatment and naive) while healthy patients were younger (30 ± 11.89). The difference in age was significant. Regarding the biochemical parameters, the mean uremia and creatinemia were higher in the diabetic naive patients (1.15 ± 4.17g/l and 13.22 ± 6.75mg/l respectively) compared to the other two groups, healthy and treatment patients. The difference was statically significant (p<0.05). No significant difference was observed for proteinuria and glucosuria in the different groups. The mean glomerular filtration rate was significantly lower in naive diabetic patients (65.88 ± 23.19 ml/min/1.73m²) than in the other two groups in where the mean GFR was 86.50 ± 20.63 ml/min/1.73m2 for diabetic patients on treatment and 103.19 ± 22.9 ml/min/1.73m² for healthy patients, respectively. Table 3 presents the biochemical and clinical characteristics of diabetic patients according to the duration of the disease. It is noted that all naive patients had a disease duration of <10 years while 69.4% of the patients on treatment had a disease duration of ≥10 years. Patients with disease duration ≥ 10 years were less proned to albuminuria, glycosuria, hyper uremia and hyper creatinemia. They equally had a good estimate of glomerular filtration rate compared to those with < 10 years duration. The difference is significant (P < 0.05). There is an increase in systolic and diastolic blood pressure of 84% and 40%, respectively for patients with disease duration ≥ 10 years,. The difference was significant for systolic blood pressure. Table 4 shows that in diabetic patients, age group of > 50 years (OR=1.53; 95% CI: 0.43-5.49); no treatment (OR=27.2; 95% CI: 3.31-223.84); hyper-creatinemia (OR=26.40; 95% CI: 6.07-114.7); hyper-uremia (OR=8.16; 95% CI: 1.91-34.85); were independent risk factors for impaired glomerular filtration rate.

Table 1: Socio-demographic characteristics of the study participants

Table 2: Comparison of biochemical parameters in relation to glomerular filtration rate in the different participant subgroups

Low DFG <60 ml/ min/1.73m²

Table 3: Clinical and biochemical characteristics of diabetic patients according to the age of the disease.

*GFR: Glomerular Filtration Rate; OR: Odd Ratio; CI: Confidence Interval

Table 4: Independent risk factors for GFR impairment in patients with diabetes.

Discussion

The study was aimed at comparing glomerular filtration rate in medically monitored diabetic patients, to those who were medically monitored and non-diabetics. Diabetic nephropathy is a major cause of chronic failure worldwide, so assessment of renal function is important in diabetics [13]. Urea and creatinine are useful prognostic markers and predictors of kidney damage in diabetic patients. The results of this study show that for renal function parameters, urea and creatinine are normal in the healthy group and in the subgroup of diabetic patients on treatment and high in diabetic naïve patients, the difference being statistically significant (p<0.05) (table 2). These results are in agreement with those of Amartey et al. who obtained mean values of 87.09±41.91 µmol/l (9.9±4.76 mg/l) for creatinemia and 4.40±2.05 mmol/l (0.17±0.08 g/l) for uremia in a diabetic population followed up at the clinical laboratory in Ghana. These hypercreatinemia and hyperuremia observed in naive diabetic patients showed that the renal excretion rate of urea and creatinine is low in these patients. It is known that 90% of urea is excreted by the kidneys and 10% by the intestinal tract and skin, while creatinine is completely excreted by the kidneys. An increase in the blood level of both parameters is a sign of renal failure [14]. Glycosuria and albuminuria are also parameters for the exploration of renal function; these parameters indicate the presence of detectable glucose and albumin in the urine. Physiologically, glucose is exclusively reabsorbed by the proximal tubule through appropriate transporters, glycosuria occurs when the threshold of renal reabsorption is exceeded (1.80 g/l). The same is true for albumin which is totally reabsorbed at the glomerular capillary wall [15,16]. In our study, these two parameters were not statically significant. Treated and naive diabetic patients had almost the same percentages (table 2). A study by Wiwanikit in 2007 showed that prolonged glucosuria, subsequently leads to glomerular damage with reduced pore size and finally to albuminuria which is a late complication. Estimation of glomerular filtration rate (eGFR) is the best indicator for measuring the level of renal function and determining the stage of renal disease.  It is essential in diabetic patients, as diabetes is a known risk factor for kidney disease [17]. In our study, eGFR was assessed in type 2 diabetic patients and healthy patients using the MDRD equation.  In this study, the mean glomerular filtration rate in the different subgroups was above 60 ml/min/1.73m² ; although in the naive patients there was a more pronounced decrease in GFR. According to the National Kidney Foundation (2015), a GFR below 60 for three months or more or a GFR above 60 with kidney damage (marked by high levels of albumin in the urine) indicates chronic kidney disease and GFR between 89-60 ml/min/1.73m2 explains a mild loss of renal function. Uncontrolled diabetes has serious consequences for health and well-being, hence the importance of medical follow-up. Our study showed that all diabetic patients not followed up, had a disease duration of <10 years, and all patients with disease duration of ≥ 10 years were followed up and had better biochemical parameters. This shows that regular follow-up is essential to prevent complications and their aggravation. The objective of treatment and dietary follow-up is to maintain an optimal glycaemic balance hence the importance of medical follow-up. Indeed, poor glycaemic control in diabetic patients leads to the development and progression of diabetic nephropathy, which will result in the deregulation of various biochemical pathways with an increase in reactive oxygen species, activation of protein kinase C, and increased production of advanced glycation end products [18]. Hypertension is usually associated with diabetes, and its prevalence depends on disease duration, age, sex, history of glycaemic control and the presence of renal disease, among other factors [19]. The systolic blood pressure of our patients were significantly higher in those with disease duration of ≥ 10 years, this is in agreement with several studies that have shown that increased duration of type 2 diabetes is associated with an increased prevalence of hypertension [4,20,21]. Diabetic nephropathy is a type of kidney disease caused by diabetes. It has been shown that diabetic patients with common risk factors such as hypertension, poor glycaemic control, smoking, obesity and hyperlipidaemia are more likely to develop diabetic complications [22]. For this study, the independent risk factors for impaired glomerular filtration rate were age > 50 years, lack of medical follow-up, hypercreatinemia and hyperuremia. The loss of renal function as a result of aging has been known for decades, with most studies showing that advanced age is an independent predictor of impaired glomerular filtration rate [8,23]. It is hypothesised that the increase in cellular oxidative stress associated with ageing leads to endothelial cell dysfunction and changes in vasoactive mediators, resulting in increased atherosclerosis, hypertension and glomerulosclerosis [24]. With regard to hypercreatinemia, our results are consistent with a study conducted in a Cameroonian population by Ibrahim et al. who also found that hypercreatinemia was a risk factor for decreased renal filtration rate [9]. These results suggest that diabetes may be linked to chronic kidney disease (CKD) even in the absence of proteinuria.

Conclusion

In conclusion, our study showed that diabetic patients not under medical supervision were subject to a more rapid loss of kidney function than diabetic patients treated and supervised by health professionals. Prevention, early and adequate management are solutions to avoid the occurrence of complications in people with diabetes. This study remains preliminary and superficial, and therefore recommends further in-depth studies. Another study with improved sample size and dietary habits taken into account is also recommended.

List of abbreviations

DN : Diabetic Nephropathy

CKD: Chronic Kidney Disease

ESRD : End-Stage Renal Disease

eGFR: estimated Glomerular filtration rate

GFR: Glomerular filtration rate

MRDR : Modification of Diet in Renal Disease

SSA : Sub-Saharan Africa

SPSS: Statistical Package for the Social Sciences

Acknowledgements

The authors appreciate the cooperation of the patients in this study.

Funding

This research did not receive any specific funding from a public or non-profit funding body.

Availability of data and materials

The data and the study’s material are available to all from the authors upon request.

Authors’contributions

CSMB was involved in designing the project, wrote and revised the article draft, and analyzed the data; HTD assisted with data analysis and revised the article, AANA participated in the design of the project and read the article, RHH read and reviewed the article, CET participated in the data collection, SSB participated in the data collection, CT supervised the work. All authors read and approved the final manuscript.

Competing interest

The authors declare that they have no competing interests

Ethics approval and consent to participate

The protocol for this study was approved by the Faculty of Sciences of the University of Ngaoundéré and a research certificate was issued (N°2015/042/UN/DFS/CD-SBM), the study was also approved by the Director of the District Hospital of CITE VERTE who issued us a research authorization (N °0000186/MINSANTE/DRC/DSCV/HDCV). Written informed consent was obtained from all of the participants prior to participation in the study.

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