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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 15  |  Issue : 2  |  Page : 77-82

Microalbuminuria among participants with high-normal blood pressure attending a tertiary health institution in Nigeria


1 Department of Medicine, Bayero University/Murtala Muhammad Specialist Hospital, Kano, Nigeria
2 Department of Medicine, Bayero University/Aminu Kano Teaching Hospital, Kano, Nigeria
3 Department of Medicine, Jos University Teaching Hospital, Jos, Nigeria

Date of Web Publication3-Jul-2019

Correspondence Address:
Dr. Saidu Hadiza
Department of Medicine, Bayero University Kano/Murtala Muhammad Specialist Hospital, Kano
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njc.njc_18_17

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  Abstract 


Background: Participants with high-normal blood pressure (BP) (systolic BP [SBP] 130–139 mmHg and/or diastolic BP [DBP] 85–89 mmHg) have higher cardiovascular disease (CVD) risk factors compared with optimal BP (SBP <120 mmHg and/or DBP <80 mmHg).
In the present study, the prevalence of microalbuminuria, factors associated with it, and other CVD risk factors were assessed among participants with high-normal BP in comparison to controls.
Methods and Results: Out of 200 participants screened, 92 with high-normal BP (Group 1) and 97 with optimal BP (Group 2) who had no history of hypertension or diabetes mellitus were consecutively recruited after satisfying the inclusion criteria. Microalbuminuria was determined using Micral test strips using first-morning urine sample. The mean age of participants in Group 1 was 33.39 ± 5.17 years, while that for Group 2 was 27.01 ± 7.4 years (P ≤ 0.001). The prevalence of microalbuminuria was higher among participants in Group 1 than in participants in Group 2 (12.9% vs. 4.1%, P = 0.037). Participants in Group 1 were older, had higher mean SBP, DBP, body mass index (BMI), fasting plasma glucose, total cholesterol, low-density lipoprotein cholesterol, and triglycerides than those in Group 2. Pearson's correlation coefficient showed a significant association between BMI and microalbuminuria among all the study participants (r = 0.625, P ≤ 0.007), and the BMI explains 37.7% of the variability of urinary albumin excretion among participants (R2 = 0.377, P = 0.007).
Conclusion: Participants with high-normal BP had a higher prevalence of microalbuminuria and risk factors for CVD than those with optimal BP. The results suggest that participants' BMI is linked to urinary albumin excretion, and if proven in larger studies, the findings might be useful in the early prevention of CVD among individuals with high-normal BP.

Keywords: High-normal blood pressure, microalbuminuria, Nigeria


How to cite this article:
Hadiza S, Musa KK, Basil O. Microalbuminuria among participants with high-normal blood pressure attending a tertiary health institution in Nigeria. Nig J Cardiol 2018;15:77-82

How to cite this URL:
Hadiza S, Musa KK, Basil O. Microalbuminuria among participants with high-normal blood pressure attending a tertiary health institution in Nigeria. Nig J Cardiol [serial online] 2018 [cited 2019 Nov 20];15:77-82. Available from: http://www.nigjcardiol.org/text.asp?2018/15/2/77/262000




  Introduction Top


High-normal blood pressure (BP), defined as sustained systolic BP (SBP) between 130 and 139 mmHg and/or diastolic BP (DBP) between 85 and 89 mmHg, is found to be associated with increased risk of cardiovascular events including progression to hypertension.[1]

The relationship between BP and the risk of cardiovascular event is continuous, consistent, and independent of other risk factors.[1] The higher the BP, the greater is the chance of developing heart attack, heart failure, stroke, and chronic kidney disease.[1] SBP values in the range of 130–139 mmHg and DBP 85–89 mmHg are associated with more than two-fold increase in the relative risk of developing cardiovascular disease (CVD) in 10 years compared with normal BP.[2]

High-normal BP is associated more frequently than normal BP with other CVD risk factors including microalbuminuria.[2] It has been shown that microalbuminuria is a useful biomarker of individuals who are at risk for CV events and who require more intensive therapy.[3]

The relationship between high-normal BP and microalbuminuria has not been well described in Sub-Saharan Africans including Nigerians, as previous studies were mainly on Caucasians.[4],[5] Findings in Caucasians may be different from that of Non- Caucasians. In the present study, therefore, we compared the prevalence of microalbuminuria and other CVD risk factors between participants with high-normal BP and optimal BP in a Nigerian tertiary health institution.


  Methods Top


The study was cross-sectional and comparative, carried out at Aminu Kano Teaching Hospital, a tertiary health-care institution in Kano State, North-western Nigeria. The study protocol was approved by the Research Ethics Committee of the hospital, before the commencement of the study. The study conformed to the Declaration of Helsinki on investigations involving human participants.[6] The study was explained to the patients in English or in the local language (Hausa) and written informed consent obtained before enrollment into the study.

Study population

The study population comprised of patients at least 18 years of age, attending the general outpatient clinic of the hospital. There were two patient groups; those with high-normal BP (Group 1) and those with optimal BP (Group 2) and participants were matched for gender.

Out of 200 patients (100 patients for each group) consecutively selected, 186 patients who fulfilled the inclusion criteria were studied. Exclusion criteria included participants <18 years of age, those with overt proteinuria, and those on drugs known to increase BP such as steroids and contraceptive pills. Furthermore, participants previously or newly diagnosed with hypertension, diabetes mellitus (DM), renal disease, or renal insufficiency (serum creatinine >1.2–2 mg/dl [>105.6–176 umol/L]) were excluded from the study.

Measurement of blood pressure and microalbuminuria

BP was measured using mercury sphygmomanometer according to the recommendations of the American Society of Hypertension.[7] The patient was allowed to relax for 5 min before the first reading, and an average of 2 readings was taken 15 min apart. BP levels were defined using the World Health Organization-International Society of Hypertension (WHO-ISH) classification.[1] High-normal BP was defined as SBP of 130–139 mmHg and/or DBP 85–89 mmHg, whereas optimal BP was defined as SBP of <120 mmHg and/or DBP of <80 mmHg.[1]

The first voided morning urine sample was tested by the researcher for microalbuminuria using an immunochemical semi-quantitative kit (Micral Test™, Roche Diagnostics, USA, 2010.) which measures albumin in the range of 20–200 mg/L.[8] Microalbuminuria was defined as 20–200 mg/L albumin in urine.[9] Detection levels at ≥20 mg/L were considered positive.[7]

Measurement of other variables

CVD risk factors assessed in the present study included overweight/obesity, fasting plasma glucose (FPG), and dyslipidemia which were recognized in the 2003 WHO-ISH guidelines for the management of hypertension.[1]

Body mass index (BMI) was calculated from the weight in kilograms taken with minimal clothing using a standardized weighing scale and divided by the square of height in meters. Height was taken using stadiometer without shoes or headgear. The WHO defined overweight as BMI of 25.0–29.9 kg/m 2 and obesity as BMI of 30 kg/m 2 or more.[10]

Venous blood samples were collected after an overnight fast for 10–12 h. Samples for plasma lipids were placed in labeled plain universal bottles, while that for FPG was placed in fluoride oxalate bottles. They were analyzed in the hospital Chemical Pathology laboratory using the autoanalyzer machine (Chiron Diagnostic-Bayer, England, 2009).

Dyslipidemia was defined using the National Cholesterol Education Programme-Adult Treatment Panel III guidelines and was considered to be present if all or any of the following are found; total cholesterol (TC) ≥200 mg/dl (5.2 mmol/L), low-density lipoprotein cholesterol (LDL-C) ≥130 mg/dl (3.33 mmol/L), triglycerides (TG) ≥150 mg/dl (3.38 mmol/L), and high density lipoprotein cholesterol (HDL-C) ≤40 mg/dl (1.0 mmol/L) in men or if ≤50 mg/dl (1.2 mmol/L) in women.[11] DM was defined by the WHO criteria as FPG ≥126 mg/dl (7 mmol/L) and/or random plasma glucose ≥200 mg/dl (11.1 mmol/L) in the presence of typical symptoms of DM or on at least two occasions if there are no such symptoms.[12]

Statistical analysis

The statistical analysis was conducted using SPSS version 19 (Chicago, IL, USA). Continuous variables were presented as mean ± standard deviation. Qualitative variables were expressed as proportions and percentages. The Chi-squared or Fisher's exact tests were used to compare proportions, while Student's t-test was used to compare means. Pearson's correlation coefficient (r) was employed to examine linear associations. P < 0.05 was considered the minimum for statistical significance.


  Results Top


Out of the 200 patients screened, 186 were studied (92 in Group 1 and 97 in Group 2). Ten were excluded due to the presence of overt proteinuria (7 from Group 1 and 3 from Group 2), and an additional one from Group 1, due to the presence of DM. The mean age of participants in Group 1 was 33.39 ± 5.17 years, while that for Group 2 was 27.01 ± 7.4 years (P ≤ 0.001). Among participants in Group 1, 41 (44.5%) were males, while 51 (55.5%) were females, while among participants in Group 2, 43 (44.3%) were males and 54 (55.7%) were females (P = 0.96).

Participants with high-normal BP had a higher mean SBP, DBP, BMI, FPG, TC, LDL-C, and TG and lower levels of HDL-C when compared with those with normal BP [Table 1]. In addition, the prevalence of microalbuminuria in participants with high-normal BP was also higher than in those with normal BP (12.9% vs. 4.1%, P = 0.037) [Table 1].
Table 1: Comparison of clinical and laboratory findings of the study population

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Comparative analysis between micro-albuminuric and normoalbuminuric participants showed that microalbuminuric participants had higher SBP, DBP, FPG, TC, and BMI than normoalbuminuric participants [Table 2]. Pearson's correlation coefficient showed a significant positive correlation between BMI and microalbuminuria among all the study participants (r = 0.625, P ≤ 0.007), and the BMI explains 37.7% of the variability of urinary albumin excretion among participants (R2 = 0.377) as shown in [Figure 1]a. There was no significant correlation between both SBP and DBP with microalbuminuria [Figure 1]b and [Figure 1]c.
Table 2: Comparison of clinical and laboratory findings between normoalbuminuric and microalbuminuric participants

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Figure 1: (a) Relationship between body mass index and microalbuminuria among the study participants, r = 0.625, P = 0.007. (b) Relationship between systolic blood pressure and microalbuminuria among the study participants. (c) Relationship between diastolic blood pressure and microalbuminuria among the study participants

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  Discussion Top


In the present study, comparing prevalence of microalbuminuria and other CVD risk factors in participants with high-normal BP and those with optimal BP, participants with high-normal BP were found to have a higher prevalence of microalbuminuria and other CVD risk factors than participants with optimal BP. We also reported higher SBP, DBP, FPG, TC, and BMI in microalbuminuric than normoalbuminuric participants.

The finding of higher CV risk profiles including microalbuminuria, among participants with high-normal BP in this study, is consistent with what had been reported previously.[4],[5],[13],[14],[15],[16] Participants with high-normal BP were older and had a higher mean SBP, DBP, BMI, FBG, TC, TG, and LDL-C. We found lower mean HDL-C among participants with high-normal BP consistent with some studies.[5],[15] Other studies, however, reported higher mean HDL-C levels among participants with high-normal BP.[14],[16] Kim et al., in addition, reported higher levels of serum ferritin and fasting insulin levels among participants with high-normal BP. These were not assessed in this study due to unavailability of the laboratory facilities. They also reported significant positive association of microalbuminuria with high normal BP category, fasting insulin, TC, TG, and metabolic syndrome.[5] The higher prevalence of microalbuminuria in the high-normal BP participants with apparent normal renal function may reflect increased glomerular filtration pressure in response to elevated BP.[17] Knight et al. found SBP, DBP, and mean arterial pressure as independent predictors of microalbuminuria.[4] Although the present study did not assess for metabolic syndrome, it showed significant association between BMI and microalbuminuria among all the study population and the BMI explains 37.7% of the variability of urinary albumin excretion among participants. Independent predictors for microalbuminuria were not evaluated in this study due to the lower prevalence of microalbuminuria observed, the result of which may be attributed to the smaller sample size compared to other studies.[4],[5] A previous study in Beijing reported obesity as an independent risk factor for microalbuminuria, while other studies showed abdominal obesity rather than overall obesity as an independent risk factor for microalbuminuria.[18],[19],[20]

In the Framingham study, participants with high-normal BP had a markedly increased risk for developing sustained hypertension and are associated with more than two-fold increase in the relative risk of developing CVD in 10 years compared with optimal BP.[17] Microalbuminuria is a widely identified marker of vascular dysfunction, including endothelial dysfunction, and it is associated with other CVD risk factors [21] Its presence markedly increases the risk for cardiovascular morbidity and mortality among patients with diabetes, hypertension, and in the general population.[22],[23],[24],[25],[26] Urinary albumin excretion has been also reported as a predictor of developing hypertension and BP progression.[26] A study of 8751 nonhypertensive participants in the National Health and Nutrition Examination Survey III cohort found that high-normal BP categories were significantly associated with increased odd ratio (OR) of microalbuminuria, compared with optimal BP (OR = 2.13; 1.34, respectively).[27] Furthermore, a prospective study of 1499 nondiabetic, nonhypertensive individuals has demonstrated that those in the highest quartile of the urine albumin-creatinine ratio (UACR) had an adjusted OR of 1.93 for developing hypertension and 1.45 for BP progression.[28] These data suggest that subclinical abnormalities in the kidney or vascular endothelium might proceed to the development of higher BP.

Our findings imply the need for screening individuals with high-normal BP for other CVD risk factors including microalbuminuria. There is also need for additional studies to evaluate clinical outcome of more active treatment in individuals with high-normal BP, especially those with high-risk profiles. Current guidelines have recommended that participants with high-normal BP values should be managed with lifestyle measures.[29],[30] The Dietary Approach to Stop Hypertension dietary pattern, weight loss, reduced sodium intake, physical activity, and moderation of alcohol intake have been shown in clinical trials to prevent the development of hypertension. Individuals in the high-risk or very high-risk categories may also require prompt BP lowering through drug administration. They may also require nonhypertension-related intervention such as administration of antiplatelet drugs and statins.[30]

Study limitations

Our study has a number of limitations. Being a hospital-based study, with a small sample size, the findings may not be fully applicable to the general population. In addition, only one-morning urine sample was collected for the assessment of micro-albuminuria due to the cross-sectional nature of the study. Thus, false-positive results may have occurred. The amount of albumin excreted in urine may also vary with changes in posture, physical activity, amount of hydration, and fever among other factors giving false-positive result. Multiple samples may, therefore, provide more accurate results. The Micral strips used in this study are largely used for screening; hence, the results should ideally be confirmed using UACR.

In spite of all the challenges, the study is among the few in Sub-Saharan Africa to show that participants with high-normal BP had higher CVD risk and with a higher prevalence of microalbuminuria than those with optimal BP. We, therefore, recommend larger population-based longitudinal studies to determine the prevalence and determinants of microalbuminuria among participants with high-normal BP.


  Conclusion Top


Participants with high-normal BP have greater risk factors for CVD including microalbuminuria, than those with optimal BP. We, therefore, suggest all individuals with high-normal BP to be screened for other CVD risk factors and have them corrected through the initiation of lifestyle measures for early prevention of CVD. Moreover, microalbuminuria may be a surrogate marker for increased cardiovascular risk in individuals with high-normal BP. Further investigations are, therefore, needed to ascertain whether alteration in microalbuminuria in this BP category may prevent or delay development of hypertension and cardiovascular events.

Acknowledgment

We acknowledge Dr. Ahmad Yakasai Maifada for his assistance in data analysis and interpretation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Knight EL, Kramer HM, Curhan GC. High-normal blood pressure and microalbuminuria. Am J Kidney Dis 2003;41:588-95.  Back to cited text no. 4
    
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Kim BJ, Lee HJ, Sung KC, Kim BS, Kang JH, Lee MH, et al. Comparison of microalbuminuria in 2 blood pressure categories of prehypertensive subjects. Circ J 2007;71:1283-7.  Back to cited text no. 5
    
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Hillege HL, Janssen WM, Bak AA, Diercks GF, Grobbee DE, Crijns HJ, et al. Microalbuminuria is common, also in a nondiabetic, nonhypertensive population, and an independent indicator of cardiovascular risk factors and cardiovascular morbidity. J Intern Med 2001;249:519-26.  Back to cited text no. 24
    
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Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo JL Jr., et al. The seventh report of the joint national committee on prevention, detection, evaluation, and treatment of high blood pressure: The JNC 7 report. JAMA 2003;289:2560-72.  Back to cited text no. 29
    
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