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Archives of cardiovascular diseases
Volume 109, n° 10
pages 527-532 (octobre 2016)
Doi : 10.1016/j.acvd.2016.02.009
Received : 8 November 2015 ;  accepted : 5 February 2016
Prevalence and factors associated with hyperuricaemia in newly diagnosed and untreated hypertensives in a sub-Saharan African setting
Prévalence et facteurs associés à l’hyperuricémie chez les sujets hypertendus nouvellement diagnostiqués et naïfs de tout traitement antihypertenseur en Afrique sub-saharienne
 

Félicité Kamdem a, b, , Marie-Solange Doualla a, c, Fernando Kemta Lekpa a, d, Elvis Temfack a, Yvette Ngo Nouga a, Olivier Sontsa Donfack a, Anastase Dzudie a, Samuel Kingue c
a Internal Medicine Unit, Douala General Hospital, P. O. Box 4856, Douala, Cameroon 
b Faculty of Medicine and Pharmaceutical Sciences, University of Douala, Douala, Cameroon 
c Faculty of Medicine and Biomedical Sciences, University of Yaoundé I, Yaoundé, Cameroon 
d Faculty of Health Sciences, University of Buea, Buea, Cameroon 

Corresponding author at: Internal Medicine Unit, Douala General Hospital, P. O. Box 4856, Douala, Cameroon.
Summary
Background

Few studies have evaluated the link between hyperuricaemia and cardiovascular disease in sub-Saharan Africa.

Aims

To assess the prevalence of and factors associated with hyperuricaemia among newly diagnosed treatment-naïve hypertensive patients in sub-Saharan Africa.

Methods

We performed a community-based cross-sectional study from January to December 2012 in Douala, Cameroon (Central Africa). We enrolled newly diagnosed treatment-naïve hypertensive patients, and excluded those with gout or a history of gout. Serum uric acid concentrations were measured by enzymatic colourimetric methods, and hyperuricaemia was defined as a serum uric acid concentration>70IU/mL. Fasting blood sugar concentrations, serum creatinine concentrations and lipid profiles were also measured. Logistic regression was used to study factors associated with hyperuricaemia.

Results

We included 839 newly diagnosed treatment-naïve hypertensive patients (427 women and 412 men; mean age 51±11 years; mean serum uric acid concentration 60.5±16.5IU/L). The prevalence of hyperuricaemia was 31.8% (95% confidence interval [CI] 28.7–34.9) and did not differ by sex (132 women vs. 135 men; P =0.56). Multivariable logistic regression identified age>55 years (adjusted odds ratio [AOR] 1.65, 95% CI 1.12–2.29), family history of hypertension (AOR 1.65, 95% CI 1.01–2.67), waist circumference>102cm in men or>88cm in women (AOR 1.60, 95% CI 1.12–2.29), low-density lipoprotein cholesterol>1g/L (AOR 1.33, 95% CI 0.97–1.82) and triglycerides>1.5g/L (AOR 1.63, 95% CI 1.01–2.65) as independently associated with hyperuricaemia.

Conclusion

Hyperuricaemia is common among newly diagnosed treatment-naïve hypertensive patients in sub-Saharan Africa and is associated with some components of the metabolic syndrome.

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Résumé
Objectif

Évaluer la prévalence et les facteurs associés à l’hyperuricémie chez les patients hypertendus nouvellement diagnostiqués et naïfs de tout traitement antihypertenseur en Afrique sub-saharienne.

Méthodes

Nous avons réalisé une étude transversale de janvier à décembre 2012 en milieu communautaire à Douala, Cameroun. Nous avons inclus tout patient hypertendu nouvellement diagnostiqué et naïf de tout traitement antihypertenseur et exclus tous ceux qui avaient une histoire actuelle ou passée de la goutte et les hypertendus sous traitement. L’hyperuricémie était définie par un taux d’acide urique sérique supérieur à 70UI/mL. La glycémie à jeun, la créatinimémie et le profil lipidique ont également été mesurés. La régression logistique était utilisée pour étudier les facteurs associés à l’hyperuricémie.

Résultats

Nous avons inclus 839 patients (427 femmes et 412 hommes) nouvellement diagnostiqués hypertendus et naïfs de tout traitement antihypertenseur. L’âge moyen était de 51 (SD : 11) ans, et le taux moyen d’acide urique sérique était de 60,5 (SD : 16,5) UI/L. La prévalence de l’hyperuricémie était de 31,8 % [IC95 % : 28,7 %–34,9 %], et ne diffère pas selon le sexe (femmes, n =132 vs hommes, n =135 ; p =0,56). En régression logistique multivariée, l’âge>55ans (AOR : 1,65 [1,12–2,29]), le tour de taille>102 chez les hommes et 88 chez les femmes (AOR : 1,60 [1,12–2,29]), le cholestérol LDL>1g/L (AOR : 1,33 [0,97–1,82]), les antécédents familiaux d’hypertension (AOR : 1,65 [1,01–2,67]), et les triglycérides>1,5g/L (AOR : 1,63 [1,01–2,65]) étaient indépendamment associés à l’hyperuricémie.

Conclusion

L’hyperuricémie est fréquente chez les patients hypertendus nouvellement diagnostiqués et naïfs de tout traitement antihypertenseur en Afrique sub-saharienne.

The full text of this article is available in PDF format.

Keywords : Hypertension, Hyperuricaemia, Uric acid, Cardiovascular risk factors, Sub-Saharan Africa

Mots clés : Hypertension artérielle, Hyperuricémie, Acide urique, Facteurs de risque cardiovasculaires, Afrique sub-saharienne

Abbreviations : CI, HDL-C, LDL-C, OR, TC, TG


Background

Hypertension affects about 1 billion people in the world, 10–21% of whom live in sub-Saharan Africa [1]. The prevalence of hypertension in Cameroon was 24% in 2010 [2]. Many traditional risk factors associated with hypertension have been identified. However, while hyperuricaemia is known to be a global marker in cardiovascular disease [3], its role as an independent cardiovascular risk factor is controversial. Hyperuricaemia is generally known to be associated with components of the metabolic syndrome, such as diabetes, dyslipidaemia, obesity and hypertension [3, 4, 5, 6, 7, 8, 9]. For many years, hyperuricaemia has been associated with the risk of developing hypertension [4, 5, 6, 8, 9, 10]. It has been experimentally proven that hyperuricaemia evolving for at least 5 years can cause renal abnormalities, which may lead to hypertension and cardiovascular complications [10]. The prevalence of hyperuricaemia has been estimated at 25% in hypertensive patients naïve to antihypertensive therapy [10]; nevertheless, hyperuricaemia itself is still not considered to be a classic cardiovascular risk factor. Most data have come from developed countries, with few studies having evaluated the link between hyperuricaemia and cardiovascular disease in sub-Saharan Africa [11, 12, 13]; because of this, we aimed to describe the prevalence of and factors associated with hyperuricaemia among newly diagnosed hypertensive treatment-naive patients, in the city of Douala, Cameroon (sub-Saharan Africa).

Methods

We conducted a cross-sectional study in the city of Douala, the economic capital of Cameroon (Central Africa), from January to December 2012. This study was performed in accordance with the ethical principles of the Declaration of Helsinki and was approved by the ethics committee of our hospital.

We enrolled all newly diagnosed consecutive hypertensive patients without antihypertensive drug intake from four healthcare centres. Patients with a history of gout or current gout were not included. A standardized case-report form was used for data collection, including sociodemographic, clinical and biological data. Blood pressure was measured after a 5-minute rest – 15minutes for those with elevated values – in a seated position using a calibrated aneroid manometer, and the diagnosis of hypertension was established after three consecutive measurements. Hypertension was defined as systolic blood pressure>140mmHg and/or diastolic blood pressure>90mmHg [14]. Treatment-naïve patients were defined as those who had never received any antihypertensive drug. Blood samples were collected after an 8-hour overnight fast, and were sent to the biochemistry laboratory at Douala General Hospital for analysis. Plasma creatinine, fasting blood sugar, total cholesterol (TC), triglycerides (TG) and high-density lipoprotein cholesterol (HDL-C) were measured using enzymatic colourimetric methods; low-density lipoprotein cholesterol (LDL-C) was calculated using the Friedewald formula (LDL-C=TCHDL-CTG/5, if TG<4g/L).

Operational definitions

Hyperuricaemia was defined as blood uric acid concentration>70mg/L [15]. Diabetes was defined as fasting blood sugar concentration>1.26g/L and/or antidiabetic drug intake [16]. The lipid profile was classified using the National Cholesterol Education Program in Adult Treatment Panel III (NCEP ATPIII) cut-offs as follows: TC<2g/L; LDL-C<1g/L; HDL-C>0.40g/L; and TG<1.5g/L [17].

Statistical analysis

We used STATA 12.0 for Windows (STATA Corp., College Station, TX, USA) for the data analysis. Quantitative variables are presented as means±standard deviations; qualitative variables are presented as absolute numbers and percentages. Statistical comparisons were made with Student's t -test for continuous variables and the Chi2 test for categorical variables. Factors associated with hyperuricaemia were analysed by univariate logistic regression, reporting odds ratios (ORs) and their 95% confidence intervals (CIs). All significant variables were mutually adjusted for each other in a final multivariable logistic regression model, after dropping one variable in a pair of highly correlated factors (to account for collinearity). A P -value<0.05 was used to indicate statistically significant results.

Results

During the study period, 839 patients (427 women and 412 men) were diagnosed with hypertension and were naïve to antihypertensive drug treatment. Among them, 76 were known hypertensive patients who were only on lifestyle changes (salt restriction in all cases). The baseline characteristics of the study population are summarized in Table 1; data are shown with a sex stratification.

Hyperuricaemia was found in 267 patients (31.8%), and did not differ significantly according to sex (132 women vs. 135 men; P =0.56). Table 2 shows the factors associated with hyperuricaemia, after univariate and multivariable analysis. In the univariate analysis, the likelihood of having hyperuricaemia was associated with the following factors: age>55 years (OR 1.6, 95% CI 1.18–2.18), family history of hypertension (OR 1.84, 95% CI 1.14–2.98), large waist circumference (OR 1.58, 95% CI 1.17–2.15), obesity (OR 1.32, 95% CI 0.99–1.77), elevated TC (OR 1.54, 95% CI 1.14–2.07), elevated LDL-C (OR 1.39, 95% CI 1.03–1.89) and elevated TG (OR 1.87, 95% CI 1.17–2.99). In the multivariable analysis, after adjustment for confounding factors, age>55 years (AOR 1.65, 95% CI 1.12–2.29), family history of hypertension (AOR 1.65, 95% CI 1.01–2.67), large waist circumference (AOR 1.60, 95% CI 1.12–2.29), elevated LDL-C (AOR 1.33, 95% CI 0.97–1.82) and elevated TG (AOR 1.63, 95% CI 1.01–2.65) increased the likelihood of having hyperuricaemia.

Discussion

The aim of this study was to describe the prevalence of and factors associated with hyperuricaemia among newly diagnosed hypertensive patients who were naive to antihypertensive drugs, in Cameroon. Previous studies from developed countries had shown that approximately 25% of patients with essential hypertension had hyperuricaemia [10]. Also, hyperuricaemia was found to be associated with an increased risk of incident hypertension, independent of the traditional risk factors for hypertension [4]. The main finding of our study is that hyperuricaemia was common in a sub-Saharan African population with hypertension who were naïve to antihypertensive drug treatment; indeed, one-third of our study population had hyperuricaemia. To the best of our knowledge, this study is the first to report on the high prevalence of hyperuricaemia in this group of patients. Our findings are similar to those seen in developed countries, with a higher risk among African Americans compared with Caucasians [8, 18]. Our data add to previously published data highlighting the role of hyperuricaemia as a risk factor for hypertension (and probably for metabolic syndrome) [4, 5, 7]. As shown in our study and in others, hyperuricaemia exists before the onset of hypertension. The frequency of hyperuricaemia is multiplied by 2 after initiation of antihypertensive treatment, and hyperuricaemia may be present in all hypertensive patients with malignant hypertension, kidney disease or other cardiovascular complications [10]. Furthermore, we showed in our study that hyperuricaemia is more common in untreated hypertensive patients than classic risk factors, such as lipid profile abnormalities, kidney dysfunction and diabetes. Thus, as suggested by Kuwabara et al. [6], early detection of hyperuricaemia could certainly change the therapeutic approach to the hypertensive patient, considering not only blood pressure values, but all components of the metabolic syndrome and the serum uric acid concentration.

The second aim of our study was to identify the factors associated with hyperuricaemia in this sub-Saharan African population. We found that age, family history of hypertension, large waist circumference and lipid profile abnormalities (particularly elevated LDL-C and TG) were more common in those with hyperuricaemia; surprisingly, diabetes, fasting glucose and HDL-C were not associated with this risk. Further investigations are needed to confirm these findings.

Our study was limited by its cross-sectional nature, which gives just a point estimate of hyperuricaemia among these patients, and cannot be used to draw conclusions about the dynamics of hyperuricaemia in this population. In addition, one cannot be very confident about the associated factors, because of the limited number investigated; however, the large sample size of our study reduces the effect of this limitation. The description of Cameroon as “Africa in miniature”, with its central location on the continent, the diversity of its climate and the melting pot of its population, with characteristics found in several ethnic groups in sub-Saharan Africa, calls for the generalization of our results to all sub-Saharan Africa. However, further studies are needed to monitor the kinetics of serum uric acid concentrations and factors associated with hyperuricaemia in these patients, and to develop “tropicalized” management strategies.

Conclusions

In conclusion, hyperuricaemia is found in about one in three newly diagnosed untreated hypertensive patients in Cameroon. In these patients, hyperuricaemia is associated with some components of the metabolic syndrome.

Sources of funding

None.

Disclosure of interest

The authors declare that they have no competing interest.

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