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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 1  |  Issue : 1  |  Page : 26-30

Distribution of plasma C-reactive protein measured by high-sensitivity assay in healthy Nigerian adults


Department of Chemical Pathology and Immunology, Aminu Kano Teaching Hospital, Kano, Nigeria

Date of Submission04-Aug-2013
Date of Acceptance16-Dec-2013
Date of Web Publication24-Mar-2014

Correspondence Address:
Isah Adagiri Yahaya
Department of Chemical Pathology and Immunology, Aminu Kano Teaching Hospital, Kano
Nigeria
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  Abstract 

Background: The plasma levels of C-reactive protein (CRP) within the reference interval have been shown to be a strong predictor of coronary heart disease (CHD) and are being considered in cardiovascular disease risk assessment. And for effective utilization of CRP in this regard, its distribution among healthy individuals in the general population should be established, using the high-sensitivity CRP (hsCRP). Aim: The aim of this study was to describe the plasma distribution of hsCRP concentration in healthy adult Nigerians and to estimate the proportions of those at high risk for cardiovascular disease. Materials and Methods: hsCRP glucose, total cholesterol, high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C) and triglycerides were measured in 120 adult Nigerians free of clinical and biochemical features, suggestive of cardiovascular disease and not on any form of hormonal therapy. The blood pressure, height and weight of the participants were also measured. hsCRP was measured by synthron CRP ultrasensitive enzyme-linked immunosorbent assay method, glucose was measured by the glucose oxidase method, while the lipid profile parameters were measured by enzymatic colorimetric methods. Results: hsCRP concentration ranged from 0.62 to 11.64 mg/L (median: 1.3 mg/L, mean: 2.3 mg/L, 95% confidence interval, 0.75-11.0 mg/L). About 81.7%, 15.0%, and 3.3% of the participants had hsCRP concentrations of less than 3 mg/L, 3-10 mg/L, and higher than 10 mg/ L, respectively. The plasma levels of glucose and lipid profile parameters were within the reference limits established at the Chemical Pathology Laboratory of Aminu Kano Teaching Hospital (AKTH). None of the participants was obese (mean body mass index was 18.6 kg/m 2 ). Conclusion: This study describes the plasma distribution of hsCRP in healthy Nigerian adults. The results obtained would be of further help in the risk-assessment of individuals for future cardiovascular disease.

Keywords: Cardiovascular-risk assessment, C-reactive protein, high-sensitivity assay


How to cite this article:
Yahaya IA. Distribution of plasma C-reactive protein measured by high-sensitivity assay in healthy Nigerian adults. Sub-Saharan Afr J Med 2014;1:26-30

How to cite this URL:
Yahaya IA. Distribution of plasma C-reactive protein measured by high-sensitivity assay in healthy Nigerian adults. Sub-Saharan Afr J Med [serial online] 2014 [cited 2021 Apr 16];1:26-30. Available from: https://www.ssajm.org/text.asp?2014/1/1/26/129306


  Introduction Top


C-reactive protein (CRP) is an acute phase reactant synthesized by the hepatocytes in response to cytokines released into the circulation by activated leucocytes. It is composed of five identical subunits arranged in a cyclic pentamer and belongs to the pentraxin family of proteins. [1]

CRP was discovered in 1930 by William Tillet and Thomas Francis [2] at the Rockefeller Institute. They extracted a protein from the sera of patients with pneumococcal pneumonia that co-precipitated with the C-polysaccharide derived from the cell wall of Streptococcus pneumoniae. This "C-reactive" activity was absent from the sera of healthy individuals.

Macleod and Avery [3] subsequently found this substance to be a protein and coined the term "acute phase" to characterize the serum of patients with various acute infections. Lofstrum [4] later found a similar acute-phase response in acute and chronic inflammatory conditions, and thus CRP became recognized as a nonspecific acute-phase protein.

CRP is stable in blood circulation with a half-life of 19 h. The plasma concentration of CRP rises rapidly (as much as 1000-folds or more) within 24-48 h, in response to most forms of tissue damage, infection, and other acute inflammatory events including autoimmune diseases and malignancy. [5] Consequently, CRP has been historically used to detect and predict the outcome of various infections, inflammatory and necrotic processes and to assess the efficacy of treatment for those processes. Mild inflammation and viral infections generally cause CRP concentrations to rise to between 10 and 50 mg/L, whereas active inflammation and bacterial infections generally result in concentrations between 50 and 200 mg/L. Concentrations higher than 200 mg/L are seen in more severe infections and in trauma. [6]

Laboratory, clinical, and epidemiological studies have demonstrated the role of inflammation in atherogenesis. These findings suggest that atherosclerosis is a chronic low-grade inflammatory condition that evolves as a result of a combination of biochemical, physical, and possibly infectious processes. [7],[8]

Several prospective studies have also shown that plasma hsCRP concentrations are increased many years in advance of first coronary and cerebrovascular events in healthy [9],[10],[11],[12] and high- risk individuals, [13],[14],[15] independent of the traditional risk factors. [16],[17] Thus, the assessment of CRP levels could provide a predictive means of assessing cardiovascular risk or the potential risk of recurrent cardiovascular events. [12],[18],[19]

The association between CRP and coronary heart disease (CHD) has also been found to be similar to that of traditional lipid risk factors. [17],[18],[19],[20] Consequently, the American Heart Association (AHA) and the Center for Disease Control and Prevention (CDC) clinically assessed a number of inflammatory markers and CRP was found to have characteristics considered most useful for practice. [21] Their guidelines suggest that CRP measurement be taken twice over a 2-week interval; CRP concentrations less than 1 mg/L are considered as "low risk", 1-3 mg/L, "average risk" and concentrations higher than 3 mg/L are considered "high risk". Values greater than 10 mg/L should be repeated with patients being examined for sources of inflammation or infection.

Since these ranges of CRP values include levels in otherwise apparently healthy individuals, high-sensitivity CRP (hsCRP) methods, with detection limits below that of routine assays of 3-5 mg/L, are required for cardiovascular risk assessment.

The development of hs-CRP, a stable and inexpensive assay, [22],[23] has increased the potential for obtaining more reliable determinants of circulating levels of this inflammatory cytokine, in cardiovascular risk assessment, particularly for those whose risk is intermediate, such as individuals with average levels of low-density lipoprotein cholesterol (LDL-C). This ultrasensitive assay is capable of measuring CRP at a concentration as low as 0.007 mg/L. [24] The analytical performance of the method has been validated previously. [25]

An algorithm for risk assessment of future coronary events that combines both CRP concentration and the ratio of total cholesterol (TC) to high-density lipoprotein-cholesterol (HDL-C) has been proposed. [26]

However, before screening of individuals at risk can be recommended, hsCRP distribution in healthy adults in the general population should be established.

This study, therefore, describes the distribution of hsCRP concentrations in 120 healthy Nigerian adults and also estimates the proportions of individuals at high risk for the development of cardiovascular disease.


  Materials and Methods Top


Study Center

This study was conducted at the Department of Chemical Pathology and Immunology, Aminu Kano Teaching Hospital, Kano-Nigeria.

Participants

A total of 120 healthy Nigerian adults were recruited for the study. They were made up of 58 males and 62 females (aged between 18 and 48 years) randomly selected from among the volunteered hospital staff, resident doctors, and undergraduate students on Students Industrial Working Experience Scheme (SIWES) attachment in the Laboratory Departments of Chemical Pathology, Hematology, Histopathology, and Microbiology. The SIWES students were drawn from various higher institutions of learning in Nigeria. All the participants were free of both history and clinical evidence of cardiovascular diseases and diabetes mellitus. None of them was on any form of hormonal therapy including contraceptives. Also, excluded from the study were cigarette smokers and alcoholics.

The participants were briefed on the objectives of the study and the biochemical investigations to be performed on their blood samples and their consent obtained accordingly.

Approval for the conduct of the study was obtained from the Ethical Committee of Aminu Kano Teaching Hospital.

Methods

Blood pressure was measured in mm Hg, in the sitting position after a 10 min rest. Height and weight were also measured in meters and kilograms, respectively, without shoes and heavy clothing and the body mass index (BMI) was calculated as weight (kg)/height [2] (meters 2 ).

About 5 mm of blood was collected from each of the participants by venepuncture using lithium heparin vacutainer tubes. All the samples were then centrifuged at 3000 g for 10 min and the separated plasma stored at −20°C until analysis. The plasma samples were later analyzed for CRP, glucose, TC, HDL-C, LDL-C, and triglycerides (TGs). All laboratory analyses were completed within 2 weeks of blood collection.

hsCRP was measured by the Syntron CRP ultrasensitive enzyme-linked immunosorbent assay kit. [25] It is a solid phase direct sandwich method. The assay used monoclonal anti-CRP antibodies and a calibrator that was traceable to the World Health Organization reference material.

Glucose was measured by the glucose oxidase method. [27]

TC and HDL-C and TGs were measured by enzymatic colorimetric methods. [28],[29],[30]

LDL-C was calculated using the Friedwald et al., [31] formular.

Statistical Analysis

Statistical analysis of the data was performed using the Statistical Package for Social Sciences (SPSS) version 16.0. The data obtained were shown as mean, standard deviation, percentages, and percentiles. For comparison of mean values, the unpaired t-test and Mann-Whitney U test were used.

Confidence interval (CI) was calculated using Bootstrap estimation between the 2.5 th and 97.5 th percentile. Significant difference was defined as P < 0.05.


  Results Top


The age distribution of the study participants shows that 99.2% of them was between 18 and 46 years of age [Table 1].
Table 1: Distribution of participants by age

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[Table 2] shows the BMI, glucose and lipid profile parameters of the participants. None of them was obese (mean BMI was 18.6 kg/m 2 ) and the values obtained for glucose and the lipid profile parameters were within the reference limits established at the Chemical Pathology Laboratory of AKTH.

The frequency distribution curve for the hsCRP was skewed to the right.
Table 2: Lipid profile, body mass index, and blood pressure of participants

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hsCRP distribution in percentiles is shown in [Table 3].
Table 3: High-sensitivity C-reactive protein distribution in percentiles

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hsCRP concentration ranged from 0.62 mg/L to 11.64 mg/L (median: 1.3 mg/L; mean: 2.3 mg/L). The 95% CI was 0.75-11.0 mg/L.

In addition, significant and independent association were observed between hsCRP and TC, hsCRP and LDL-C, hsCRP and TG, hsCRP and BMI (r = 0.51, 0.50, 0.58, 0.47, respectively).

There was no significant difference between the values obtained in the males and that of the females. About 81.7%, 15.0% and 3.3% of the participants had hsCRP concentrations less than 3 mg/L, 3-10 mg/L, higher than 10 mg/L, respectively.


  Discussion Top


This study involved individuals aged 18 years and above, with no features suggestive of cardiovascular disease, diabetes mellitus, and with normal lipid profile. None of the participants was on any form of hormonal therapy, including contraceptives. Hormonal therapy, whether it contains estrogen alone or in combination with progestin, is known to significantly increase CRP concentration. [32],[33],[34]

None of the participants was obese. The BMI calculated for the participants was within the reference range. The mean BMI was 18.6 kg/m 2 . However, a significant and independent association was observed between the BMI and the hsCRP of the participants. Significant correlations between hsCRP and BMI has been reported in the literature. [15],[35] Obesity is a known cause of increased level of CRP in plasma. [15],[35]

The distribution of hsCRP values in the healthy Nigerian males and females in this study was skewed to the right and were similar in both sexes; hence, the need for gender-specific cut-points does not arise for possible future cardiovascular risk assessment. A similar observation regarding the similarity of CRP distribution among Scottish men and women has been reported. [36] However in a German cohort, women had slightly but significantly higher hsCRP concentration compared with men. This observation was attributed to estrogen use among the female participants in the study. [36] Despite the similarities in the distribution of hCRP observed in both sexes by some authors, it has been shown to be predictive of future cardiovascular events in various populations with greatly differing absolute risk. [37]

In addition, the pattern of hsCRP distribution in the participants studied did not substantially differ from those reported from the United States of America, Europe, and Japan. [37],[38],[39] Furthermore, the range, mean CRP concentration and the 95% confidence interval (0.62-11.64 mg/L, 2.33 mg/L and 0.75-11.0 mg/L respectively) observed in this study compared with those described in other populations. [37],[38],[39] However, 18.3% of the participants had hsCRP concentration higher than 3 mg/L, which has been shown to be associated with an increased risk for future cardiovascular events. [21] This finding was particularly important as cardiovascular diseases have become a leading cause of morbidity and mortality in developing countries, including Nigeria. [40],[41] A small group of the participants (3.3%) had plasma hsCRP concentrations higher than 10 mg/L, indicating an ongoing high-grade inflammatory process.

Study Limitation

This study involved students from selected Nigerian Universities and hospital staff. This could constitute a statistical bias in respect of what actually obtains in the general population. Therefore, nationwide community-based epidemiological studies on this subject matter are required to validate the findings of this study.


  Summary/Conclusion Top


This study described the distribution of hsCRP in 120 healthy Nigerian adults.

Data information included both genders. To avoid confounding for disease outcome and drugs, individuals with features of cardiovascular diseases, diabetes mellitus, women on oral contraceptives or hormonal therapy, cigarette smokers and alcoholics were excluded and the study covered a wide age range.

Furthermore we looked for associations between hsCRP and BMI, TC, LDL-C, TG.

In all samples, hsCRP distribution was skewed to the right and was similar in the adult men and women studied.

The range, mean, and CI of CRP were 0.62-11.64, 2.3, and 0.75-11.0 mg/L, respectively. About 18.3% of the participants were found to have plasma hsCRP concentrations higher than 3 mg/L.

In conclusion, due to the current interest in the use of hsCRP in assessing the risk of future cardiovascular events, the results obtained from this study will be useful to both researchers and clinicians alike.

 
  References Top

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