Evaluation of high-sensitivity C-reactive protein in acute asthma.

BACKGROUND: High sensitivity C-reactive protein (hs-CRP) is an inflammatory marker known to be related to inflammation, infection, and cardiovascular diseases. The aim of this study was to evaluate hs-CRP level in serum of asthmatics and its relationship with pulmonary function tests, serum IgE levels, and peripheral blood white blood cell (WBC) counts.
MATERIALS AND METHODS: The under study subjects were 108 patients with acute asthma and 93 healthy volunteers. The levels of hs-CRP of 108 patients with acute bronchial asthma and 93 non-asthmatic control subjects were measured. Spirometry, serum immunoglobulin-E (IgE) measurement, and WBC counts were done for patient and control groups.
RESULTS: The mean serum hs-CRP levels were significantly higher in patients with acute asthma compared with controls (5.47±7.33 mg/l versus 1.46± 1.89 mg/l, p < 0.001). Among asthmatic patients, mean hs-CRP levels were not correlated with indices of pulmonary function tests (forced expiratory volume in one second, forced vital capacity and forced mid-expiratory flow), serum IgE level, eosinophil count or WBC count.
CONCLUSION: Serum C-reactive protein levels measured by high-sensitivity assays increase in acute asthma and may be useful as a diagnostic tool for detecting and monitoring inflammation in these patients. In our study on patients with acute asthma, no significant correlation was revealed between hs-CRP and pulmonary function tests, total serum IgE, or peripheral blood white blood cell counts.

INTRODUCTION

Asthma is a condition characterized by variability in airflow obstruction, fluctuation of symptoms, and changes in the level of bronchial responsiveness and airway inflammation. CRP is one of the most characteristic markers of the inflammatory process. The monitoring of CRP levels is a good diagnostic tool and is very useful for the assessment of early inflammation, treatment monitoring and acute-phase diseases (1).

It is well known that CRP increases during infection and autoimmune disorders (2). In recent years, there have been some reports concerning the measurement of serum levels of hs-CRP as a useful tool for detecting systemic inflammation in asthma (3, 4).

Several studies have indicated a positive correlation between asthma and increased CRP levels (5–8). A positive relationship has been reported between raised CRP levels and current asthma (5, 6), respiratory impairment (9–12), and bronchial hyper-responsiveness (13).

In this study, we evaluated the relationship of serum hs-CRP level as an indicator of inflammation among asthmatic patients with pulmonary function tests, total serum IgE, and peripheral white blood cell (WBC) counts.

MATERIALS AND METHODS

This study was carried out on adult patients treated for acute asthma in a private clinic between March 2007 and February 2009. In all patients, the treatment was adjusted according to the level of disease severity (14). The inclusion criteria for the study consisted of no systemic infectious diseases, no malignant diseases, no auto-immune disorders, no abnormal hepatic or renal function test results, and no regular use of oral or systemic corticosteroids. Patients who had respiratory tract infections in the last month before the study were excluded from this study. Before initiation of treatment, blood samples were obtained for measurement of hs-CRP levels, total serum IgE level, peripheral white blood cell counts and eosinophil count. Measurement of hs-CRP, total serum IgE level, white blood cell count and eosinophil count was performed in Dr. Ehteram laboratory. Total serum IgE level (IU/ml) was measured by immunoassay (Monobind, INC. Costa Mesa, CA, USA). The concentrations of hs-CRP in serum were determined using a sensitive CRP assay (Monobind, INC. Lake Forest, CA, USA).

Spirometry was measured at baseline, using a spirometer (Fukuda, ST 95). The subjects were adult asthmatic patients with 50-85% of predicted FEV1, which were recruited from out-patients referred to the office for treatment. An informed consent was obtained from all participants before the studies were carried out, and the Clinical Research Ethics Committee of Kashan University of Medical Sciences approved this study. The diagnosis of asthma was made on clinical grounds and required objective criteria of reversible airway obstruction as an improvement in FEV1 ≥ 12% (and ≥ 200 ml) after inhalation of a short-acting β2-agonist defined by the American Thoracic Society (15). Results were obtained for forced vital capacity (FVC), FEV1, FEV1/FVC percentage and forced expiratory flow at 25-75% of FVC (FEF 25-75%).

Ninety-three healthy volunteers comprised our normal control group. They had no respiratory tract infection in the past 3 months prior to the study, and no other significant illnesses. All subjects were nonsmoker and non-atopic. All subjects had a complete history, physical examination and spirometry. Blood samples were collected to determine serum IgE level, eosinophil count and WBC.

Data were expressed as mean ± standard deviation. The Kolmogorov-Smirnov test was used for distribution of quantitative variables. Comparisons of serum hs-CRP levels in the two groups were performed using analysis of variance for normally distributed data and the Mann-Whitney U test, Kruskal-Wallis test, or Wilcoxon signed rank test for not normally distributed data. The relationships between normally distributed variables were examined using the Pearson's correlation coefficient. Correlations between serum hs-CRP levels and other variables were determined using the Spearman rank correlation coefficient when the data was not normally distributed. Statistical differences were considered to be significant at P<0.05. Statistical analysis was performed using SPSS version 15.0 software.

RESULTS

Table 1 shows the clinical characteristics of the asthmatic and control subjects. The controls (46 men and 47 women; mean age 34.05 years) were healthy volunteers who had an office visit for a routine check-up during the mentioned period. They had no history of allergic disease, infection, or systemic disease for at least 3 months before the blood was collected.

Table 1

Characteristics of the study subjects

	Asthmatic Subjects	Control Subjects	P-values	CI 95%
Sex (M/F)	64/44	46/47
BMI	26.07±4.7	26.6±5	0.89
Age (years)	38.22±11.94	34.05±10.6	0.23
FVC (Lit)	2.87±0.96	4.1±0.94	<0.001	-1.50 -.96
FVC (% predicted)	74.29±16.68	104.61±9.02	<0.001	-34 -26.7
FEV1 (Lit)	1.09±0.69	3.47±0.82	<0.001	-1.78 -1.35
FEV1 (% predicted)	58.4±16.56	103.8±9.69	<0.001	-49.12 -41.68
FEF25-75% (L/sec)	1.28±0.61	3.79±1.11	<0.001	-2.76 -2.25
FEF 25-75% (%pred)	30.99±13.19	90.85±20.82	<0.001	-64.81 -54.91
Hs-CRP (mg/l)	5.47±7.33	1.46±1.89	<0.001	2.57 5.47
Total serum IgE (IU/ml)	212.4±206.6	127.1±132.7	0.001	37.52 132.92
White blood cell count (mm 3 )	8907±2436	8088.7±2574.1	0.02	120.6 1515.8
Blood eosinophil count (mm 3 )	2.59±1.65	2.10±1.25	<0.001	0.07 0.90

FEV1: Forced expiratory volume in one second; FVC: Forced vital capacity; FEF25–75%: Forced midexpiratory flow;% pred: Percentage of the predicted value; BMI: Body mass index

When studying the general characteristics of all studied subjects, it was found that there was no difference in the mean age between asthmatic patients and control subjects (38.22±11.94 and 34.05±10.6, respectively, P = 0.23).

There was no significant difference in BMI among the asthmatic patients and healthy controls (P = 0.89). The mean plasma hs-CRP levels were significantly elevated in patients with acute asthma compared to control subjects (5.47±7.33 mg/l, and 1.46±1.89 mg/l, respectively; p < 0.001) (Figure 1). No significant association was detected between the hs-CRP level and the FEV1 (% predicted) (R = -0.151, P = 0.118), FVC (%predicted) (R = -0.188, P = 0.051) or FEF25–75% (% predicted) (R = -0.067, P = 0.491) values (Table 2). There was no statistically significant correlation between hs-CRP in serum and other studied parameters in any of the studied groups of asthmatics and control subjects. The results are presented in Table 2.

Figure 1

Concentrations of mean hs-CRP in asthmatic patients and healthy control subjects

Table 2

Relationship between serum high-sensitivity C-reactive protein (hs-CRP) levels and pulmonary function test and other biochemical indexes in patients with asthma

High-sensitivity C-reactive protein
	Asthmatic patients (n = 108)		Control patients (n = 98)
	r	P value	r	P value
Age (years)	-0.037	0.7	0.156	0.136
BMI	0.259	0.007	0.214	0.040
FVC (Lit)	-0.143	0.139	-0.203	0.051
FVC (% predicted)	0.188	0.051	-0.097	0.357
FEV1 (lit)	-0.135	0.163	-0.171	0.101
FEV1 (% predicted)	-0.151	0.118	-0.042	0.687
FEF25–75%(L/sec)	-0.073	0.453	-0.007	0.950
FEF25–75% (% pred)	-0.067	0.491	0.125	0.232
Total serum IgE (IU/ml)	-0.156	0.107	-0.048	0.650
White blood cell count (mm 3 )	-0.079	0.715	0.107	0.306
Blood eosinophil count (mm 3 )	-0.171	0.415	-0.124	0.237

FEV1: Forced expiratory volume in one second; FVC: Forced vital capacity; FEF25–75%: Forced midexpiratory flow;% pred: Percentage of the predicted value; BMI: Body mass index.

DISCUSSION

It has been shown that in patients with acute asthma, serum levels of hs-CRP were increased compared with healthy controls, and no significant correlations were found between hs-CRP levels and indices of pulmonary function, total serum IgE levels, white blood cell count or eosinophil count.

In asthma, the importance of airway inflammation has been well established. Beside the airway inflammation, systemic inflammation may exist in asthma (5, 16, 17). In recent studies concerning hs-CRP assessment in asthma, the authors have focused on the possibility of using hs-CRP measurements as a marker for low-grade systemic inflammation in asthma. It is worth noting that CRP could also serve as a mediator of inflammation. CRP could elicit macrophage activation (through interaction with Fc receptors for antibodies) (18). CRP inhibits T- lymphocyte binding to antigen receptors (TCR). It has been demonstrated that CRP acts directly on monocytes and neutrophils through recognizing CRP-R receptors on their surface (19). The population of monocytes with specific surface antigenic determinants with an affinity to CRP has also been described (20). As an easily obtained and relatively inexpensive blood test, hs-CRP might be a surrogate marker of airway inflammation.

Several factors other than the presence of asthma might affect serum levels of hs-CRP. Not only the presence of cardiovascular disease or diabetes mellitus but also obesity itself is associated with increased plasma hs-CRP levels, which may be due to adipocyte-derived interleukin-6 (6, 21, 22). Aging also results in elevated hs-CRP levels, and smoking cessation leads to a reduction in hs-CRP level (23).

Regarding the possibility of using hs-CRP measurements to assess subclinical, systemic inflammation in asthma, Kony et al, in a population-based study has shown associations of increased levels of serum hs-CRP with a high frequency of airway hyper-responsiveness and low forced expiratory volume in 1 second (FEV1) (13). They concluded that systemic inflammation can be associated with respiratory impairment (13). In a study, Sävykoski et al. demonstrated that serum hs-CRP levels were significantly higher in patients with mild-to moderate asthma than in healthy controls (7). Olafsdottir et al. have demonstrated that raised serum levels of hs-CRP are associated with respiratory symptoms in asthmatic patients (8). Takemura et al. have found that in patients with steroid-native asthma, serum levels of hs-CRP were increased compared with healthy volunteers, and correlated negatively with indices of pulmonary function and positively with number of sputum eosinophils (3). Shaaban et al. in a population-based study suggested that increases in serum CRP concentration over time are associated with a significant decline in pulmonary function, consistent with the hypothesis that low-grade systemic inflammation is associated with pulmonary impairment (24).

In the present study, patients with acute asthma showed increased serum hs-CRP levels compared with healthy controls. Moreover, no significant correlation was observed between serum hs-CRP levels and FVC, FEV1, FEF25–75%, total serum IgE, white blood cell or eosinophil counts. The present result confirmed the presence of systemic inflammation in asthma as was previously shown (5, 16, 17) and indicated an association between systemic inflammation and airway inflammation. This observation was in accord with the previous studies performed by Qian et al. in which the highest serum CRP levels were demonstrated to be in patients with severe persistent asthma (25).

Recently in a study conducted by Ramirez et al. on patients with mild asthma, no significant correlation was detected between hsCRP and FEV1 (correlation coefficient = 0.07) (26). In the current study correlation coefficients for hs-CRP vs. FEV1 was -0.151. In another study performed on children with asthma of various severity degrees (mild persistent, moderate persistent, and severe persistent), hs-CRP, leukotriene B and leukotriene C were gradually increased from mild to moderate and severe (27).

CONCLUSION

Increase in serum C-reactive protein levels measured by high-sensitivity assays may be associated with airflow obstruction in acute asthma, and may be useful as a sensitive marker and a diagnostic tool for detecting and monitoring airway inflammation in patients with acute asthma. Subsequently, hs-CRP can be considered as a surrogate marker of airway inflammation.