Positive Correlation of CRP and Fibrinogen Levels as Cardiovascular Risk Factors in Early Stage of Continuous Ambulatory Peritoneal Dialysis Patients

Abstract

We aimed to study the relationship between the C-reactive protein (CRP), albumin, and fibrinogen as cardiovascular risk factors in continuous ambulatory peritoneal dialysis (CAPD) patients, in the early stage of their therapy. The study included 21 CAPD patients as the study group (SG) and age- and sex-matched 21 healthy patients as the control group (CG). History and physical exam data were obtained for all cases, and demographic baseline characteristics were taken. Twelve-hour fasting serum levels of glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglyceride, total protein, albumin, hemoglobin, CRP, and fibrinogen were obtained.

There was no statistically significant difference between the SG and CG in baseline characteristics, including age, sex, body mass index (BMI), smoking, and family history of cardiovascular disease. However, diabetes mellitus (DM) and hypertension (HTN) were significantly more common among the study group. The average total protein, albumin, and hemoglobin levels were significantly lower, and the CRP and fibrinogen levels were significantly higher (p < 0.001) in the SG. A positive correlation was seen (r = 0.443, p < 0.05) among CRP and fibrinogen levels in SG. There was no correlation among the other parameters in SG. For CG, there was no correlation seen for any studied parameters. When patients with and without cardiovascular disease (CVD) were compared, no correlation was seen between CRP and other parameters. A positive correlation of CRP and fibrinogen levels as cardiovascular risk factors was shown in early stage of CAPD patients. The CAPD patients with elevated levels of CRP and fibrinogen should receive close follow-up for cardiovascular disease prevention.

Keywords:

• chronic renal disease
• coronary artery disease
• anticardiolipin antibodies
• echocardiography
• coronary angiography

INTRODUCTION

Cardiovascular disease (CVD) plays a major role in morbidity and mortality of end stage renal disease (ESRD) patients. A significant number of ESRD patients already has coexisting CVD, and others are under a major risk of developing CVD when they start for dialysis. It is shown that aggressive modification of cardiovascular risk factors in early stage in ESRD reduces the CVD development.[1],[2] Thus, there is more interest and research in understanding the pathogenesis of CVD development in ESRD patients.

The classical major risk factors for CVD, such as family history, hypertension, diabetes, smoking, and hyperlipidemia have been shown to be present frequently even in the earliest stage of ESRD.[2],[3]

There is more recent evidence that shows that inflammation plays a significant role in the pathogenesis of atherosclerosis.[4–7] A recent study provides evidence that dietary discretion and inflammation may increase propensity for CVD.[7] Some studies suggested elevated CRP and protein levels and malnutrition correlated with a higher prevalence of CVD in ESRD patients who have not started dialysis yet.

Furthermore, the effect of aspirin in reducing the myocardial infarction risk is directly related to CRP levels, signifying the beneficial role of anti-inflammation in prevention of CVD.[6–9]

We aimed to study the correlation of the inflammatory markers (CRP, fibrinogen, and albumin) as CVD risk factors in patients diagnosed with ESRD who just started to receive CAPD in our medical center.

PATIENTS AND METHODS

The study protocol was approved by the ethical committee of the Medical Center of The Medical Faculty of Zonguldak Karaelmas University (ZKU). Twenty-one patients (10 female, 11 male) recently diagnosed with ESRD and just starting to receive CAPD at ZKU's Department of Internal Medicine were included in the study. Twenty-one age- and sex-matched healthy patients were included as control group (CG).

Patients who expired in the first three months of receiving CAPD, who left our center and continued to receive CAPD in another center, or whose CAPD terminated for any reason were excluded from the study. All patients' history and physical exams from CVD risk factors standpoint were obtained, and the laboratory tests were performed in the first three months of their CAPD therapy.

All patients had electrocardiography (ECG) cardiac catheterization performed when necessary. Diagnostic and therapeutic measurements were applied by the Department of Cardiology at ZKU Medical Center. CAPD patients were also evaluated in two subgroups: CAPD patients with coronary artery disease and those without coronary artery disease.

CVD risk profiles of patients were obtained including age, sex, personal history, family history, height, weight, and hypertension. Twelve-hour overnight fasting serum levels of glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglyceride, total protein, albumin, and CRP were obtained.

Then, 1.36% and when necessary 3.86% glucose-concentrated two-liters of peritoneal dialysis fluid was used three to four times a day in CAPD patients. All CAPD patients received a renal diet, including 30–35 kcal/kg/day, 1.2–1.4 g/kg/day protein, 1000–1500 mg/day calcium, 600–700 mg/day phosphorus, and 200–250 mg/day magnesium. BMI was calculated as weight (kg)/height² (m).

The Kt value at CAPD is the 24 hr output of dialysis fluid volume (DV): where IBW is the ideal body weight and Cr is the residual renal clearance (L/day).

Serum total cholesterol, HDL cholesterol, LDL cholesterol, total protein, and albumin levels were studied at the Biochemistry Laboratory of the ZKU Medical Center. Serum high sensitivity CRP (hs-CRP) was measured with a prespec device using the Dade-Behring kit. The normal cut off value of 3.0 mg/dL was used. Subjects with high CRP underwent an evaluation for the possible presence of infectious disease, erythrocyte sedimentation rate, and complete blood count. When infection was encountered, an appropriate treatment was applied, and after 21 days of completion of the treatment, a new level of serum CRP was obtained.

Fibrinogen was measured via an AMOX 200 device by using sigma diagnostic kit. Normal cut-off value of 175–400 mg/dL was used.

Statistical Analysis

Statistics were analyzed using the Statistical Package for Social Science (SPSS for Windows, version 11.0). The results were reflected with average ± SD (standard deviation). Mann-Whitney U test was utilized for a comparison of the average values among the groups and for subgroup analysis between the subgroups with CVD and without CVD.

Spearman's rho correlation test was applied in evaluating the correlation between CRP and the other parameters. The results are utilized in 95% confidence interval, and a significant p value less than 0.05 was designed as significant.

RESULTS

The study group that included CAPD patients consisted of 11 males and 10 females. The average age was 57.47 ± 19.06 (age range of 17–88). The healthy control group consisted of 11 male and 10 female with an average age of 58.47 ± 9.03 (age range at 42–62). The etiology of chronic renal failure of the CAPD patients is shown in Table 1.

Table 1 Etiology of renal failure in CAPD patients

Renal failure etiology	Number of patients (n)	%
Diabetic nephropathy	8	38.1
Chronic glomerulonephritis	4	19.1
Hypertensive nephropathy	3	14.3
Chronic pyelonephritis	2	9.5
Obstructive nephropathy	4	19.1
Total	21	100

Table 2 included the group characteristics of CAPD patients and the control group. It shows the average age, sex, BMI, smoking status, family history, diabetes, hypertension, total cholesterol, HDL-C, LDL-C, triglycerides, total protein albumin, hemoglobin, and C-reactive protein (CRP), fibrinogen, as well as the statistical analysis.

Table 2 Baseline characteristics and serum levels of parameters of the groups

CAPD (n = 21)	Control (n = 21)		p
Age (years)	57.47 ± 19.06	58.47 ± 9.03	>0.05
Sex (M/F)	10/11	10/11	>0.05
BMI (kg/m^2)	23.72 ± 4.83	24.82 ± 3.91	>0.05
Dialysate volume (liter)	9.2 ± 1.0	—	—
Kt/V	2.2 ± 0.4	—	—
Family history	9	7	>0.05
Diabetes	8	0	<0.001
Hypertension	7	0	<0.001
Total cholesterol (mg/dL)	182.04 ± 47.92	195.23 ± 31.96	>0.05
HDL cholesterol (mg/dL)	41.28 ± 13.05	48.42 ± 15.59	>0.05
LDL cholesterol (mg/dL)	111.47 ± 31.48	120.23 ± 30.28	>0.05
Triglycerides (mg/dL)	149.95 ± 79.94	138.80 ± 71.92	>0.05
Total protein (g/dL)	5.8 ± 1.02	7.33 ± 0.46	<0.001
Albumin (g/dL)	2.9 ± 0.77	4.36 ± 0.37	<0.001
Hemoglobin (g/dL)	10.79 ± 1.86	13.83 ± 1.53	<0.001
CRP (mg/dL)	23.28 ± 3.45	3.05 ± 2.28	<0.001
Fibrinogen (mg/dL)	516.38 ± 168.51	331.9 ± 61.34	<0.001

There was no statistically significant difference in between the two groups in regard to average age, sex, BMI, smoking status, and family history (p > 0.05). However, diabetes and hypertension were significantly more prevalent in CAPD patients (p < 0.001).

There was no statistically significant difference in average values of total cholesterol, HDL-C, LDL-C, or triglycerides in between the groups (p > 0.05). The average values of total protein, albumin, and hemoglobin were significantly lower, while CRP and fibrinogen values were significantly higher in the CAPD patients (p < 0.001).

There was no correlation between the parameters in the control group. A positive correlation of CRP and fibrinogen levels (r = 0.443, p < 0.05) was shown in CAPD patients. There was no correlation among other parameters in CAPD patients.

CRP and fibrinogen level were elevated in 71.4% and in 80.9% in turn in CAPD patients. Albumin levels were low in 80.9% of CAPD patients.

Nine patients in the CAPD group were shown to have coronary artery disease by family history, physical exam, ECG, echocardiography, and coronary artery angiography. Of these nine patients, five were diagnosed with coronary artery disease before starting CAPD.

A subgroup analysis was performed among the CAPD patients with and without coronary artery disease. Group characteristics and average values of the parameters of these two subgroups are shown in Table 3.

Table 3 Baseline characteristics and serum levels of parameters of the subgroups

CAPD without CAD (n = 12)	CAPD with CAD (n = 9)		p
Age (years)	52.58 ± 21.64	64 ± 13.46	>0.05
Sex (F/M)	5/7	5/4	>0.05
BMI (kg/m^2)	22.70 ± 4.26	25.07 ± 5.45	>0.05
Dialysate volume (liter)	9.2 ± 1.0	9.1 ± 1.1	>0.05
Kt/V	2.2 ± 0.4	2.2 ± 0.3	>0.05
Smoking	3	2	>0.05
Family history	5	4	>0.05
Diabetes	4	4	>0.05
Total cholesterol (mg/dL)	186.25 ± 45.06	181.77 ± 54.31	>0.05
HDL cholesterol (mg/dL)	40.91 ± 13.62	41.77 ± 13.05	>0.05
LDL cholesterol (mg/dL)	113.75 ± 33.82	108.44 ± 29.79	>0.05
Tryglycerides (mg/dL)	142.91 ± 50.67	159.33 ± 110.79	>0.05
Total protein (g/dL)	5.9 ± 1.09	5.6 ± 0.95	>0.05
Albumin (g/dL)	3.21 ± 0.81	2.48 ± 0.48	>0.05
Hemoglobin (g/dL)	10.97 ± 2.23	10.54 ± 1.3	>0.05
CRP (mg/dL)	12.13 ± 3.01	38.16 ± 4.54	<0.05
Fibrinogen (mg/dL)	455.41 ± 182.69	597.66 ± 109.95	<0.05

There was no statistically significant difference among the two subgroups in regard to age, sex, BMI, smoking status, family history, diabetes, or hypertension (p > 0.05). There was also no statistically significant difference between the two subgroups in regard to total cholesterol, HDL-C, LDL-C, triglycerides, total protein, albumin, or hemoglobin (p > 0.05). However, CRP and fibrinogen levels were significantly higher in the CAPD patients with coronary artery disease. There was no correlation between CRP and other parameters in CAPD patients without coronary artery disease.

DISCUSSION

Cardiovascular disease is the most common cause of mortality among end stage renal disease patients regardless of their primary renal disease, age, sex, race, and ethnicity. The cardiovascular disease-related mortality ratio among end stage renal disease patients is higher than the general population for all age groups. This is more pronounced in younger patients.[10] Cardiovascular disease prevalence is increased in end stage renal disease because the risk factors for arteriosclerosis as such hypertension and diabetes are more common.

End stage renal disease patients have similar symptoms of myocardial ischemia like other patients without renal failure, yet silent ischemia is more common in diabetics. Diagnostic work-up and treatment of cardiovascular disease are similar. Cardiac catheterization is the gold standard in identifying coronary artery disease.

There is no indication for coronary artery disease screening among end stage renal disease patients except for the patients who are considered for renal transplant.[11] There is increased risk for cardiovascular disease even in the early stage of renal transplantation, although this risk continues to rise at the later years.[5],[12],[13]

We obtained a history and physical exam data and echocardiography (ECG) for our patients to screen for coronary artery disease. Cardiac catheterization was performed by the Department of Cardiology when indicated. There were five patients diagnosed with coronary artery disease prior to starting CAPD treatment and four patients identified with coronary artery disease after initiation.

C-reactive protein (CRP) has been identified as major acute phase reactant for a long time. The acute phase of inflammatory response is characterized by physiological changes in the presence of stimulation such as infection and trauma. During this inflammatory response, when there is an increase in levels of plasma proteins, such plasma proteins are called as positive acute phase reactants; if there is decrease, then they are called negative acute phase reactants.[14],[15] These changes in plasma levels occur because of varying secretion of hepatocytes. CRP level may increase up to one thousand times during the acute phase.[14–16]

Multiple acute phase reactants have been identified. Acute phase proteins that are induced by cytokines and other extracellular signaling molecules such as IL-6, ILβ, TNF-α, interferon-γ, transforming growth factor β (TGF-β), and IL-8 are among the important cytokines that play a role in inflammation.[17],[18] Cytokines are produced by the regional macrophages and monocytes and activates the hepatocytes to secret acute phase proteins.[16]

CRP is one of the most sensitive acute phase proteins and is a pentamer with 115kDa molecular weight. Its half-life is 19 hours.[14],[19] Although its full function is not clarified yet, it may act as cleaning factor for endotoxin and opsonized bacterial degradation products.

A similar observation can be made among the uremic patients and healthy subjects. There is faster and higher level of response in uremic patients. It has been shown for many years that CRP may play a role as a risk factor in the future independent from the acute incident.[20–22]

Negative acute phase reactants as such albumin, fibrinogen, apolipoprotein A-1, and lipoprotein (a) and positive acute phase reactants have interrelations with CRP; most of these proteins may add incremental values and/or act as important risk factors for cardiovascular disease.[23]

CRP may be a more sensitive indicator of morbidity than many other acute phase reactants, including albumin. Baseline values of CRP may be used as an independent predictor for myocardial infarction, stroke, and peripheral vascular disease.[14],[21]

CRP levels are elevated when there is an inflammation, infection, or tissue damage. CRP levels may increase up to 500–1000 times of normal values depending on strength of the inflammatory activity.[14] Standard CRP measurement may be sufficient for a clinically manifested inflammatory incident. However, standard CRP measurement is not sufficient to identify cardiovascular risk factors in healthy subjects. Thus, high sensitivity-CRP measurement has been developed (hs-CRP).[14],[24]

Hs-CRP levels may help in identifying the first or recurrent coronary incidents and indicate the inflammatory activity in the vascular system. Baseline values of CRP may be used as an independent predictor for myocardial infarction, stroke, and peripheral vascular disease.

CRP levels may help in the risk stratification of the patients with acute coronary syndrome. Patients with elevated hs-CRP level may be at higher risk for cardiovascular incident.[25–27] We found no difference with demographic characteristics in between our healthy control group and CAPD patients in regards to age sex, BMI, smoking status, and family history, while there was diabetes in 38.1% and hypertension in 33.3% of CAPD patients. We identified diabetes in 38.1% and hypertension in 14.3% of our patients as the primary etiology in their end stage renal disease.

There was no difference in demographic characteristics in between the two subgroups (the CAPD patients with coronary artery disease and the CAPD patients without coronary artery disease), including age, sex, BMI, smoking status, family history, diabetes, and hypertension. We saw no significant difference between the two subgroups because the study was conducted at an early stage of CAPD.

It is currently unknown whether acute phase reactants are a mere marker of arteriosclerosis or play a role in the start and progression of arteriosclerosis. Nevertheless, the most recent evidence shows that CRP may be related to thrombogenesis. CRP, IL-6, fibrinogen, and TNFα markers of inflammation may enhance the arteriosclerosis.[28]

Fetuin-A, a calcification inhibitor in serum, gained attention recently. Serum level of fetuin-A is decreased during the chronic inflammation; patients with low fetuin-A levels have less survival when compared with patients with normal or elevated levels of fetuin-A.[29]

Increased levels of CRP have been shown that may predict cardiovascular or all cause mortality in CAPD patients.[30],[31] Moreover, elevated CRP levels may indicate an increased risk of future nonfatal myocardial infarction and cardiovascular incident.[32]

A positive correlation has been shown in pre-dialysis CRP levels and carotid artery intimal thickness progression.[21] Negative acute phase reactants such as albumin, fibrinogen, Apo A-1, Lp(a), and serum amyloid A have a correlation with CRP. Some of these proteins may predict or cause cardiovascular disease in both hemodialysis and CAPD patients.[13],[33]

In our study, CRP and fibrinogen levels were elevated in 71.4% and 80.9% in turn in CAPD patients. Albumin levels were low in 80.9% of CAPD patients. The Borazan et al. study[34] included 16 CAPD and 52 hemodialysis patients. They showed that CRP is elevated in 77.7% of CAPD patients and 48.1% of hemodialysis patients. They also showed a negative correlation in CRP levels and Kt/V and albumin levels.

We did not find a correlation with CRP and Kt/V. One potential explanation of this may be related to CAPD treatment duration. While our study was conducted at an early stage of the CAPD, Borazan et al.'s study showed that the average CAPD duration was 17.3 months.[34]

In another study, Borazan et al.[35] showed that CRP levels were elevated in the beginning and in the third months of the CAPD treatment when compared to control patients. They found no further increase after three months in CRP levels.

There is both peritoneal irritation and reduced elimination of cytokines in CAPD patients, which may be responsible for elevated CRP levels in CAPD patients.[36] We found statistically significantly higher CRP and fibrinogen levels and lower levels of albumin in CAPD patients when compared to control group in or study.

When we compared the two subgroups, we found higher CRP and fibrinogen levels in CAPD patients with coronary artery disease as opposed to CAPD patients without coronary artery disease. There was no difference in albumin levels between the two subgroups. Our findings are parallel with the current literature.

Fibrinogen is an acute phase reactant like CRP. Increased levels of fibrinogen may cause increased coagulation activity, platelet aggregation, and vascular endothelial dysfunction, and may act as an independent risk factor for cardiovascular disease. Weight loss, exercise, smoking cessation, and benzofibrates may reduce fibrinogen levels. There has yet been any specific theaurepethic agent that alters fibrinogen levels.[37],[38]

Serum albumin level is a negative phase reactant that is reduced in inflammation. Serum CRP and other acute phase reactants are elevated in patients with chronic renal failure and low albumin levels. Albumin concentrations are decreased in chronic renal failure patients because of reduced albumin synthesis, given ongoing inflammation, insufficient protein and calorie intake, and increased catabolic state.

It has been show that there is a strong negative correlation between serum CRP and albumin level. There has been a strong relationship between hypoalbuminemia and mortality.[13],[33],[39] As a result, we found statistically significantly elevated levels of CRP and fibrinogen and lower levels of albumin in CAPD patients in comparison to the control group in our study. Elevated CRP and fibrinogen levels are cardiovascular risk factors. Because there is increased incidence of cardiovascular disease and an already higher prevalence of risk factors in CAPD, we believe that CAPD patients need closer follow-up and screening for cardiovascular disease.