Development of a new microparticle-enhanced turbidimetric assay for C-reactive protein with superior features in analytical sensitivity and dynamic range

A twin study of C-Reactive Protein compared to other risk factors for coronary heart disease

Coronary heart disease (CHD) tends to cluster in families, and several established risk factors for the disease are to some extent inherited. Inflammation plays a key role in the development of atherosclerosis and CHD. A low-grade inflammation may be detected by highly sensitive C-Reactive Protein (CRP) determination, which is strongly associated to CHD. In order to uncover any role of genetics in low-grade inflammation, we measured CRP in healthy monozygotic twins. The within-pair correlation coefficient of CRP was 0.40, suggesting an important genetic contribution to the control of CRP level. CRP correlated significantly to other CHD risk factors like body mass index (BMI), systolic blood pressure, diastolic blood pressure, plasma fibrinogen, serum high-density lipoprotein cholesterol, plasma homocysteine, and serum triglycerides. Of these variables, BMI was most significantly associated to CRP in a linear multiple regression analysis. We conclude that CRP level (reflecting a low-grade inflammation) exhibits a moderate, but significant degree of heritability. The association between CRP and BMI, which has a larger degree of heritability, could partly explain the heritability of serum CRP level.

Analytical performance of a highly sensitive C-reactive protein-based immunoassay and the effects of laboratory variables on levels of protein in blood

C-reactive protein (CRP) is an acute-phase reactant whose levels increase in response to a variety of inflammatory stimuli. Elevated levels in serum are observed after trauma, tissue necrosis, infection, surgery, and myocardial infarction and are associated with an increased risk of cardiovascular disease. CRP levels are also elevated in noninflammatory states, such as obesity, sleep disturbances, depression, chronic fatigue, aging, and physical inactivity. In this study, the performance of a highly sensitive CRP enzyme immunoassay was evaluated, along with common laboratory variables (specimen type, processing time, and storage conditions) that may influence measured blood concentrations of CRP. The measurement range of the assay was from 0.4 to 50 microg/liter. Total imprecision (coefficient of variation) ranged from 8.1 to 11.4%. CRP levels obtained with the enzyme immunoassay were highly correlated with those obtained with an automated immunonephelometric assay. Comparable results were obtained for plasma (heparin and EDTA treated) and serum samples, and levels were unaffected by delays in sample processing and storage temperature. CRP levels were also unaffected by up to seven freeze-thaw cycles. The median CRP concentration in healthy adults was determined to be 0.94 mg/liter, with a 95% working reference interval of 0 to 6.9 mg/liter. In view of these data, we recommend that serial serum or plasma samples for CRP should be stored at 4 degrees C for short periods of time or at -70 degrees C for longer periods and tested within the same run to minimize interassay variability.

Intestinal and systemic immune responses to an oral cholera toxoid B subunit whole-cell vaccine administered during zinc supplementation

Zinc plays a critical role in the normal functioning of the immune system. We investigated whether zinc sulfate administered orally to adult zinc-replete volunteers modulates systemic and intestinal immune responses to an oral killed cholera toxoid B subunit (CTB) whole-cell cholera vaccine. The 30 participants were immunized twice, with a 17-day interval. The vaccinees in the intervention group ingested 45 mg of elemental zinc thrice daily for 9 days starting 2 days before each vaccine dose. The median serum anti-CTB immunoglobulin A (IgA) and IgG responses from day 0 to day 30, i.e. after two vaccine doses, were 13-fold lower (P value for identical distribution, <0.005) in the zinc-supplemented compared to the nonsupplemented vaccinees. The median serum vibriocidal responses from baseline to after one (day 0 to day 17) and two (day 0 to day 30) vaccine doses were at least sixfold (P = 0.033) and fourfold (P = 0.091) higher, while the median fecal anti-CTB IgA response after two doses was estimated to be fourfold higher (P = 0.084) in the zinc-supplemented vaccinees. These observations show that zinc reduces the antitoxin and may enhance the antibacterial responses in serum. Zinc may also improve the intestinal antitoxin immune response. Oral zinc administration has the potential to modify critical immune responses to antigens applied to mucosal surfaces.

Laboratory monitoring in pediatric acute osteomyelitis and septic arthritis

The purpose of the current study was to determine the usefulness of erythrocyte sedimentation rate and C-reactive protein in pediatric bone and joint infections treated with and without surgery. The medical records of 50 patients admitted for acute osteomyelitis, septic arthritis, or both were reviewed retrospectively. There were 22 patients with septic arthritis, 20 with osteomyelitis, and eight with osteomyelitis with adjacent septic arthritis. There were 25 patients each in the surgical and nonsurgical groups. There was a statistically significant difference between the two groups regarding mean days to peak and normalization of erythrocyte sedimentation rate values and normalization of C-reactive protein values. Statistically significant differences were revealed for the mean days to normalization of erythrocyte sedimentation rate and C-reactive protein values among the patients with a diagnosis of osteomyelitis, septic arthritis, or both. The mean days to peak and normalization for erythrocyte sedimentation rate and C-reactive protein were twice as long in the surgical group as compared with the nonsurgical group. Complete recovery was achieved by all patients. This information should help the clinician in the diagnosis and treatment of children having surgery for acute osteomyelitis and septic arthritis.

Plasma total homocysteine levels and prognosis in patients with previous premature myocardial infarction: a 10-year follow-up study

OBJECTIVES

To explore plasma total homocysteine (tHcy) as a predictor of long-term prognosis after premature myocardial infarction (MI).

DESIGN

Prospective cohort study.

SETTINGS

Akershus University Hospital.

SUBJECTS

A total of 247 patients (193 men and 54 women) in stable clinical phase after premature MI (males: first MI at age < or =55; females < or =60).

MAIN OUTCOME MEASURES

The primary end-point was total mortality and the secondary end-point was cardiac death. The third end-point was major cardiac events: a combination of cardiac death, MI and cardiac arrest.

RESULTS

After 10 years, 44 patients had died, 36 from cardiac causes. Major cardiac event occurred in 70 patients. The relative risk for death of all causes increased 1.43 (95% CI, 1.08-1.88) per tHcy quartile (P for trend = 0.01), and was only modestly reduced after adjustment for age, ejection fraction, total cholesterol, C-reactive protein, fibrinogen, smoking and hypertension to 1.37 (95% CI, 1.04-1.80) (P for trend = 0.03). Similar results were observed when cardiac death was used as the end-point, but we observed no association between tHcy and the end-point major cardiac event.

CONCLUSIONS

Total homocysteine was an independent predictor of total and cardiac mortality in stable patients following premature MI. tHcy had no effect on major cardiac event in contrast to most other risk factors in this study. Thus, the mechanism(s) underlying the effects of homocysteine on coronary heart disease may differ from other risk factors.

Nitric oxide, atherosclerosis and the clinical relevance of endothelial dysfunction

The endothelium plays a key role in vascular homeostasis through the release of a variety of autocrine and paracrine substances, the best characterized being nitric oxide. A healthy endothelium acts to prevent atherosclerosis development and its complications through a complex and favorable effect on vasomotion, platelet and leukocyte adhesion and plaque stabilization. The assessment of endothelial function in humans has generally involved the description of vasomotor responses, but more widely includes physiological, biochemical and genetic markers that characterize the interaction of the endothelium with platelets, leukocytes and the coagulation system. Stable markers of inflammation such as high sensitivity C-reactive protein are indirect and potentially useful measures of endothelial function for example. Attenuation of the effect of nitric oxide accounts for the majority of what is described as endothelial dysfunction. This occurs in response to atherosclerosis or its risk factors. Much remains to be learned about the molecular and genetic pathophysiological mechanisms of endothelial cell abnormalities. However, pharmacological intervention with a growing list of medications can favorably modify endothelial function, paralleling beneficial effects on cardiovascular morbidity and mortality. In addition, several small studies have provided tantalizing evidence that measures of endothelial health might provide prognostic information about an individual patient's risk of subsequent events. As such, the sum of this evidence makes the clinical assessment of endothelial function an attractive surrogate marker of atherosclerosis disease activity. The review will focus on the role of nitric oxide in atherosclerosis and the clinical relevance of these findings.

High oxidized LDL and elevated plasma homocysteine contribute to the early reduction of myocardial flow reserve in healthy adults

BACKGROUND

Impairment of coronary blood flow reserve has been shown to be an early manifestation of atherosclerosis and coronary artery disease (CAD). We studied more closely the contribution of various risk factors on early deterioration of coronary function.

MATERIALS AND METHODS

Fifty-one young, apparently healthy adults, with normal or mildly elevated serum cholesterol levels but without other major risk factors for CAD, such as diabetes or hypertension, underwent positron emission tomography (PET) studies. Coronary flow reserve (CFR) was measured using O15-water. In addition to the classical risk factors, the role of several new risk indicators, such as low-density lipoprotein (LDL) oxidation, infection (Chlamydia pneumoniae antibodies), and inflammation parameters (adhesion molecules, ICAM, VCAM, selectin, and C-reactive protein), homocysteine and body iron stores were investigated.

RESULTS

Elevated lipid and lipoprotein levels were not associated with reduced coronary reactivity. However, high autoantibody titers against oxidized LDL (oxLDL) were associated with 21% lower CFR than low oxLDL (P < 0.05). Furthermore, high homocysteine levels predicted low CFR (P < 0.05). The other measured parameters, Chlamydia pneumoniae antibody levels, C-reactive protein and adhesion molecule concentrations did not associate with myocardial blood flow. In a stepwise regression model, oxLDL (P = 0.03), homocysteine (P = 0.04) and triglycerides (P = 0.018) were significant predictors of CFR.

CONCLUSIONS

The present study suggests an important role for oxidized LDL and plasma homocysteine on early impairment of coronary reactivity in young adults.

Elevated serum C-reactive protein levels and early arterial changes in healthy children

OBJECTIVE

Elevated serum concentration of C-reactive protein (CRP) predicts cardiovascular events in adults. Because atherosclerosis begins in childhood, we undertook a study to determine whether changes in brachial artery endothelial function and the thickness of the carotid intima-media complex, 2 markers of early atherosclerosis, are related to CRP levels in healthy children.

METHODS AND RESULTS

Brachial artery flow-mediated dilatation (FMD) and carotid artery intima-media thickness (IMT) were measured with ultrasound in 79 children (aged 10.5+/-1.1 years). Compared with the children with CRP levels under the detection limit (<0.1 mg/L, n=40, group 1), the children with higher CRP (0.1 mg/L< or =CRP< or =0.7 mg/L, n=20, group 2; CRP >0.7 mg/L, n=19, group 3) had lower FMD (9.0+/-4.4% versus 7.8+/-3.3% versus 6.5+/-2.6%, respectively; P=0.015 for trend) and greater carotid IMT (0.45+/-0.03 versus 0.46+/-0.04 versus 0.49+/-0.06 mm, respectively, P=0.002 for trend). CRP level remained a statistically significant independent predictor for brachial FMD and carotid IMT in multivariate analyses.

CONCLUSIONS

These data suggest that CRP affects the arteries of healthy children by disturbing endothelial function and promoting intima-media thickening. The findings support the hypothesis that CRP plays a role in the pathogenesis of early atherosclerosis.

C-reactive protein predicts death in patients with previous premature myocardial infarction--a 10 year follow-up study

Atherosclerosis is an inflammatory disease. C-reactive protein (CRP), a marker of inflammation, is associated with coronary heart disease (CHD). We measured CRP in a cohort of 247 patients (193 males and 54 females) who had had their first myocardial infarction (MI) at age < or = 55 (males) or < or = 60 (females). The cut-off values of the 25th, 50th and 75th centiles of CRP were 1.20, 2.37 and 4.20 mg/l. After 10 years, a total of 44 patients (17.8%) had died, 36 (81.8%) of cardiac causes. Unadjusted and adjusted (i.e. for age, ejection fraction (EF), serum total cholesterol (TC), fibrinogen, smoking and hypertension) relative risks (RRs) for total and cardiac mortality were generated. CRP was a strong predictor of death of all causes due to its strength as predictor of cardiac death. The RR of cardiac death was doubled with increasing CRP quartiles, and patients in the top quartile had six times as high risk of cardiac death as patients in the lowest quartile. The RRs were moderately attenuated after adjustment, but still significant. We conclude that CRP is a strong predictor of mortality in patients with premature MI. Thus, inflammation appears to be a critical prognostic factor in patients with previous premature MI.

Plasma N-terminal pro-atrial natriuretic peptide predicts death after premature myocardial infarction, but not as well as radionuclide ejection fraction. A ten-year follow-up study

OBJECTIVE

To assess N-terminal pro-atrial peptide (N-ANP) as a predictor of total and cardiac death in patients with previous premature myocardial infarction (MI).

DESIGN

In this prospective cohort study, we measured plasma N-ANP by ELIZA assays and ejection fraction (EF) by radionuclide ventriculography in a cohort of 247 patients (193 men and 54 women) who had had MI at a relatively young age (males: first MI at age < or =55; females <60).

RESULTS

After 10 years 44 patients had died, 36 from cardiac causes. After using a stepwise procedure to adjust for other prognostic factors (i.e. plasma total homocysteine (tHcy), C-reactive protein and age), the relative risk (RR) was 2.00 (95% confidence interval (CI) 1.05-3.80) (p = 0.03) for death of all causes and 2.32 (95% CI 1.19-4.55) (p=0.01) for cardiac death when the top quartile was compared to the three lower quartiles of N-ANP. When radionuclide EF entered the Cox model, N-ANP became insignificant as a predictor of mortality.

CONCLUSION

N-ANP was a significant predictor of total death and cardiac death in young survivors of MI, but radionuclide EF was a more independent prognostic variable.

High sensitivity immunoassays for C-reactive protein: promises and pitfalls

C-reactive protein (CRP) has historically been measured in the clinical laboratory for the detection and monitoring of occult infection and inflammation, using immunoturbidimetric or immunonephelometric techniques. The recent commercial availability of automated high-sensitivity assays has enabled investigators to measure CRP at levels previously unattainable on a routine basis and to explore its clinical utility in apparently healthy individuals. CRP concentrations increased above the individuals' baselines but still within the normal reference intervals have been observed in association with increasing age, obesity, and smoking and in individuals with chronic infections such as Chlamydia pneumoniae and Helicobacter pylori. More importantly, however, data from prospective studies have shown CRP to be a strong and independent predictor of future coronary events in subjects with and without coronary heart disease. An algorithm for risk assessment of coronary risk employing both CRP and lipid concentrations has recently been proposed. However, in order for this approach to be incorporated into clinical practice, agreement among the various CRP methods must be achieved. Of critical importance to this process is a basic understanding of issues affecting assay performance. Factors such as assay precision, sensitivity, matrix effects, calibration, and standardization need to be addressed adequately by the in vitro diagnostic industry and the clinical laboratory.

C-Reactive Protein Concentrations and Angiographic Characteristics of Coronary Lesions

Background: C-Reactive protein (CRP) is a strong predictor of clinical outcome in coronary artery disease (CAD), and inflammation has been implicated in the process. We aimed to evaluate whether CRP concentrations measured with a new, automated particle-enhanced immunoturbidimetric method for high-sensitivity CRP may be related to specific high-risk angiographic features of coronary lesions.

Methods: In a cross-sectional study, we examined 103 consecutive patients undergoing cardiac catheterization for suspected CAD. We assessed the association of preprocedural CRP concentrations with clinical presentation (unstable angina) and angiographic features of coronary lesions.

Results: Twenty patients had unstable angina. Independent predictors of unstable angina included increased CRP [odds ratio (OR), 2.93 per 10-fold increase in CRP; 95% confidence interval (CI), 1.28–6.69; P = 0.01] and the presence of macroscopic thrombus (OR, 7.08; 95% CI, 1.33–37.8; P = 0.02). Thirty-two culprit lesions had macroscopic thrombus or eccentric/irregular discrete morphology without total occlusion. Increased CRP was the strongest predictor of such features (OR, 2.04 per 10-fold increase in CRP; 95% CI, 1.03–4.04; P = 0.04), and the effect was independent of the presence of unstable angina.

Conclusions: Among patients with suspected CAD undergoing coronary angiography, increased CRP is strongly associated with unstable angina and with specific high-risk features of the culprit coronary lesions.

C-reactive protein is not associated with the presence or extent of calcified subclinical atherosclerosis

BACKGROUND

Both high-sensitivity C-reactive protein (hsCRP) and electron beam computed tomography (EBCT) coronary artery calcification (CAC) are valid markers of cardiovascular risk. It is unknown whether hsCRP is a marker of atherosclerotic burden or whether it reflects a process (eg, inflammatory fibrous cap degradation) leading to acute coronary events.

METHODS

A nested case-control study was performed of 188 men enrolled in the Prospective Army Coronary Calcium study. The serum hsCRP levels (latex agglutination assay) were evaluated in subjects with CAC (CAC score >0, n = 94) and compared with age- and smoking status-matched control subjects (CAC score 0, n = 94).

RESULTS

Levels of hsCRP in the highest quartile were related to the following coronary risk factors: smoking status, low-density lipoprotein cholesterol, body mass index, glycosylated hemoglobin, fibrinogen, and homocysteine. The mean hsCRP level was similar in cases (+CAC, 0.20 +/- 0.22 mg/dL) and controls (-CAC, 0.19 +/- 0.21 mg/dL; P =.81) and was unrelated to the log-transformed CAC score (r < 0.01, P =.91). Multivariable analysis controlling for standard risk factors, aspirin, and statin therapy found only that low-density lipoprotein cholesterol was related to CAC.

CONCLUSIONS

Despite associations with standard and emerging cardiovascular risk factors, hsCRP is unrelated to the presence and extent of calcified subclinical atherosclerosis. This implies that CAC (a disease marker) and hsCRP (a process marker) may be complementary for the prediction of cardiovascular risk.

MicroCRP: a highly sensitive CRP method applied in the monitoring of renal allograft recipients

A new ultrasensitive fluoroimmunometric assay for C-reactive protein (CRP), called MicroCRP assay, has a lower detection limit of 0.05 mg/l, and a CV of 7.6% at concentration 0.25 mg/l. The microCRP levels in healthy adults show a skewed distribution, median 0.90 mg/l and mean 1.4 mg/l, with 2.5th and 97.5th percentiles of 0.17 and 4.7 mg/l, respectively, and no gender-related or age differences. Serial microCRP was applied in the monitoring of 37 renal allograft recipients. The operative trauma gave rise to an initial CRP peak, usually on day 2 after transplantation, with a return to preoperative value 1 week after surgery. There were significant CRP elevations (>25%) in all cases of rejections, indicating 100% sensitivity. The microCRP values started to increase about 3 days (range -1 to 9 days) before the rise in creatinine. The microCRP peak tended to be higher in rejection episodes with a vascular component, compared with episodes of cellular rejection (p=0.05). A rise in microCRP at days 7-12 after transplantation seems to predict the risk of rejections later on, and probably reflects the primary immune response to the graft. Recipients without this primary CRP response (only 6 of 37 patients) subsequently had uncomplicated courses. Tracking of values below the traditional lower limit is essential in order to recognize the different CRP peaks. Serial monitoring of microCRP is well suited for clinical use and provides clinical information previously unattainable with other assay systems.