Relationship between CRP and clinical course of unstable angina depends on assay method

BACKGROUND

The CRP concentration has been identified as a cardiovascular risk factor in healthy volunteers and in patients with stable and unstable angina pectoris. There is little information about the comparability of the results of different CRP assays and it has also not been evaluated whether different assays give different associations with risk.

METHODS

We studied this in the APRAIS study, a study on 211 patients with unstable angina pectoris who were admitted to hospital and in whom we studied the association between the CRP concentration on admission and the in-hospital clinical course (refractiviness to medication). We used two different immunological methods: an in-house ELISA using polyclonal rabbit anti-human CRP antibodies as catching and tagging antibody and a commercial nephelometric method (Dade-Behring).

RESULTS

The analytical variation was much smaller for the nephelometric method than for the in-house ELISA. Both methods gave higher levels in the refractory group than in the stabilized group, but only for the nephelometric method was this difference significant. Also, when the relative risk is calculated, it is clear that the more accurate nephelometric method can better discriminate between the two groups [RR 2.19 (95% CI 0.94-5.11) for the nephelometric method and RR 1.30 (95% CI 0.56-3.03) for the ELISA].

CONCLUSIONS

In conclusion, the nephelometric method measures the CRP concentration with a smaller intra- and interassay variation. The nephelometric method can also better discriminate between unstable angina patients who will be stabilized and those who are refractory during hospitalization.

The association between inflammation markers, coronary artery disease and smoking

Inflammation and smoking are associated with risk of cardiovascular disease, but not much is known yet about their relationship. We studied in 15 smoking and 15 nonsmoking patients with coronary artery disease (CAD) and in 15 smoking and 15 nonsmoking healthy subjects the relationships with the inflammatory markers C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha). IL-6 and TNF-alpha were significantly higher in patients than in controls, both in smokers and in nonsmokers. Smoking only had a significant effect on IL-6, and mainly in the controls. In conclusion, inflammation is affected by both smoking and cardiovascular disease.

Genetic polymorphisms modify the response of factor VII to oral contraceptive use: an example of gene-environment interaction

Elevated plasma levels of factor VII and fibrinogen are risk factors for cardiovascular disease, especially arterial thrombosis. Oral contraceptive use increases factor VII and fibrinogen plasma levels. It has been described that DNA polymorphisms are associated with the plasma levels of hemostatic variables and their regulation. The R/Q353 polymorphism in the factor VII gene and the -455G/A polymorphism in the fibrinogen beta-gene are associated with plasma levels of factor VII and fibrinogen, respectively. We analysed data of a randomised study (n = 95) in which two types of oral contraceptives were compared with regard to their effect on factor VII and fibrinogen, in which we also determined R/Q353 and -455G/A polymorphisms. Women were allocated randomly to either receiving a monophasic oral contraceptive containing 75 micrograms of gestodene and 20 micrograms of ethinyl estradiol, or 150 micrograms of desogestrel and 20 micrograms of ethinyl estradiol. Blood was taken before treatment and after 3 and 6 months of oral contraceptive use. Factor VII and fibrinogen increased significantly after 3 and 6 months of oral contraceptive use; the increase in factor VII was higher in the desogestrel group than in the gestodene group at 3 and 6 months. For fibrinogen, there were no intergroup differences at 3 and 6 months. At baseline, an association between genotype and plasma factor VII and fibrinogen levels was observed. In multivariate analysis, the R/Q353 polymorphism and the type of oral contraceptive were determinants of the effect on the change in factor VII, with the highest increase in women carrying the Q allele and using the desogestrel-containing oral contraceptive, and the lowest increase in women with the RR genotype who use the gestodene-containing oral contraceptive. For fibrinogen, no interaction among type of oral contraceptive, -455G/A polymorphism, and change in plasma levels was observed. We conclude that an individual's genetic variation may contribute to the response of plasma factor VII to oral contraceptive use.

Long-term analytical performance of hemostasis field methods as assessed by evaluation of the results of an external quality assessment program for antithrombin

BACKGROUND

It is important for a laboratory to know the stability of performance of laboratory tests over time. The aim of this study was to adapt from the field of clinical chemistry a method to assess the long-term analytical performance of hemostasis field methods.

METHODS

The linear regression model was used to compare the laboratory results with the consensus mean value of a survey. This model was applied to plasma antithrombin activity using the data for 82 laboratories, collected between 1996 and 1999 in the European Concerted Action on Thrombosis (ECAT) external quality assessment program. The long-term total, random, and systematic error were calculated. The variables introduced to define the long-term performance in this model were the long-term analytical CV (LCV(a)) and the analytical critical difference (ACD), which indicates the minimum difference necessary between two samples measured on a long-term time-scale to consider them statistically significantly different.

RESULTS

The systematic error (bias) ranged from 4.5 to 103 units/L. The random error ranged from 24.4 to 242 units/L. For the majority of the laboratories, random error was the main component (>75%) of the total error. The LCV(a), after adjustment for the contribution of the bias, ranged from 2.8% to 48%. The ACD ranged from 78 to 1290 units/L with a median value of 190 units/L. No statistically significant differences were observed for either LCV(a) or ACD between the two different measurement principles for antithrombin activity based on the inhibition of either thrombin or factor Xa.

CONCLUSIONS

This linear regression model is useful for assessing the total error, random error, and bias for hemostasis field methods. The LCV(a) and ACD for measurement on a long-term time-scale appear to be useful for assessing the long-term analytical performance.

Inflammatory mediators and cell adhesion molecules as indicators of severity of atherosclerosis: the Rotterdam Study

Inflammatory mediators and soluble cell adhesion molecules predict cardiovascular events. It is not clear whether they reflect the severity of underlying atherosclerotic disease. Within the Rotterdam Study, we investigated the associations of C-reactive protein (CRP), interleukin-6 (IL-6), soluble intercellular adhesion molecule-1, and soluble vascular cell adhesion molecule-1 with noninvasive measures of atherosclerosis. Levels of CRP were assessed in a random sample of 1317 participants, and levels of IL-6 and soluble cell adhesion molecules were assessed in a subsample of 714 participants. In multivariate analyses, logarithmically transformed CRP (regression coefficient [beta]=-0.023, 95% CI -0.033 to -0.012) and IL-6 (beta=-0.025, 95% CI -0.049 to -0.001) were inversely associated with the ankle-arm index. Only CRP was associated with carotid intima-media thickness (beta=0.018, 95% CI 0.010 to 0.027). Compared with the lowest tertile, the odds ratio for moderate to severe carotid plaques associated with levels of CRP in the highest tertile was 2.0 (95% CI 1.3 to 3.0). Soluble intercellular adhesion molecule-1 levels were strongly associated with carotid plaques (odds ratio 2.5, 95% CI 1.5 to 4.4 [highest versus lowest tertile]). Soluble vascular cell adhesion molecule-1 was not significantly associated with any of the measures of atherosclerosis. This study indicates that CRP is associated with the severity of atherosclerosis measured at various sites. Associations of the other markers with atherosclerosis were less consistent.

Internal quality control of PCR-based genotyping methods in research studies and patient diagnostics

Genetic analyses are increasingly integrated in the clinical laboratory, and internal quality control programmes are needed. We have focused on quality control aspects of selected polymorphism analyses used in thrombosis research. DNA was isolated from EDTA-blood (n = 500) by ammonium acetate precipitation and analysed for 18 polymorphisms by polymerase chain reaction (PCR), i. e. restriction fragment length polymorphisms, allele specific amplification, or amplification of insertion/deletion fragments. We evaluated the following aspects in the analytical procedures: sample handling and DNA-isolation (pre-analytical factors), DNA-amplification, digestion with restriction enzymes, electrophoresis (analytical factors), result reading and entry into a database (post-analytical factors). Furthermore, we evaluated a procedure for result confirmation. Isolated DNA was of good quality (42 microg/ml blood, A260/A280 ratio >1.75, negative DNAsis tests), and the reagent blank was contaminated in <1% of the results. Occasionally, results were re-analysed because of positive reagent blanks (< 1%) or because of problems with the controls (<5%). On confirmation, we observed 4 genotyping discrepancies. Control of data handling revealed 0.1% reading mistakes and 0.5% entry mistakes. Based on our experiences we propose an internal quality control programme for widely used PCR-based haemostasis polymorphism analyses.

A case-only approach for assessing gene by sex interaction in human longevity

As one aspect of the complex feature of longevity, gene by sex interaction plays an important role in influencing human life span. With advances in molecular genetics, more studies aimed at assessing gene by sex interaction are expected. New and valid statistical methods are needed. In this article, we introduce a nontraditional approach, the case-only design, which was originally proposed for assessing gene and disease associations, to detect gene by sex interaction in human longevity. Applications of this method to data collected from centenarian studies show that it can produce consistent results as compared with results obtained from case-control and other approaches. The method cannot be used as a substitute for traditional case-control studies since it is limited to the detection of interactions only. However, the easily applicable case-only approach can be an important tool for screening many potential genes that contribute to human longevity.

Effects of Gemfibrozil and Ciprofibrate on Plasma Levels of Tissue-type Plasminogen Activator, Plasminogen Activator Inhibitor-1 and Fibrinogen in Hyperlipidaemic Patients

Evaluation of fibrate treatment in humans has focused primarily on its anti-lipidaemic effects. A potentially favourable haemostasis-modulating activity of fibrates has also been recognized but the data are not consistent. We sought to learn more about this variability by examining the effects of gemfibrozil and ciprofibrate on plasma levels of tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and fibrinogen in primary hyperlipidaemic patients after six and twelve weeks of treatment using different assay systems for PAI-1 and fibrinogen. Although both fibrates effectively lowered triglyceride and cholesterol levels, no effect on the elevated baseline antigen levels of t-PA and PAI-1 was observed after fibrate treatment. However, both fibrates influenced plasma fibrinogen levels, albeit in a different way. Fibrinogen antigen levels were elevated by 17.6% (p <0.05) and 24.3% (p <0.001) with gemfibrozil after six and twelve weeks, respectively, whereas with ciprofibrate there was no effect. Using a Clauss functional assay with either a mechanical end point or a turbidity-based end point, no significant change in fibrinogen levels was seen after six weeks of gemfibrozil treatment. However, after twelve weeks, gemfibrozil enhanced functional fibrinogen levels by 7.2% (p <0.05) as assessed by the Clauss mechanical assay, but decreased functional fibrinogen levels by 12.5% (p <0.0001) when a Clauss assay based on turbidity was used. After six or twelve weeks of ciprofibrate treatment, functional fibrinogen levels were decreased by 10.1% (p <0.001) and 10.5% (p <0.0001), respectively on the basis of Clauss mechanical and by 14.2% (p <0.001) and 28.2% (p <0.0001), respectively with the Clauss turbidimetric assay. A remarkable and consistent finding with both fibrates was the decrease in functionality of fibrinogen as assessed by the ratio of functional fibrinogen (determined by either of the two Clauss assays) to fibrinogen antigen.

Taken together, our results indicate that at least part of the variability in the effects of fibrates on haemostatic parameters can be explained by intrinsic differences between various fibrates, by differences in treatment period and/or by the different outcomes of various assay systems. Interestingly, the two fibrates tested both reduced the functionality of fibrinogen.