Standardization of High-Sensitivity Immunoassays for Measurement of C-Reactive Protein; II: Two Approaches for Assessing Commutability of a Reference Material

Recent AHA/ACC guidelines on cholesterol management expands the role of the clinical laboratory

The American Heart Association (AHA) and American College of Cardiology (ACC) recently published new guidelines for managing blood cholesterol. Five years from the publication of Pooled Cohort Equation to estimate 10-year risk of atherosclerotic cardiovascular disease (ASCVD), the newest guidelines put more focus on individualized risk assessment which necessitates increased participation of laboratory medicine in the prevention and management of ASCVD. This mini-review summarizes key ideas from the new guideline that influence laboratory practice, including the renewed low-density lipoprotein cholesterol (LDL-C) treatment targets in primary and secondary prevention, the use of non-fasting lipids, new calculations of LDL cholesterol, and recommendations on assessing risk-enhancing factors in certain populations to aid the decision on statin and non-statin therapy. The shift in strategies for monitoring and lowering LDL-C has created opportunities for clinical laboratorians to more actively contribute to better identification of individuals at risk for ASCVD and partner with physicians taking care of the patient.

Replication and reproducibility issues in the relationship between C-reactive protein and depression: A systematic review and focused meta-analysis

One of the most common inflammatory markers examined in depression is C-reactive protein (CRP). However, the magnitude of the association between CRP and depression when controlling for potentially confounding factors such as age, sex, socio-economic status, body mass index, medication and other substance use, and medical illness, is unclear. Inconsistencies in other methodological practices, such as sample collection, assaying, and data cleaning and transformation, may contribute to variations in results. We aggregate studies that examined the association between CRP and depression in two ways. First, a systematic review summarizes how studies of CRP and depression have reported on methodological issues. Second, a tiered meta-analysis aggregates studies that have adhered to various levels of methodological rigor. Findings from the systematic review indicate a lack of protocol detail provided. The effect between depression and CRP was small, but highly significant across all stages of the meta-analysis (p < 0.01). The effect size in the most methodologically rigorous stage of the meta-analysis, which included studies controlling for age, sex, obesity, medical conditions and substance, medication, or psychosocial factors, was small (r = 0.05). There were also only 26 articles in this stage (13% of studies from the systematic review), suggesting that more studies that consistently account for these confounding factors are needed. Additionally, an a priori quality score of methodological rigor was a significant moderator in this stage of the meta-analysis. The effect size was strikingly attenuated (r = 0.005) and non-significant in studies with higher quality scores. We describe a set of recommended guidelines for future research to consider, including sample collection and assaying procedures, data cleaning and statistical methods, and control variables to assess.

Comparison of results from commercial assays for plasma CTX: The need for harmonization

INTRODUCTION

Plasma C-terminal telopeptide of type I collagen (CTX) is the nominated reference bone resorption marker. We set out to test the agreement of patients' results between the available plasma CTX assays.

METHODS

Samples were collected from patients attending tertiary hospitals and clinics for investigation and management of metabolic bone disease. Plasma (EDTA) samples were collected from fasted patients between 7.00 am and 11.00 am, divided into three portions and stored at -20°C until analysis. Plasma CTX was measured by enzyme-linked immunosorbent assay (ELISA) (Immunodiagnostic Systems plc), E170 (Roche Diagnostics) and IDS-iSYS (Immunodiagnostic Systems plc) methods. Agreement of patient sample results was assessed by Passing and Bablok regression. Commutability of the calibrators in each kit was assessed by assaying each calibrator in the alternate methods and comparing the observed results with those expected based on the relevant patients' samples method comparison; ±8.1% was set as the criterion for commutablity.

RESULTS

161 specimens were analysed. Regression parameters (slope, intercept) were 0.788, 0.2 ng/L for Roche vs ELISA, 1.266 and -109 ng/L for iSYS vs ELISA and 1.605 and -109 ng/L for iSYS vs Roche. Only the ELISA calibrator assayed in the Roche assay gave a result within 8.1% of the expected value.

CONCLUSIONS

There is significant disagreement between the results generated for patient samples by the 3 CTX assays and limited commutability of the currently supplied calibrator materials between assays. Harmonization of the results from the different assays would greatly enhance the value of CTX as the reference bone resorption marker.

TNF-α depuration is a predictor of mortality in critically ill patients under continuous veno-venous hemodiafiltration treatment

INTRODUCTION

Critically ill patients with acute kidney injury (AKI) present high mortality rates. The magnitude of inflammatory response could determine the prognosis of such patients. Continuous renal replacement therapy (CRRT) may play an important role in removing inflammatory mediators in patients with AKI.

AIM

To investigate whether the magnitude of inflammatory mediator's removal is associated with mortality among critically ill patients on CVVHDF, a CRRT modality.

METHODS

This study consisted of 64 critically ill patients requiring CVVHDF. Plasma levels of C3a, TNF-α, IL-10, IL-6, IL-1β, sTNFRI and sTNFRII were determined by enzyme-linked immunosorbent assay (ELISA) at the beginning of CVVHDF and after 24h (outlet). Clearance of cytokines during the first 24h of CVVHDF was calculated. Clinical and laboratory data were acquired from patient's records data.

RESULTS

Mean age of patients requiring CVVHDF was 63years, 67.2% were men and 87.3% were Caucasian. Thirty-five (35) patients (54.7%) died. Comparing non-survivors with the group of survivors we observed higher incidence of sepsis (68.6 versus 37.9%, p<0.05), higher APACHE II score (34.8±7.6 versus 29.2±7.1, p<0.05) and higher lactate levels (23.2±17.6 versus 16.4±6.6, p<0.05). According to the inter-tertile range of TNF-α clearance (ITR1 (<0.54); ITR2 (0.54-2.93); ITR3 (>2.93)) we found that those patients with higher TNF-α removal by RRT (ITR3) had a better survival. Multivariable analysis showed that lower clearance of TNF-α remained independently associated with high mortality after adjustment for sex, age, use of vasoactive drugs, APACHE II score sepsis, creatinine and lactate before CVVHDF (HR: 0.179, 95% IC: 0.049-0.661, p<0.01).

CONCLUSION

The attenuation of inflammatory response may be related to the lower mortality observed on those patients with higher TNF-α removal by CVVHDF.

Epidemiological evidence against a role for C-reactive protein causing leptin resistance

OBJECTIVE

It has been suggested that elevated levels of C-reactive protein (CRP) might interfere with leptin signalling and contribute to leptin resistance. Our aim was to assess whether plasma levels of CRP influence leptin resistance in humans, and our hypothesis was that CRP levels would modify the cross-sectional relationships between leptin and measures of adiposity.

DESIGN AND METHODS

W assessed four measures of adiposity: BMI, waist circumference, fat mass and body fat (%) in 2113 British Regional Heart Study (BRHS) men (mean (s.d.) age 69 (5) years), with replication in 760 (age 69 (6) years) European Male Ageing Study (EMAS) subjects.

RESULTS

IN BRHS subjects, leptin correlated with CRP (SPEARMAN'S R=0.22, P0.0001). Leptin and crp correlated with all four measures of adiposity (R VALUE RANGE: 0.22-0.57, all P<0.0001). Age-adjusted mean levels for adiposity measures increased in relation to leptin levels, but CRP level did not consistently influence the β-coefficients of the regression lines in a CRP-stratified analysis. In BRHS subjects, the BMI vs leptin relationship demonstrated a weak statistical interaction with CRP (P=0.04). We observed no similar interaction in EMAS subjects and no significant interactions with other measures of adiposity in BRHS or EMAS cohorts.

CONCLUSION

We have shown that plasma CRP has little influence on the relationship between measures of adiposity and serum leptin levels in these middle-aged and elderly male European cohorts. This study provides epidemiological evidence against CRP having a significant role in causing leptin resistance.

Standardization of measurements of 25-hydroxyvitamin D3 and D2

The vitamin D status is increasingly assessed/monitored in different populations, research cohorts and individual patients. This is done by measuring the liver metabolites 25-hydroxyvitamin D3 and D2 as biomarkers. Recommendations for using specific serum concentrations of these biomarkers to assess a person's vitamin D status were done. This requires current vitamin D assays to be sufficiently accurate over time, location and laboratory procedures. In view of the fact that several studies demonstrated that current 25(OH)D measurement methods do not meet this prerequisite, standardization is needed. This paper rehearses the basic concept of standardization, in particular applied to measurements of 25-hydroxyvitamin D. Progress has been made by establishing a reference measurement system consisting of reference methods and reference materials. Coordinated efforts to improve the accuracy and standardize measurements are being performed by organizations such as the U.S. NIH, the CDC and Prevention, the NIST together with their national and international partners. Beyond describing the available reference measurement system and its use as calibration hierarchy to establish traceability of measurements with routine laboratory methods to the SI-unit, this report will also focus on other aspects considered essential for a successful and sustainable standardization, such as analytical issues related to the definition of the measurand and analytical performance goals.

Effects of simvastatin on cytokines secretion from mononuclear cells from critically ill patients with acute kidney injury

PURPOSE

To assess the in vitro effects of simvastatin on IL-10 and TNF-α secretion from peripheral blood mononuclear cells (PBMC) of critically ill patients with and without acute kidney injury (AKI).

METHODS

PBMC were collected from 63 patients admitted to the intensive care unit (ICU) and from 20 healthy controls. Patients were divided in 3 subgroups: with AKI, with sepsis and without AKI and with AKI and sepsis. After isolation by ficoll-gradient centrifugation cells were incubated in vitro with LPS 1 ng/mL, simvastatin (10(-8)M) and with LPS plus simvastatin for 24h. TNF-α and IL-10 concentrations on cells surnatant were determined by ELISA.

RESULTS

Cells isolated from critically ill patients showed a decreased spontaneous production of TNF-α and IL-10 compared to healthy controls (6.7 (0.2-12) vs 103 (64-257) pg/mL and (20 (13-58) vs 315 (105-510) pg/mL, respectively, p<0.05). Under LPS-stimulus, IL-10 production remains lower in patients compared to healthy control (451 (176-850) vs 1150 (874-1521) pg/mL, p<0.05) but TNF-α production was higher (641 (609-841) vs 406 (201-841) pg/mL, p<0.05). The simultaneous incubation with LPS and simvastatin caused decreased IL-10 production in cells from patients compared to control (337 (135-626) vs 540 (345-871) pg/mL, p<0.05) and increased TNF-α release (711 (619-832) vs 324 (155-355) pg/mL, p<0.05). Comparison between subgroups showed that the results observed in TNF-α and IL-10 production by PBMC from critically ill patients was independent of AKI occurrence.

CONCLUSIONS

The PBMC treatment with simvastatin resulted in attenuation on pro-inflammatory cytokine spontaneous production that was no longer observed when these cells were submitted to a second inflammatory stimulus. Our study shows an imbalance between pro and anti-inflammatory cytokine production in PBMC from critically ill patients regardless the presence of AKI.

C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) as inflammation markers in elderly patients with stable chronic obstructive pulmonary disease (COPD)

Erythrocyte sedimentation rate (ESR) might represent a less expensive alternative to C-reactive protein (CRP) as a marker of systemic inflammation in stable chronic obstructive pulmonary disease (COPD). We tried to verify this hypothesis in 223 consecutive outpatients aged 65 years or more with stable COPD enrolled in a multicenter observational study. Patients were grouped according to normal/increased ESR/CRP values and groups were compared with regard to clinical and laboratory characteristics. Correlations between CRP, ESR and selected variables of interest were assessed by Spearman's ζ-test and multivariate linear regression analysis. CRP was weakly and inversely correlated with the forced expiratory volume in the first second (FEV1%) (Spearman's ζ = -0.15; p < 0.027), while ESR was not (Spearman's ζ = -0.05; p = 0.411). The highest prevalence of anemia and hypoalbuminemia and the lowest FEV1% were recorded in high ESR-high CRP group. For anemia B = 14.180 ± 3.521 (± S.E.M.); p = 0.001 and hypoalbuminemia B = 10.241 ± 3.790; p = 0.007 qualified as significant independent correlates of ESR values, while only FEV1 remained significantly associated with CRP values (B = -0.570 ± 0.258; p = 0.028). In conclusion, CRP, but not ESR, shows a weak correlation with COPD severity, while anemia and hypoalbuminemia are main correlates of high ESR. Neither ESR, nor CRP qualify as reliable markers of COPD severity and seem to reflect the effects of different determinants.

Analysis of the Physicochemical State of C-Reactive Protein in Different Preparations Including 2 Certified Reference Materials

BACKGROUND

Standardization of clinical measurements of C-reactive protein (CRP) is based on the availability of reference materials. The serum protein reference material ERM-DA470 was used as a calibrant for various commercially available immunoassays but has now been exhausted. The recently released ERM-DA470k/IFCC was intended to fully replace ERM-DA470. However, the new material was not suited for the certification of CRP because of a bias introduced by the lyophilization process that caused loss of about 20% of CRP measurable by routine immunoassays, compared with the nonlyophilized material that was stored in a liquid frozen state.

METHODS

We investigated the physicochemical state of CRP in a set of 4 lyophilized and 2 nonlyophilized serum-based CRP-containing materials by semi-native gel electrophoresis, Western blotting, and gel filtration.

RESULTS

We detected a monomeric form of CRP (mCRP) in lyophilized materials at a concentration significantly higher than seen in the materials not subjected to lyophilization. Different reconstitution protocols led to variations of the monomeric CRP fraction found in reconstituted, previously lyophilized material.

CONCLUSIONS

Most of the 20% loss in measured CRP after lyophilization of the material can be accounted for by the dissociation of natively pentameric CRP into subunits. The observed dissociation results from lyophilization and subsequent reconstitution of the material at insufficient concentration levels of calcium ions. In the presence of various protein forms, differences in antibody specificity and reactivity between immunoassays and alterations of stoichiometry of antigen–antibody interactions can contribute to the divergence of the measured values.

Standardization of ceruloplasmin measurements is still an issue despite the availability of a common reference material

The purpose of measurement standardization is to achieve closer comparability of results obtained using different commercial systems. Regarding serum protein immunoassays, a reference preparation (BCR-470) was released in 1993 and adopted by manufacturers across the world to value-assign their assay calibrators for routine methods to reduce method-dependent variation. Moving from nephelometric (Beckman Immage 800) to turbidimetric determination (Roche Cobas c 501) of seven serum proteins, we preliminarily checked the comparability of results between the two systems. The study was performed according to the CLSI EP9-A protocol on 30 fresh sera, tested on each system in duplicate, and subdivided on two different days, without recalibration and using manufacturers' control materials to validate the runs. Both manufacturers' package inserts provide statements that kit calibrators are traceable to BCR-470. Suggested reference intervals are also the same. Although a fairly good correlation was observed (r = 0.955), the comparison of ceruloplasmin methods produced evidence of highly significant proportional (regression slope, 0.572) and constant bias (intercept, 0.05 g/L). Absolute and percentage mean differences were -0.11 g/L (95% confidence interval (CI) -0.13 to -0.10 g/L) and -39.1% (CI -43.1 to -35.2%), respectively. No other evaluated proteins showed similar problems. Lacking a ceruloplasmin reference method, it is impossible to demonstrate that one of the two assays produces true ceruloplasmin values. The problem is, however, that results coming from the two assays are clearly not comparable. This may be either due to a lack of commutability of the reference material with biological samples in the evaluated assays or to calibration problems by manufacturers in one of the stages of the calibration hierarchy.