Validation of rapid fecal calprotectin assay using particle enhanced turbidimetric immunoassay for inflammatory bowel disease

Fecal calprotectin (FC) is a promising biomarker for diagnosis and treatment of inflammatory bowel disease, ulcerative colitis (UC), and Crohn's disease. An enzyme immunoassay (EIA) is widely used for FC detection, though the considerable lag time, up to several days, causes clinical management delay. This study was performed to examine the new rapid kit fCAL-turbo, which is based on a particle-enhanced turbidimetric immunoassay (15 min), by comparing FC values with other EIAs (EliA, PhiCal, Bühlmann) and endoscopic scores. Using 94 samples, fCAL-turbo showed strong significant positive correlations with the other kits (Spearman's r = 0.9178-0.9886). Of 74 UC patients, 69 underwent an endoscopy and fCAL-turbo reflected endoscopic activity with a moderate correlation with Mayo endoscopic subscore (MES) (r = 0.6945, others r = 0.6682-0.7013). Receiver operating characteristic analyses based on MES 0 versus 1-3 showed a similar efficacy as compared to the other kits (cut-off and area under the curve: 89.70 µg/g and 0.8592, respectively, others 62.35-138.4 µg/g and 0.8280-0.8611, respectively). Furthermore, multiple regression analysis confirmed that fCAL-turbo results significantly contributed to prediction of MES 0 with a higher t-value as compared to the other biomarkers. fCAL-turbo showed strong correlations with the other kits and also demonstrated excellent performance for predicting endoscopic remission of UC.

Development and characterization of a latex turbidimetric immunoassay using rabbit anti-CRP single-chain Fv antibodies

In this study, we developed and demonstrated a latex turbidimetric immunoassay (LTIA) using latex beads immobilized with rabbit monoclonal single-chain variable fragments (scFvs) selected from an scFv-displayed phage library. Sixty-five different anti-c-reactive protein (anti-CRP) scFv clones were identified after biopanning selection using antigen-coupled multi-lamellar vesicles. By ranking antigen-binding clones using the apparent dissociation rate constant (appkoff) as a sorting index, scFv clones with a dissociation constant (KD free) ranging from 4.07 × 10-9 M to 1.21 × 10-11 M were isolated. Among them, three candidates (R2-6, R2-45, and R3-2) were produced in the culture supernatant at concentrations of 50 mg/L or higher in flask culture and maintained at considerably high antigen-binding activity in immobilized state on the CM5 sensor chip surface. All the scFv-immobilized latexes (scFv-Ltxs) prepared were well-dispersed in 50 mM MOPS at pH 7.0, without additives for dispersion, and their antigen-dependent aggregation was sufficiently detectable. The reactivity of scFv-Ltx to antigen differed among the scFv clones, in particular, R2-45 scFv-Ltx detected the CRP with the highest signal. Furthermore, the reactivity of scFv-Ltx varied significantly with salt concentration, scFv immobilization density, and the type of blocking protein. Particularly, antigen-dependent latex aggregation improved significantly in all rabbit scFv clones when scFv-Ltx was blocked with horse muscle myoglobin compared with conventional bovine serum albumin; while their baseline signals in the absence of antigen were fully stable. Under optimal conditions, R2-45 scFv-Ltx exhibited greater aggregation signals with antigen concentrations higher than those produced by conventional polyclonal antibody-immobilized latex for CRP detection in LTIA. The methodology for rabbit scFv isolation, immobilization, and antigen-dependent latex aggregation demonstrated in the present study can be applicable to scFv-based LTIA for various target antigens.

Falsely decreased vancomycin caused by rheumatoid factor: A case report

BACKGROUND

Vancomycin is associated with potential nephrotoxicity and trough concentrations need to be monitored in certain patients. Falsely decreased vancomycin measurement may result in overtreatment and need to be identified promptly by clinicians and pharmacists to avoid toxicities.

METHODS AND RESULTS

We report a case of rheumatoid factor-mediated falsely low vancomycin measurement with Abbott particle-enhanced turbidimetric inhibition immunoassay (PETINIA) method. Reanalyzing the sample using an alternative method, removing the interferences using heterophile blocking reagent as well as rheumatoid factor clean-up solution all helped to solve the false results. Results from alternative method and interference studies showed vancomycin concentrations reached toxic concentrations in the patient and administration of the drug was immediately terminated. The patient experienced a transient increase in serum creatinine.

CONCLUSIONS

Even though most modern immunoassays use blocking agents to neutralize interfering antibodies such as rheumatoid factor, it is important for health care professionals to understand that occasional interference still occurs due to the heterogeneous nature of rheumatoid factor.

Evaluation of Latex Immunoturbidimetric Assay Thresholds and HIT in Cardiothoracic Surgery

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a common differential diagnosis in cardiothoracic surgery. The latex immunoturbidimetric assay (LIA) is an enhanced immunoassay that has recently been introduced for the detection of total HIT immunoglobulin and retains a higher specificity of 95% compared to the enzyme-linked immunosorbent assay.

OBJECTIVES

To investigate if a semiquantitative relationship exists between increasing LIA levels beyond the current positivity threshold and its correlation to positive serotonin release assay results in cardiothoracic surgery.

METHODS

This was a multicenter, observational cohort of cardiothoracic surgery patients initiated on anticoagulation with heparin-based products. To conduct sensitivity and specificity analysis of LIA values, HIT positive was defined as a LIA value ≥1 unit/mL and HIT negative was defined as a LIA level <1 unit/mL. A receiver operating characteristic (ROC) analysis was utilized to evaluate the predictive performance of the LIA.

RESULTS

At manufactures' cutoffs of ≥1.0 unit/mL, LIA sensitivity and specificity was 93.8% and 22%, respectively, yielding a false positive rate of 78%. At a higher cutoff of 4.5 units/mL, LIA sensitivity and specificity was 75% and 71%, respectively, yielding a false positive rate of 29% and an area under the ROC curve of 0.75 (P = .01; 95% confidence interval: 0.621-0.889). Bivalirudin was initiated in 84.6% of false positive LIA results.

CONCLUSION

This study suggests that the diagnostic accuracy of the LIA can be optimized by increasing the LIA positivity threshold. Proposing a higher LIA cutoff, may mitigate unwarranted anticoagulation and bleeding outcomes.

Study on the Mechanism of False Low Measurement of IgG-Binding (Affinity) IgM Type M Protein by Turbidimetric Immunoassay

BACKGROUND

The purpose of this study was to investigate the immunological and physical characteristics of IgM-λ type M-protein from patients who were measured low in the turbidimetric immunoassay (TIA) IgM assay without error codes for high concentration to determine the cause of the false low levels and to clarify the mechanism of their occurrence.

METHODS

Materials were IgM patient samples and 8 serum samples from other IgM M-protein patients as controls. Patient samples were assayed by the TIA method, in which five manufacturers and six models (two reagent manufacturers) share the principle, and the BN ProSpec method (nephelometric method), which has a different principle. Dilution linearity tests, IgG addition experiments, isoelectric point electrophoresis, and hydrophobic chromatography were performed on patients and subjects. In addition, the binding capacity of γ-globulin by BIACORE was also examined.

RESULTS

The reaction curve of the patient IgM curved downward when the concentration of IgM exceeded 20 g/L, and no error code was obtained. In the measurement by the TIA method of five manufacturers and six models, patient IgM was measured at a false low level with no error code obtained in undiluted dilution by any of the instruments and reagents, but could be measured without any problem by the nephelometric method. In addition, in the patient IgG addition experiment, only patient IgM showed a false low level under high IgG concentration. Furthermore, the binding capacity of patient IgM to γ-globulin (IgG) by BIACORE was significantly higher than that of the control IgM-type M protein.

CONCLUSIONS

Patient IgM has an affinity (binding capacity) for IgG and forms an IgM-IgG complex under conditions of high IgG concentration. It was speculated that this complex inhibited the reaction with the anti-IgM antibody and the absorbance of the second reaction did not increase, suggesting a false low.

Ultrasensitive Detection of C-Reactive Protein by a Novel Nanoplasmonic Immunoturbidimetry Assay

Nanotechnology has attracted much attention, and may become the key to a whole new world in the fields of food, agriculture, building materials, machinery, medicine, and electrical engineering, because of its unique physical and chemical properties, including high surface area and outstanding electrical and optical properties. The bottom-up approach in nanofabrication involves the growth of particles, and we were inspired to propose a novel nanoplasmonic method to detect the formation of nanoparticles in real time. This innovative idea may contribute to the promotion of nanotechnology development. An increase in nanometer particle size leads to optical extinction or density (OD)-value changes in our nanosensor chip at a specific wavelength measured in a generic microplate reader. Moreover, in applying this method, an ultrasensitive nanoplasmonic immunoturbidimetry assay (NanoPITA) was carried out for the high-throughput quantification of hypersensitive C-reactive protein (CRP), a well-known biomarker of cardiovascular, inflammatory, and tumor diseases. The one-step detection of the CRP concentration was completed in 10 min with high fidelity, using the endpoint analysis method. The new NanoPITA method not only produced a linear range from 1 ng/mL to 500 ng/mL CRP with the detection limit reduced to 0.54 ng/mL, which was an improvement of over 1000 times, with respect to regular immunoturbidity measurement, but was also effective in blood detection. This attractive method, combined with surface plasmon resonance and immunoturbidimetry, may become a new technology platform in the application of biological detection.

Evaluation of D-dimer levels measured by different analytical methods in COVID-19 patients

Clinicians experience some challenges due to the lack of standardization of test, although D-dimer is a prognostic marker for COVID-19. We compared the clinical and analytical performances of D-dimer results obtained from different devices, kits and methods in patients with a diagnosis of COVID-19. Thirty-nine patients with a diagnosis of COVID-19 and 24 healthy individuals were included in the study. D-dimer levels were measured with Innovance D-DIMER kit (immunoturbidimetric method) on Sysmex CS-2500 and BCS XP and VIDAS D-Dimer Exclusion II kit (enzyme-linked fluorescence method) on mini VIDAS. The studies of precision, method comparison and clinic performance were performed. The variation coefficients in all systems were within the acceptable imprecision (7.8%). Bias%(12.5%) between BCS XP and Sysmex CS-2500 was lower than the acceptable Bias%(15.5%). Bias% values (19.2% and 33.3%, respectively) between Mini VIDAS with BCS XP and Sysmex CS-2500 were higher than the acceptable Bias%. The correlation coefficients among all systems were 0.89-0.98. For 500 ng/ml FEU, there was almost perfect agreement between BCS XP and Sysmex CS-2500, a moderate agreement between Mini VIDAS and BCS XP and Sysmex CS-2500. The cut-off values for distinguishing between individuals with and withoutCOVID-19 were Mini VIDAS, Sysmex CS-2500 and BCS XP 529, 380 and 390 ng/ml FEU, respectively. The immunoturbidimetric method can be used as an alternative to the enzyme-linked fluorescent method because of satisfactory agreement at the different thresholds proposed for venous thromboembolism. However, it is recommended to follow up COVID-19 with the D-dimer results obtained by the same assay system.

Reference Intervals of Apolipoprotein E in Healthy Chinese Han Adults

BACKGROUND

Reference intervals (RIs) of Apo E levels are an important parameter for the clinical evaluation of patient health, and the RIs of serum Apo E could be variable in different population. We plan to establish RIs of apolipoprotein E (Apo E) according to the CLSI EP28-A3 guideline in healthy Chinese Han adults.

METHODS

Serum Apo E values of 1,206 healthy adults (from 19 to 87 years old) were measured by immunoturbidimetry. The relationship between Apo E and age was analyzed by using Spearman's correlation. The differences between the gender and age groups were compared using Mann-Whitney U test/Kruskal-Wallis H test. We calculated recommended nonparametric Q2.5 and Q97.5 percentile intervals and the 90% confidence intervals (CI) of lower and upper limits to define the age- and gender- related RIs.

RESULTS

The level of Apo E was higher in females than males. Apo E was significantly associated with aging in adult females (r = 0.108, p < 0.05), but not in males (p = 0.518). The RIs of Apo E for females were 0.0268 - 0.0619, 0.0247 - 0.0603, and 0.0269 - 0.0658 g/L for 18 - 29, 30 - 59, and ≥ 60 years old, respectively, that for males was 0.0242 - 0.0579 g/L.

CONCLUSIONS

Our results established the age- and gender-specific RIs of serum Apo E in healthy Chinese Han adults in our laboratory.

The association of high D-dimer level with high risk of ischemic stroke in nonvalvular atrial fibrillation patients: A retrospective study

This study aimed to explore the relationship of D-dimer level with the risk stratification of ischemic stroke, and determine whether high D-dimer levels could be used as a risk factor of ischemic stroke in patients with nonvalvular atrial fibrillation (NVAF).This single-center, retrospective study recruited NVAF patients who did not undergo anticoagulant therapy. These patients were divided into 2 groups: ischemic stroke group and no-stroke group. The medical records of each patient were reviewed, demographic and clinical analyses were performed, and the laboratory results were summarized.A total of 323 eligible in-patients with NVAF, who did not receive anticoagulant therapy, were recruited (206 male and 117 female patients, median age was 75.18 ± 10.46 years old). Among these patients, 78 patients suffered from acute ischemic stroke. D-dimer level increased with age, and was positively correlated with the risk stratification of stroke, CHADS2 score (rs = 0.441, P < .001), and CHA2DS2-VASC score (rs = 0.412, P < .001), even after adjustment for age and gender (rs = 0.422, P < .001). The difference in baseline D-dimer level between these 2 groups was not statistically significant (0.70 vs 0.66 mg/L, P = .330), but this significantly increased when patients suffered from stroke (1.34 vs 0.70 mg/L, P < .001). The D-dimer level after stroke (≥6 months) was also higher than the baseline (1.16 vs 0.68 mg/L, P = .514) in 6 months, and this level nearly returned to baseline level after one year (0.69 vs 0.68 mg/L, P = .158). However, logistic regression revealed that only the D-dimer level at stroke onset and OMI were independent risk factors for ischemic stroke (P < .001), while the increase from baseline D-dimer levels was not an independent risk factor (P = .125).D-dimer level is positively correlated with the risk stratification of ischemic stroke, but has no predictive value on the occurrence of ischemic stroke in patients with NVAF.

Association between epicardial adipose tissue, high-sensitivity C-reactive protein and myocardial dysfunction in middle-aged men with suspected metabolic syndrome

BACKGROUND

As body fat composition and metabolism differ between men and women, we evaluated sex-related differences in the association among epicardial adipose tissue (EAT), secretome profile, and myocardial function of subjects with suspected metabolic syndrome.

METHODS

We evaluated 277 participants (men, n = 140; 56.1 ± 4.7 years) who underwent conventional echocardiography and two-dimensional speckle tracking from the Seoul Metabolic Syndrome cohort. EAT was measured from the right ventricular free wall perpendicular to the aortic annulus at end systole. Global longitudinal strain (GLS) was obtained from 18 apical segments. Apolipoprotein A1, apolipoprotein B, adiponectin, and high-sensitivity C-reactive protein (hs-CRP) levels were measured using immunoturbidimetry assay.

RESULTS

Mean age, body mass index, and hs-CRP level did not differ by sex. Waist circumference, fasting blood glucose level, and triglyceride/high-density lipoprotein cholesterol ratio were higher, and apolipoprotein AI and adiponectin levels were lower in men. No significant difference in mean EAT thickness was found (7.02 ± 1.81 vs. 7.13 ± 1.70 mm, p = 0.613). Men had a higher left ventricular (LV) mass index and lower GLS. EAT thickness was associated with hs-CRP level in men alone (ß = 0.206, p = 0.015). LV mass index (ß = 2.311, p = 0.037) and function represented by e' (ß = - 0.279, p = 0.001) and GLS (ß = - 0.332, p < 0.001) were independently associated with EAT thickness in men alone.

CONCLUSIONS

In middle-aged subjects with suspected metabolic syndrome, EAT was associated with inflammation represented by hs-CRP level, LV mass, and subclinical myocardial dysfunction only in men, suggesting that the inflammatory activity of EAT induced myocardial remodeling and dysfunction in middle-aged subjects but was attenuated in women. Trial registration NCT02077530 (date of registration: November 1, 2013).

Circulating Fetuin-A and Risk of Type 2 Diabetes: A Mendelian Randomization Analysis

Fetuin-A, a hepatic-origin protein, is strongly positively associated with risk of type 2 diabetes in human observational studies, but it is unknown whether this association is causal. We aimed to study the potential causal relation of circulating fetuin-A to risk of type 2 diabetes in a Mendelian randomization study with single nucleotide polymorphisms located in the fetuin-A-encoding AHSG gene. We used data from eight European countries of the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study including 10,020 incident cases. Plasma fetuin-A concentration was measured in a subset of 965 subcohort participants and 654 case subjects. A genetic score of the AHSG single nucleotide polymorphisms was strongly associated with fetuin-A (28% explained variation). Using the genetic score as instrumental variable of fetuin-A, we observed no significant association of a 50 µg/mL higher fetuin-A concentration with diabetes risk (hazard ratio 1.02 [95% CI 0.97, 1.07]). Combining our results with those from the DIAbetes Genetics Replication And Meta-analysis (DIAGRAM) consortium (12,171 case subjects) also did not suggest a clear significant relation of fetuin-A with diabetes risk. In conclusion, although there is mechanistic evidence for an effect of fetuin-A on insulin sensitivity and secretion, this study does not support a strong, relevant relationship between circulating fetuin-A and diabetes risk in the general population.

Validation of an Automated Immunoturbidimetric Assay for Fibrinogen/Fibrin Degradation Products Measurement and its Correlation to a Semi-Quantitative Latex Agglutination Test

BACKGROUND

Laboratory determination of fibrinogen/fibrin degradation product (FDP) levels is important as a hyperfibrinolytic state marker. The aim of the study was to verify the analytical performance of an automated immunoturbidimetric assay (AIMT) for FDP and its comparison to a latex agglutination semiquantitative (SLAT) test.

METHODS

Total precision and accuracy was calculated following the EP 15-A2 protocol at two levels of controls. The protocol EP6 was performed for linearity. For semi-quantitative methods comparison, 71 consecutive samples were used. Concordance between methods results in term of positive and negative, and in categories, from <10 to > 160 µg/mL, was calculated through Cohen kappa coefficient ().

RESULTS

Total CV%: low control (10.8 µg/mL) 8.0 and 3.7 vs. 4.8 and high control (31.3 µg/mL) 2.7 and 3.8 vs. 3.6, for coagulometer ACL TOP 500 and 300 vs. manufacturer claimed, respectively. Linearity between 0 and 125 µg/mL showed polynomial fit analysis applicable. When correlating AIMT to SLAT, a good concordance was observed:  of results expressed as positive-negative = 79.5% with 90.1% of agreement (p < 0.001), of results expressed as categories = 72.2% (p < 0.001) with 80.3% concordance.

CONCLUSIONS

AIMT presented good analytical performance, and the concordance with SLAT by comparison of patients' samples results was also good. The implementation of IMMT in the clinical laboratory is suitable and reliable.

Can the Thiol/Disulfide Imbalance Be a Predictor of Colchicine Resistance in Familial Mediterranean Fever?

Familial Mediterranean fever (FMF) is a chronic autoinflammatory condition characterized by fever attacks and recurrent polyserositis. Subclinical inflammation that persists during attack-free periods can result in oxidative stress (OS) damage. Thiol groups bind to reactive oxygen radicals and protect cells and tissues from OS damage. The aim of this study was to investigate the relationship between thiol-disulfide balance and colchicine resistance in FMF patients during an attack or attack-free period. A newly developed spectrophotometric method was used to measure native thiol (NT) and disulfide (DS) levels in FMF patients and an age-sex matched group of healthy controls. NT and DS levels were compared in FMF patients 1) with vs. without colchicine resistance; and 2) during an attack (FMF-AP) vs. attack-free period (FMF-AFP). A total of 118 FMF patients and 60 healthy controls were studied. NT (P < 0.001) and total thiol (TT) (P < 0.001) levels in FMF patients were significantly lower compared to healthy controls. NT (P = 0.030) and TT (P = 0.010) levels of FMF-AP patients were significantly lower than that of FMF-AFP patients. FMF-AP patients had significantly higher DS levels than FMF-AFP patients (P = 0.039). Compared to FMF patients without colchicine resistance, elevated levels of DS (P = 0.019) but not NT (P = 0.620) and TT (P = 0.718) were found in those with colchicine resistance. Thiol-disulfide homeostasis is altered in FMF patients during an attack period and this imbalance may be associated with colchicine resistance.

National continuous surveys on internal quality control for HbA1c in 306 clinical laboratories of China from 2012 to 2016: Continual improvement

BACKGROUND

This study aimed to evaluate whether the quality performance of clinical laboratories in China has been greatly improved and whether Internal Quality Control (IQC) practice of HbA1c has also been changed since National Center for Clinical Laboratories (NCCL) of China organized laboratories to report IQC data for HbA1c in 2012.

METHODS

Internal Quality Control information of 306 External Quality Assessment (EQA) participant laboratories which kept reporting IQC data in February from 2012 to 2016 were collected by Web-based EQA system. Then percentages of laboratories meeting four different imprecision specifications for current coefficient of variations (CVs) of HbA1c measurements were calculated. Finally, we comprehensively analyzed analytical systems and IQC practice of HbA1c measurements.

RESULTS

The current CVs of HbA1c tests have decreased significantly from 2012 to 2016. And percentages of laboratories meeting four imprecision specifications for CVs all showed the increasing tendency year by year. As for analytical system, 52.1% (159/306) laboratories changed their systems with the change in principle of assay. And many laboratories began to use cation exchange high-performance liquid chromatography (CE-HPLC) instead of Immunoturbidimetry, because CE-HPLC owed a lower intra-laboratory CVs. The data of IQC practice, such as IQC rules and frequency, also showed significant variability among years with overall tendency of meeting requirements.

CONCLUSION

The imprecision performance of HbA1c tests has been improved in these 5 years with the change in IQC practice, but it is still disappointing in China. Therefore, laboratories should actively find existing problems and take action to promote performance of HbA1c measurements.

Creatinine-Based and Cystatin C-Based GFR Estimating Equations and Their Non-GFR Determinants in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

eGFR equations have been evaluated in kidney transplant recipients with variable performance. We assessed the performance of the Modification of Diet in Renal Disease equation and the Chronic Kidney Disease Epidemiology Collaboration equations on the basis of creatinine, cystatin C, and both (eGFR creatinine-cystatin C) compared with measured GFR by iothalamate clearance and evaluated their non-GFR determinants and associations across 15 cardiovascular risk factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional cohort of 1139 kidney transplant recipients >1 year after transplant was analyzed. eGFR bias, precision, and accuracy (percentage of estimates within 30% of measured GFR) were assessed. Interaction of each cardiovascular risk factor with eGFR relative to measured GFR was determined.

RESULTS

Median measured GFR was 55.0 ml/min per 1.73 m(2). eGFR creatinine overestimated measured GFR by 3.1% (percentage of estimates within 30% of measured GFR of 80.4%), and eGFR Modification of Diet in Renal Disease underestimated measured GFR by 2.2% (percentage of estimates within 30% of measured GFR of 80.4%). eGFR cystatin C underestimated measured GFR by -13.7% (percentage of estimates within 30% of measured GFR of 77.1%), and eGFR creatinine-cystatin C underestimated measured GFR by -8.1% (percentage of estimates within 30% of measured GFR of 86.5%). Lower measured GFR associated with older age, women, obesity, longer time after transplant, lower HDL, lower hemoglobin, lower albumin, higher triglycerides, higher proteinuria, and an elevated cardiac troponin T level but did not associate with diabetes, smoking, cardiovascular events, pretransplant dialysis, or hemoglobin A1c. These risk factor associations differed for five risk factors with eGFR creatinine, six risk factors for eGFR Modification of Diet in Renal Disease, ten risk factors for eGFR cystatin C, and four risk factors for eGFR creatinine-cystatin C.

CONCLUSIONS

Thus, eGFR creatinine and eGFR creatinine-cystatin C are preferred over eGFR cystatin C in kidney transplant recipients because they are less biased, more accurate, and more consistently reflect the same risk factor associations seen with measured GFR.