Latex Assay Research Articles

Soluble p-selectin, D-dimer, and high-sensitivity C-reactive protein after acute deep vein thrombosis of the lower limb

Soluble p-selectin (sP-selectin), D-dimer, and C-reactive protein (CRP) are elevated in deep vein thrombosis (DVT), and may play a role as risk predictors of recurrent venous thromboembolism. However, these parameters have only been assessed at manifestation or at single time points after DVT so far. We therefore investigated the course of sP-selectin, D-dimer, and high-sensitivity (hs)-CRP after acute unprovoked DVT of the lower limb. In this prospective, longitudinal study, sP-selectin, D-dimer, and hs-CRP were determined by enzyme-linked immunosorbent assay, quantitative latex assay, and particle enhanced immunonephelometry, respectively, in 44 patients with sonographically confirmed acute DVT at the time of diagnosis, and 1, 3, 6, and 12 months later. sP-selectin and hs-CRP were also measured in 88 age- and gender-matched healthy controls. Further, color duplex sonography was performed in all patients at each time point. At DVT diagnosis, sP-selectin and hs-CRP were significantly higher in patients compared with healthy controls. From baseline to 1 month, both parameters decreased significantly. In patients with oral anticoagulation (OAC) for 6 months (n = 35), levels of sP-selectin increased significantly after cessation of anticoagulant therapy (P = .002), while sP-selectin was similar to healthy controls in patients with ongoing OAC (n = 9) at 12 months (P = .49). In contrast, hs-CRP in both subgroups remained constantly low at levels seen in healthy controls. The course of D-dimer was similar to sP-selectin. Color duplex sonography showed no ongoing thrombus formation in any patient. Thirty-four (77.3%), 29 (65.9%), 26 (59.1%), and 25 (56.8%) patients had residual thrombosis 1, 3, 6, and 12 months after the acute event, respectively. D-dimer was significantly higher in patients with residual thrombosis compared with patients without residual thrombosis 1 month after DVT (0.58 μg/mL [range, 0.2-9.67 μg/mL] vs 0.25 μg/mL [range, 0.2-0.62 μg/mL]; P = .02). At all other time points, the levels of D-dimer and sP-selectin did not differ significantly between patients without and with residual thrombosis (all P > .05). Concentrations of sP-selectin and D-dimer after acute DVT seem to be strongly influenced by treatment with vitamin K antagonists. After withdrawal of oral anticoagulation, they rise again and could therefore reflect a prothrombotic state, which is susceptible to pharmacologic therapy.

Performance evaluation of a turbidimetric cystatin C assay on different high-throughput platforms

Objective. The goal with this study was to evaluate the analytical performance of a new cystatin C immunoassay (Tina-quant® a Cystatin C, Roche Diagnostics GmbH). The evaluation was carried out at four centers according to a standardized protocol. Material and methods. The Tina-quant® a Cystatin C is a latex particle-enhanced immunoturbidimetric assay. Roche cobas® 6000, MODULAR ANALYTICS SWA and COBAS INTEGRA® instruments were included in the study. Method comparison studies were carried out against two turbidimetric methods (Dako Cystatin C, Gentian Cystatin C), and one nephelometric method (Siemens N-Latex Cystatin C). Results. Linearity was proven throughout the measuring range from 0.4 to 8 mg/L. Within-run CVs ranged from 0.7–2.8%, and total CVs from 1.4–4.7 % (concentration range 0.6–3.9 mg/L). Comparable results were obtained with paired serum and Li-heparinate plasma samples. Good agreement was achieved in the comparisons between the Tina-quant® a Cystatin C assay and the other commercially available cystatin C assays, two different turbidimetric methods (slope range 0.88–1.04, intercept < 0.17 mg/L, r ≥ 0.993) and one nephelometric assay (slope range 0.90–1.05, intercept < 0.21 mg/L, r ≥ 0.986). Conclusions. The Tina-quant® a Cystatin C assay was shown to be precise and accurate with proven linearity over the measuring range. Good comparability was obtained with other commercially available assays for the determination of cystatin C. The Tina-quant® a Cystatin C assay is very well suited for clinical use on routine clinical chemistry analysers to detect renal dysfunction with a 24 h availability.

Serological and parasitological survey of dourine in the Arsi–Bale highlands of Ethiopia

This study was conducted from August 2005 to January 2007 to determine prevalence and distribution of dourine in horses and to investigate the occurrence of clinical and carrier cases in donkeys and mules in the Arsi-Bale highlands. Study methodology was based on questionnaire, serological, clinical and parasitological survey. The questionnaire indicated that dourine is a major health problem of equines in the Arsi-Bale highlands. Though dourine is commonly observed throughout the year, it has a seasonal character and occurs mostly during the breeding season from June to late September. Serological screening of 646 horses showed a seroprevalence of 184 (28%), 161 (25%) and 125 (19%) for card agglutination test for trypanosomosis, LATEX and enzyme-linked immunosorbent assay, respectively. Risk factors were parity number, previous history of abortion and body condition score. No trypanosomes could be detected by Giemsa staining or by haematocrit centrifugation technique. Ten puppies inoculated with blood samples, genital washes and oedematous fluids remained parasitologically negative. Different characteristic signs of dourine were observed. During the genital stage, mares showed vaginal oedema, discharge and presence of depigmented scars over the external genitalia. In stallions, oedema of the scrotum and prepuce, prepucial and urethral discharge, and ulceration of the genital mucosae mainly of the penile were observed. In both sexes, lameness in one or both legs, partial dragging and stiffness of the hind legs and incoordination were the dominant signs observed as nervous form of the disease.

Nosocomial Gastroenteritis in Children With and Without Rotavirus Infection

To the Editors: Rotavirus (RV) is the most common cause of severe gastroenteritis in children and the proportion of childhood gastroenteritis hospitalizations attributed to RV has recently increased from 22% to 39%.1 RV gastroenteritis is also one of the leading nosocomial infections in the pediatric age group.2 Although the typical symptoms in nosocomial RV gastroenteritis are well recognized,2 information regarding the differences of clinical presentation and evolution of nosocomial gastroenteritis with and without RV infection is scarce. We performed a retrospective cohort study on nosocomial infection in a pediatric university hospital in Salvador, Brazil, between October 2002 and September 2005. Nosocomial gastroenteritis was defined as >3 watery or looser-than-normal stools and/or a single episode of forceful vomiting within a 24-hour period after the first 72 hours of hospitalization. RV antigen was searched for in stool specimens by a rapid latex assay (ROTA Rich, Richmond Diagnostics, Spain). Data were collected from an epidemiologic surveillance form of the Nosocomial Infection Control Service and laboratory database; details regarding the child's illness were collected from the patient charts. All hospitalized patients were actively surveyed to detect occurrence of nosocomial infection. Fever was defined as axillary temperature >37.5°C. The study was approved by the Ethics Committee of the Federal University of Bahia. Overall, 125 cases of nosocomial gastroenteritis were identified, of which 66 had the rotavirus assay performed and the patient chart accessible for review. Therefore, the study group comprised 66 cases, of which 49 (74%) were RV positive. None of the patients had chronic gastrointestinal tract disease, immunodeficiency, or bacterial intestinal infection. The median age was 7 (mean, 11 ± 13; range, 0.3–105) months and there were 39 (59%) males. There was no difference in age (month) (10 ± 8 vs. 16 ± 27) or male gender (57% vs. 65%) distribution when patients with and without RV infection were compared, as well as in the length of signs and symptoms or duration of hospitalization (data not shown). Vomiting (69% vs. 41%, P = 0.04, OR 3.2, 95% CI 1.04–10.1), dehydration (37% vs. 6%, P = 0.02, OR 9.3, 95% CI 1.1–76), the combination of symptoms fever, vomiting, and diarrhea (49% vs. 18%, P = 0.02, OR 4.5, 95% CI 1.1–18) and fever, diarrhea, and dehydration (29% vs. 0%, P = 0.01, OR 1.5, 95% CI 1.2–1.8) were associated with RV infection. All patients were discharged from hospital after improvement. Vomiting and fever have been recognized as prominent symptoms in RV-associated hospitalized cases.3 Among community-acquired RV infected hospitalized children, the combination of fever, vomiting, and diarrhea was the most frequent clinical presentation (63%).4 We found similar features among our patients with nosocomial RV gastroenteritis. This finding may be explained by the nosocomial RV acquisition because of circulation of community-acquired RV in the hospital.3 Despite the association with dehydration, the length of hospitalization was not different between patients with and without RV because of early diagnosis and rapid rehydration. Licia L. Moreira, RN Infection Control Service of the Professor Hosannah de Oliveira Pediatric Center Federal University of Bahia Salvador, Brazil Eduardo M. Netto, MD, PhD Infectious Diseases Unit University Hospital Federal University of Bahia Salvador, Brazil Cristiana M. Nascimento-Carvalho, MD, PhD Department of Pediatrics School of Medicine Federal University of Bahia Salvador, Brazil

Laboratory evaluation of a simple and rapid latex agglutination assay for the serodiagnosis of typhoid fever

A latex agglutination assay for the serodiagnosis of typhoid fever was evaluated on samples collected from patients with clinical suspicion of typhoid fever in South Sulawesi, Indonesia, where the disease is endemic. The latex assay is very easy to use, gives a rapid result and may be used as a point-of-care diagnostic test. For acute phase samples collected on average 6 days after the onset of illness, the sensitivity is 42.5% for culture-confirmed patients with typhoid fever and the specificity is 96.9%. The sensitivity improved with the duration of illness from 30.8% for samples collected during the first 4-5 days of illness to 45.5% for samples collected between days 7 and 9, and to 84.6% for the samples collected more than 9 days after the onset of illness. Testing of follow-up samples may further improve sensitivity by demonstrating seroconversion.

Systematic Survey of Nonspecific Agglutination by Candida spp. in Latex Assays

In order to demonstrate that cells of Candida spp. may show considerable nonspecific agglutination in latex agglutination tests, 150 clinical and reference isolates of 12 yeast species were systematically studied by applying various test parameters. In fact, 40 (26.7%) of these isolates revealed nonspecific results, significantly associated with the time allowed for agglutination.

Determination of bovine lactoferrin in lactoferrin-supplemented dairy products and raw milk by an automated latex assay

Latex immune agglutination method with a multipurpose auto-analyser (the automated latex assay) was validated for determination of bovine lactoferrin (BLF) in various dairy products. Reproducibility-within-laboratory (intermediate precision) due to day for infant formula, UHT milk and yogurt supplemented with BLF at 50 mg/100 g for infant formula and UHT milk, and at 100 mg/100 g for yogurt were 1.62 to 3.10 mg/100 g. Reproducibility-within-laboratory due to analysis (morning, noon, and evening) for raw milk was 1.59 mg/100 g. Trueness, accuracy in determining known amounts added for BLF-supplemented dairy products was -4.7 to -2.0 mg/100 g. BLF concentration in raw milks was 20.3 to 21.8 mg/100 g. Although interference by the matrixes took place in infant formula and raw milk, BLF assays were accurately carried out by 2000-fold dilution or standard-addition method. Automated latex assay for BLF is simple, rapid, precise and accurate enough for a routine method in various dairy products containing BLF.

Charge Selective Function in Childhood Glomerular Diseases

The charge selectivity (CS) function in human renal disease has not been unequivocally demonstrated to date. However, the clearance ratio of IgA to IgG may be theoretically useful in estimating CS in humans, since IgA and IgG have similar sizes and tertiary structures, but distinct isoelectric points (3.5-5.5 [IgA] and 4.5-9.0 [IgG]), and Stokes-Einstein radius: 61 A (IgA) and 49-60 A (IgG). Two-dimensional electrophoresis with the following immunoblotting revealed that the considerably anionic portion (isoelectric points [pI] <4.0) of IgA, visible in serum, was absent in the urine in steroid-sensitive nephrotic syndrome (SSNS) but present in the same during IgA nephropathy (IgAN) and membranoproliferative glomerulonephritis (MPGN). A latex assay revealed the CS index (CSI) was significantly low in patients with podocyte disease (group A), including SSNS, focal and segmental glomerulosclerosis (FSGS) and Finnish-type congenital nephrotic syndrome (FCNS), but high in those with Alport syndrome (AS), IgAN, Henoch-Schönlein purpura nephritis (HSPN), and MPGN (group B). The linear regression analysis of the IgA size selectivity index (IgA SSI; clearance ratio of IgA to transferrin) and SSI (clearance ratio of IgG to transferrin), which represents the clearance ratio of IgA to IgG referring to the transferrin clearance, revealed the influence of the charge more accurately. Indeed, the slope of the regression lines of IgA SSI (y) to SSI (x) were concluded to be y = 0.39x (group A) and y = 1.05x (group B), respectively. These results suggested that the charge selective barrier among podocyte diseases (group A) is preserved to some degree, but lost in cases of nephritis and AS (group B).

Latex Immunoagglutination Assays*

Latex immunoagglutination assays continue to be widely used in biology and medicine for the detection of small quantities of an antibody or antigen of interest in fluid test samples. Main characteristics of preparation and use of these assays are examined here. Physical adsorption of proteins onto latex particles surface, with special relevance to immunoglobulins, is analyzed with major attention to those factors that influence adsorption: medium conditions such as pH and ionic strength, surface characteristics as type and amount of charge, or hydrophobicity. Different functionalized latexes for covalent linking are also presented, as well as the corresponding chemical reactions. Techniques for the detection and quantification of the immunoreaction are briefly summarized, including visual observation, light scattering, turbidimetry, nephelometry, and angular anisotropy. Finally, some problems of colloidal stability of these latex assays are analyzed, as well as the different solutions applied by scientists to solve them. *Reprinted with permission from Colloidal Biomolecules, Biomaterials, and Biomedical Applications, A. Elaissari, Ed., Marcel Dekker, Inc, New York, 2004, pp. 53–101

A rapid agglutination assay to detect anti-streptokinase antibodies

Streptokinase resistance may cause suboptimal thrombolytic therapy. To develop a rapid latex-bead assay to detect streptokinase antibodies. Sera were obtained from 16 patients presenting with acute myocardial infarction (MI) before treatment with streptokinase and 1 and 6 months post treatment, and from 100 controls. Sera were assayed for anti-streptokinase antibodies using a functional streptokinase-neutralising assay. Streptokinase-neutralising activity was low in controls (54 +/- 5U/ml) and patients prior to treatment (101 +/- 18), increasing to 2,110 +/- 823 and 1,017 +/- 169 at 1 and 6 months (mean +/- SEM). The latex assay had a sensitivity of 94% and a specificity of 93% for detecting individuals with > 350U/ml of streptokinase resistance, which is sufficient to neutralise the drug clinically. Estimation of streptokinase resistance using an enzyme immunoassay and a latex bead assay correlated well with serum neutralising activity. This assay can rapidly identify patients who have a high level of streptokinase-neutralising activity.

Plasma d-Dimer Levels Correlate With Outcomes in Patients With Community-Acquired Pneumonia

The aim of this study was to investigate the prognostic value of plasma d-dimer levels in patients with community-acquired pneumonia (CAP). Prospective observational study. Hospital Lluis Alcanyis of Xativa, Spain. Consecutive adult patients admitted to the hospital with CAP from January 2000 to October 2002. A total of 302 patients were included. Plasma d-dimer was measured using an automated latex assay. The relationships between plasma d-dimer and prognostic variables included in the pneumonia severity index (PSI) were examined using univariate and multivariate linear and logistic regression analyses. d-Dimer levels were negative (ie, < 500 ng/mL) in 16.9% of the patients. In nonsurvivors, the d-dimer plasma level mean value was 3,786 ng/mL, while in survivors it was 1,609 ng/mL (p < 0.0001). A significant relationship was found between the presence of elevated d-dimer levels and the PSI and APACHE (acute physiology and chronic health evaluation) II score. Elevated d-dimer levels were associated with radiologic pneumonia extension. The d-dimer predictive value for mechanical ventilation therapy showed an area under the curve of 0.78 (95% confidence interval, 0.71 to 0.81). d-Dimer plasma levels could be useful for predicting clinical outcome in patients with CAP.

Rapid determination of bovine lactoferrin in dairy products by an automated quantitative agglutination assay based on latex beads coated with F(ab')2 fragments.

This study evaluated an automated immunoassay for bovine lactoferrin (LF) in dairy products based on latex beads coated with F(ab')2 fragments. F(ab')2 fragments were obtained by pepsin digestion of rabbit anti-bovine LF (IgG fraction) and polystyrene latex beads were coated with the F(ab')2 fragments. We used the beads to develop a rapid and homogeneous light scatter immunoassay employing an autoanalyzer (the Automated Latex assay). The Automated Latex assay was easy to perform and could rapidly determine bovine lactoferrin in lactoferrin-supplemented products. It was sensitive enough for testing products and showed good precision.

Quantitative Latex d-dimer Test Can Rule Out DVT

d-dimer testing has not yet reached its full diagnostic potential in clinical practice because the most reliable versions are time-consuming. In this prospective cohort study, researchers assessed whether a 30-minute, quantitative, latex microparticle d-dimer assay could rule out deep-vein thrombosis (DVT). Of 943 adult outpatients with first suspected episodes of DVT, the researchers included 558 (59%) who were not pregnant, who were not …

How to detect current toxoplasma infection

This study seeks to identify the best way to detect current toxoplasma infection for district general hospital laboratories. One hundred ‘ordinary’ and 174 ‘difficult’ sera are categorised into either an ‘evidence’ or ‘no evidence’ group for current toxoplasma infection. Twelve test protocols are investigated using different combinations of one whole antibody latex test (Eiken Toxoreagent), one in-house specific IgG enzyme-linked immunosorbent assay (ELISA) and three specific IgM assays (Toxo-ISAGA, in-house BAM ELISA IgM and Toxonostika ELISA M). The Eiken latex and in-house IgG assays produced significantly fewer false-negative results than were obtained with the single IgM test or the IgG and IgM test protocols (P<0.05), but a greater number of false-positive results (102/274 and 115/274, respectively). Of the IgM assay test protocols, the three IgM assays in combination produced the least number of false-negative results (1/274). However, a significantly greater number of false-positive results were produced than with one or two IgM tests or an IgG and any IgM test in combination (P<0.001). We recommend testing with three IgM tests, or a whole antibody (Eiken) or IgG-specific assay, and that positive or clinically important negative samples be referred to a reference laboratory for confirmation.

The Auto•Dimer™ latex assay for the rapid determination of D-dimer on a variety of coagulation analysers

The Auto•Dimer™ latex assay for the rapid determination of D-dimer on a variety of coagulation analysers

Performances of a new, automated latex assay for the exclusion of venous thromboembolism

The performance of a new latex-enhanced turbidimetric assay, D-Dimer PLUS, has been evaluated with two analyzers performing various coagulation assays: the BCS Analyzer and the BCT Analyzer. A precision study showed total coefficients of variation ranging from 2.7 to 11.1% with the BCS Analyzer and from 2.5 to 6.6% with the BCT Analyzer. We investigated the ability of D-Dimer PLUS to exclude venous thromboembolism in 312 outpatients suspected of either pulmonary embolism or deep venous thrombosis. Three months follow-up was available for all patients. With the BCS Analyzer, we determined a cut-off value of 190 ng/ml, which gave a sensitivity of 97.9% [95% confidence interval (CI), 92.6-99.7%], a specificity of 37.9% (95% CI, 30.9-43.8%) and a negative predictive value of 97.6% (95% CI, 91.7-99.7%). With the BCT Analyzer, at a cut-off value of 130 ng/ml, sensitivity was 96.8% (95% CI, 91.0-99.3%), specificity was 45.2% (95% CI, 38.5-51.2%) and the negative predictive value was 97% (95% CI, 91.6-99.4). This new assay is fast and fully automated, and its performance is suitable to exclude venous thromboembolism. Management studies should be performed to assess its utility.

Development of an Automated Quantitative Latex Immunoassay for Cardiac Troponin I in Serum

Currently, the measurement of troponin I (TnI) can only be accomplished through the use of heterogeneous assays on closed-system automated analyzers. The development of this new and innovative latex technology will allow the measurement of TnI on a variety of turbidimetry-based open-system instruments, greatly enhancing clinical applicability of this test. Determining the presence of TnI in the serum of patients is an important aid in the diagnosis of myocardial infarction. An advantage of TnI is its improved specificity for myocardial damage compared with creatine kinase-MB (1). In addition, there is strong evidence that future utilization of TnI will be for risk stratification to assist in the decision process for therapeutic intervention with glycoprotein II/IIIa inhibitors or low-molecular weight heparin (2)(3). In fact, the GUSTO trial, which should be completed soon, included TnI as one of the cardiac markers to be considered for risk stratification. The cardiac troponin complex is part of the contractile apparatus of the thin filament in striated muscle and consists of subunits C, T, and I. Different isoforms of TnI exist in the skeletal and cardiac muscles (fast skeletal, slow skeletal, and cardiac TnI). The distinct structural heterogeneity between these isoforms allows production of specific antibodies (4), which can be utilized by the latex assay to detect serum TnI in clinical conditions that involve myocardial damage. After …

Comparison of Diagnostic Performance of Three New Fast D-Dimer Assays in the Exclusion of Deep Vein Thrombosis

D-Dimer (DD), a soluble cross-linked fibrin degradation product, has been suggested as a reliable marker to rule out deep vein thrombosis (DVT) (1)(2)(3)(4). The disease can be ruled out in approximately one-third of outpatients suspected with DVT when the plasma concentration of DD is below an appropriate cutoff value (4). Measurement of plasma DD concentrations has been performed by two major methods: ELISA, which is highly sensitive but time-consuming; and latex agglutination, which is faster but less sensitive than ELISA (2)(4). SimpliRED, a latex assay, detects DD directly in whole blood, avoiding the plasma preparation step (5). However, this assay gives only qualitative results and adds an interindividual observation bias that may partly explain the discordant sensitivity values obtained by different investigators (3)(5)(6)(7). In the present study, we investigated the clinical utility of three new fast DD assays in the diagnosis of DVT. We compared 177 consecutive outpatients (117 women and 60 men) from the Montreal cohort in a bicentric prospective study (8). The mean age was 56 years (range, 19–87 years). The inclusion criteria were that subjects be ambulatory patients with a clinical suspicion of DVT and >16 years of age. The exclusion …

Rapid fibrin D-dimer tests for deep venous thrombosis: factors affecting diagnostic utility

Measurement of fibrin D-dimer may be a useful diagnostic test to exclude a diagnosis of deep venous thrombosis (DVT) in the emergency department setting. However, the specific assay format may influence its sensitivity and ultimate clinical utility. We tested samples from 200 patients under evaluation for DVT using three fibrin D-dimer assays: the SimpliRED TM whole blood agglutination assay, a latex agglutination assay, and the Dimertest EIA TM. Latex agglutination assays were performed in both a specialized laboratory and a routine laboratory. The negative predictive value for all tests was > 90%. The sensitivity of the SimpliRED TM assay was similar to that of the latex assay. The sensitivity of the latex assay was significantly lower when performed by generalist laboratory technologists. Thus, while D-dimer may be a useful test for the exclusion of DVT, subjective endpoint latex agglutination assays should be performed only by appropriately trained personnel.

Incidence and possible reasons for discordant results between positive FDP and negative D-dimer latex assays in clinical specimens.

In general, FDP and D-dimer values have a correlation in clinical conditions associated with disseminated intravascular coagulation(DIC) or coagulation activation. However, there are some patients with discordant results who demonstrate elevated FDP and negative D-dimer results by latex agglutination assays. The incidence and possible reasons for the discordance between FDP and D-dimer results were investigated through simultaneous measurements (n = 763) from clinical patients with suspected DIC or coagulation activation. 24.8% (189/763) of samples with elevated FDP were negative for D-dimer assays by the latex agglutination method. Further detailed analysis on randomly-selected discordant samples (n = 41) revealed that the most common reason for the discordance was the lower sensitivity of the semiquantitative latex agglutination method for D-dimer, compared with quantitative enzyme or other latex immunoassay. The other contributing factors to the discordance were accelerated fibrinogenolysis without secondary fibrinolysis, elevated soluble fibrin monomer and rheumatoid factor.