Comparison between radiometry and spectrophotometry for the determination of angiotensin-converting enzyme activity in cerebrospinal fluid.

Determination of angiotensin-converting enzyme (ACE) activity in cerebrospinal fluid (CSF) can help for establishing the diagnosis of neurosarcoidosis. We investigated the performance characteristics of two assays for ACE determination in 57 CSF, radiometry with [glycine-1-14C] benzoyl-L-histidyl-L-leucine and spectrophotometry with furylacryloyl-phenylalanyl-L-glycyl-L-glycine (FAPGG) as substrates. We compared both kinetic assays to an ELISA specific for human ACE. Within run and between run imprecisions were 14-17% for radiometry, 6-19% for spectrophotometry and 5-8% for ELISA. The limit of detection was 0.04 U/L for radiometry, 1.0 U/L for spectrophotometry and 0.156 µg/L for ELISA. The limit of quantification was 0.06 U/L for radiometry, 1.5 U/L for spectrophotometry, but not known for ELISA. The domain for quantification was 0.06-4.0 U/L for radiometry, 1.5-24 U/L for spectrophotometry and 0.156-10 µg/L for ELISA. Deming regression and Bland-Altman plots show good correlations between the three assays, but with high slopes, because both kinetic assays use different substrates and ELISA measures ACE molecule but not activity. Radiometry was more sensitive than spectrophotometry, which has a limit of detection above most pathological levels. ELISA could be an alternative to radiometry but only after complete evaluation, determination of normal values and assessment of its clinical value. We claim for standardization of ACE determination as well as in serum as in other biological fluids, in particular CSF.

[Measurement of angiotensin-I-converting enzyme in the blood: help for method validation]. / Dosage de l'enzyme de conversion de l'angiotensine-I sanguine : aide à la validation de méthode.

Blood angiotensin-converting enzyme (ACE) assay is now realized by the determination of enzyme activity on synthetic substrate, mostly furylacryloyl-phenylalanyl-L-glycyl-L-glycine (FAPGG). The matrix can be serum or heparin-plasma, with or without a separator; the assay developed on serum or plasma is not adapted to other matrix such as cerebrospinal fluid where the ACE activity is much lower. This assay has been adapted on a number of automated biochemistry analyzers with the specifications of the supplier of reagents, sometimes with modification of volumes or times for analysis. Samples can be stored at +4̊C for at least for one week, freezing at -20̊C is possible but refreezing is not advised. The assay is linear from 10 to 200 UI/L. Fidelity is excellent after calibration of the assay. Accuracy can be calculated from IQA and EQA results, and the analytical uncertainty is between 2% and 5% in function of the serum ACE value. Usual values will be soon available from studies on age brackets and sex, because ACE activity seems to be more elevated in boys during adolescence. At signature, it is interesting to have medical information on the diagnosis of sarcoidosis or its treatment including ACE inhibitors as a proof of intake; we can give a commentary on elevation of serum ACE activity from other causes than sarcoidosis and the causes for low activities.

False elevation of blood lactate reveals ethylene glycol poisoning.

Ethylene glycol poisoning is a medical emergency. Making a definitive diagnosis is challenging because few institutions have timely access to direct measurement of ethylene glycol. After ingestion, primary metabolism of ethylene glycol takes place in the liver, leading to glycolic acid and glyoxylic acid. These compounds may cross-react with L-lactate oxidase used in blood gas analyzers lactate electrodes to induce false elevation of blood lactate. We present the case of a 47-year-old male patient initially admitted to the intensive care unit for severe lactate acidosis of unknown cause (pH 6.96, lactate, 30 mmol/L). Knowledge of potent artifactual lactate results was the key to the diagnosis of ethylene glycol poisoning, and false lactate measurements were found at the central laboratory on our 3 different blood gas analyzers.

Point-of-care testing: false elevation of cardiac troponin I assayed in the emergency department.

In October 2007, an 18-year-old woman with no cardiac history was admitted to the emergency department for a major epigastric pain. The chest pain led to assay cardiac troponin I (cTnI) with the emergency department point-of-care testing analyzer (Stratus CS), which disclosed a value of 0.70 ng/mL, discordant with the atypical clinical presentation and the noncontributive electrocardiography. The biologist contacted for biological advice controlled cTnI with an Access II, which disclosed a value less than 0.04 ng/mL. These findings were confirmed with the discordant results of a new sample assayed on both analyzers. The interference of heterophilic antibodies (HAs) was suspected because these antianimal antibodies may lead to analytical errors in sandwich immunoassays using animal sources of immunoglobulins and can cause false-positive results. In this case, the HAs bind to the capture antibody and the conjugate antibody, simulating cTnI. The diagnosis of HA involvement was confirmed using Heterophilic Blocking Tube, a device that contains a blocking reagent composed of specific binders that attach HA. After treatment in Heterophilic Blocking Tube, the cTnI concentration measured by the Stratus CS decreased from 0.62 to 0.05 ng/mL. Finally, potentially invasive test or this patient's unnecessary hospitalization in cardiology was avoided. Our experience supports that collaboration between staffs of laboratories and medical departments owning point-of-care testing analyzers is essential to avoid mistaken diagnosis linked to analytical interferences and to ensure quality of results assayed outside the laboratory.

Multi-centre evaluation of recent troponin assays for the diagnosis of NSTEMI.

OBJECTIVES: We aimed to compare the use of nine different cardiac troponin (cTn) assays (2 cTnT and 7 cTnI) for the diagnosis of NSTEMI in a single multi-centre population. DESIGN AND METHODS: One hundred and fifty-eight patients were included (mean age 60 years, SD 17 years), including 23 patients (14%) with NSTEMI. RESULTS: The analytical comparison highlighted a large heterogeneity of cTn assays, as reflected by percentages of patients with detectable cTn, correlation coefficients, Passing-Bablok comparisons and concordance coefficients. Correlations within cTnI assays were good and correlation within cTnT assays was excellent. Diagnostic performances demonstrated that each cTn assay has specific threshold values. Furthermore, some assays (HS-cTnI and T, cTnI-Pathfast and cTnI-Centaur) indicated high sensitivity and negative predictive value using the limit of detection (LoD) diagnostic strategy. For the latter assays, a significant increase in specificity was found when using the 99th percentile or the H0-H3 strategies, in comparison to the LoD strategy. When applying the European Society of Cardiology H0-H3 algorithm, comparable diagnostic performances were obtained. CONCLUSION: All 9 cTn assays indicated overall good diagnostic performances for the diagnosis of NSTEMI in emergency departments when the recommended algorithm based on the variation of cTn value between two measurements at admission and 3 h later was used.

Search for biomarkers of neurosarcoidosis by proteomic analysis of cerebrospinal fluid.

Sarcoidosis is a systemic granulomatous disease, which mostly affects lung. Central nervous system can be affected causing a neurosarcoidosis in 5 to 15% of all sarcoidosis patients. The definitive diagnosis is established on histological examination of brain granulomas. Angiotensin converting enzyme is currently the most relevant biomarker to confirm a probable diagnosis; however, it lacks sensitivity and specificity. We aim to find novel biomarkers of neurosarcoidosis in cerebrospinal fluid (CSF) by proteomic analysis, combining two-dimension electrophoresis (2-DE) and mass spectrometry. We performed CSF proteomic profile of both patients (group S) and control subjects (group H). The statistical analysis of 2-D gels highlighted 42 spots significantly different between the two groups. Twenty-five spots were subjected to tryptic digestion; the peptides were analyzed by MALDI-TOF and MALDI-TOF-TOF, giving rise to 10 identifications. Among the identified proteins, low-molecular-mass-kininogen and vitamin-D-binding-protein were increased, while transthyretin was decreased. These proteins have probably an intrathecal source and could be interesting candidates. This study led to the identification of several proteins which can be used for the diagnosis and/or monitoring of neurosarcoidosis. These putative biomarkers have to be confirmed on a larger cohort and assessed for their sensitivity and specificity.

Angiotensin-converting enzyme insertion/deletion gene polymorphism in a Tunisian healthy and acute myocardial infarction population.

INTRODUCTION: The role of the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene (ACE) on acute myocardial infarction (AMI) is controversial. OBJECTIVES: To assess the effect of the ACE I/D polymorphism on AMI compared with the healthy controls and its relationship with serum ACE activity in a Tunisian population. DESIGN AND METHODS: A total of 119 patients with AMI were compared with 238 healthy controls from the same geographical area. ACE genotyping was determined by polymerase chain reaction, and serum ACE activity was measured with N-[3-(2-furylacryloyl]-L-phenylalanyl-L-glycyl-L-glycine as substrate. RESULTS: The ACE I/D polymorphism was significantly different between patients and controls (p < 0.0001). The frequencies of the DD genotype and the D allele were statistically higher in patients with AMI as compared with the controls and were associated with increased risk of AMI (DD vs. ID and II: odds ratio = 4.27, p < 0.0001, 95% confidence interval = 2.65-6.86; D vs. I: odds ratio = 3.15, p < 0.0001, 95% confidence interval = 2.26-4.40). This association was independent of other cardiovascular risk factors but dyslipidemia (p = 0.002) that was not represented in AMI patients with II genotype and in a lower extent with hypertension (p < 0.05). Serum ACE activity was significantly higher in AMI patients with ACE DD genotype compared with the subjects with ID or II genotype (p = 0.034) and was not correlated with other cardiovascular risk factors. CONCLUSIONS: ACE DD genotype associated with higher serum ACE activity is increased in the studied population and might be clinically useful as markers to assess risk for AMI.

Evaluation of the GEM Premier 4000: a compact blood gas CO-Oximeter and electrolyte analyzer for point-of-care and laboratory testing.

BACKGROUND: GEM Premier 4000 (Instrumentation Laboratory), a new blood gas/CO-Oximeter/hematocrit/electrolyte/glucose/lactate analyzer was evaluated. The only reagents required were disposable cartridges (GEM Premier 4000 PAK comprise all components necessary for analysis, including quality controls). METHODS: The evaluation was performed in two laboratories according to the Valtec protocol guidelines. Analytical performances (imprecision at three levels, linearity, inaccuracy by method comparison using patient samples, interferences) and instrument practicability were compared with three routinely used laboratory blood gas analyzers (ABL 835 and 725, Radiometer; OMNI S, Roche Diagnostics) and the centrifuged microhematocrit method. RESULTS: Within-run and between-run imprecision yielded good coefficients of variation values for all parameters. Linearity was satisfactory and within the expected ranges provided by the manufacturer. Method comparisons demonstrated close agreement (Deming's regression correlation coefficients 0.92-1.00). No interferences of lipemia, hyperbilirubinemia and hemolysis were found on CO-Oximetry parameters. Fetal hemoglobin >35% overestimated carboxyhemoglobin measurements, but the magnitude of error was reduced with the fetal hemoglobin correction analysis mode. CONCLUSION: The GEM Premier 4000 analytical performance was validated for all parameters with the accuracy and the reliability of traditional systems. This blood gas analyzer fulfills most of the requirements for both point-of-care and laboratory use.

Evaluation of the blood gas analyzer Gem PREMIER 3000.

During the past few decades, new technologies have allowed the fabrication of miniaturized sensors and the development of analyzers well designed for point-of-care testing (POCT). They combined the ease-of-use and portability required for POC with the accuracy and the reliability of traditional systems. Instrumentation Laboratory introduced the GEM Premier 3000, a compact and portable system to rapidly analyze pH, pCO2, PO2, Ca2+, Na2+, K+, lactate, glucose and hematocrit, from 135 microl of whole blood with a simple component: a cartridge, the GEM Premier Pak. The analytical performance was compared with the Radiometer ABL 725 instrument for blood gas/ electrolytes/metabolites, and for hematocrit with the centrifuged microhematocrit method. Aqueous quality control materials (Instrumentation Laboratory) were used for precision and recovery studies. The evaluation was performed according to the Valtec protocol, designed by the French Society of Clinical Biology, for imprecision, linearity and accuracy. With-in-run and between-run imprecisions for all the parameters gave good CV values. Linearity was good and results comparison showed close agreement with correlation coefficients between 0.91 and 0.99. The analyzer is very easy to use; the simplicity and the convenience of only one consumable make the GEM Premier 3000 very suitable for a STAT laboratory or for POCT.