Antibody-mediated interferences affecting cardiac troponin assays: recommendations from the IFCC Committee on Clinical Applications of Cardiac Biomarkers.

The International Federation of Clinical Chemistry Committee on Clinical Applications of Cardiac Biomarkers (IFCC C-CB) provides educational documents to facilitate the interpretation and use of cardiac biomarkers in clinical laboratories and practice. Our aim is to improve the understanding of certain key analytical and clinical aspects of cardiac biomarkers and how these may interplay. Measurements of cardiac troponin (cTn) have a prominent place in the clinical work-up of patients with suspected acute coronary syndrome. It is therefore important that clinical laboratories know how to recognize and assess analytical issues. Two emerging analytical issues resulting in falsely high cTn concentrations, often several fold higher than the upper reference limit (URL), are antibody-mediated assay interference due to long-lived cTn-antibody complexes, called macrotroponin, and crosslinking antibodies that are frequently referred to as heterophilic antibodies. We provide an overview of antibody-mediated cTn assay interference and provide recommendations on how to confirm the interference and interpret the results.

Total bilirubin assay differences may cause inconsistent treatment decisions in neonatal hyperbilirubinaemia.

OBJECTIVES: To assess interlaboratory variability of total serum bilirubin (TSB) results in newborns. Initiated following a clinical incident in which a neonate was transferred to a tertiary hospital for treatment of severe hyperbilirubinemia but on arrival was reclassified into a lower risk category due to a 20% difference in TSB between laboratories. METHODS: Fresh residual plasma samples from hospital-born infants were pooled to obtain 11 samples across a range of total bilirubin concentrations. Aliquots were light-protected and measured on 7 commercial platforms at 4 accredited medical laboratories. Data from The Royal College of Pathologists of Australasia Quality Assurance Programs' (RCPAQAP) Neonatal Bilirubin program was analysed. RESULTS: Twenty-four to 30% difference in results for individual samples, largely due to calibration differences between assays. When interpreted according to guidelines, results from different platforms would have led to different clinical interventions in some cases. RCPAQAP results showed significant within-method bias but were not shown to be commutable with patient samples. CONCLUSIONS: There are clinically significant method-dependent differences in TSB results from neonatal samples, consistent with our clinical incident. The differences are largely due to lack of standardisation of calibrator values. This has implications for healthcare resource use and possibly for the neurodevelopment of infants. Intervention is needed at a number of levels, including clinical reporting of incidents arising from discordant results, commitment by manufacturers to ensure metrological traceability of methods with sufficiently low uncertainty in the final measurements, and availability of commutable quality assurance material to monitor assay performance, especially at the clinical decision points for neonatal jaundice.

High incidence of macrotroponin I with a high-sensitivity troponin I assay.

BACKGROUND: Cardiac troponin is the preferred biomarker of myocardial injury. High-sensitivity troponin assays allow measurement of very low levels of troponin with excellent precision. After the introduction of a high-sensitivity troponin I assay the laboratory began to receive enquiries from clinicians about clinically discordant elevated troponin I results. This led to a systematic investigation and characterisation of the cause. METHODS: Routine clinical samples were measured by the Architect High Sensitive Troponin-I (hsTnI) and the VITROS Troponin I ES assays (VitrosTnI). Results that were elevated according to the Architect but not the VITROS assay (Group 1) or results elevated by both assays but disproportionately higher on the Architect (Group 2) were re-analysed for hsTnI after re-centrifugation, multiple dilutions, incubation with heterophilic blocking reagents, polyethylene glycol (PEG) precipitation, and Protein A/G/L treatment. Sephacryl S-300 HR gel filtration chromatography (GFC) was performed on selected specimens. RESULTS: A high molecular weight complex containing immunoreactive troponin I and immunoglobulin (macrotroponin I) was identified in 5% of patients with elevated hsTnI. Patients with both macrotroponin and myocardial injury had higher and longer elevation of hsTnI compared with VitrosTnI with peaks of both macrotroponin and free troponin I-C complex on GFC. CONCLUSIONS: Circulating macrotroponin I (macroTnI) causes elevated hsTnI results with the Architect High Sensitive Troponin-I assay with the potential to be clinically misleading. The assay involved in this investigation may not be the only assay affected by macrotroponin. It is important for laboratories and clinicians to be aware of and develop processes to identify and manage specimens with elevated results due to macrotroponin.

Recovery of drugs of abuse from Dräger DCD5000 oral fluid collection device in Australia.

In Australia, it is a requirement of workplace oral fluid (OF) drugs of abuse testing that drug recovery from collection devices be verified by an accredited laboratory. Recovery data are used in conjunction with collection volume imprecision data and uncertainty of measurement to provide an estimation of drug concentration in neat OF. The manufacturer's product information for the DCD5000 collection device indicates that the collection volume of the swab is 380 µL. Recovery data for the swab when used with the isopropanol provided by the manufacturer are not available. A series of experiments using fortified drug-free OF were performed to assess the collection volume imprecision of the Dräger DCD5000 swab and the recovery of drugs from the swab using isopropanol. The fortified OF was collected with the swabs (n = 16), and swabs were discharged into vials of isopropanol as per the manufacturer's instructions. The mean collection volume of the DCD5000 swab was 487 µL with an imprecision of 1.3%. Recovery of drug from the device ranged from 86 to 98% for drugs listed in the Australian OF workplace testing standard. Recovery of methadone, buprenorphine and norbuprenorphine ranged from 93 to 102%. Recovery of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidene was 45%, suggesting that urine is more suitable sample if methadone therapy is being monitored. Overall, drug recovery from the device using isopropanol was acceptable when the increased collection volume of the swab was taken into account.

LC-MS/MS method for the quantitation of metabolites of eight commonly-used synthetic cannabinoids in human urine--an Australian perspective.

An LC-MS/MS method for the quantitation of urinary metabolites of eight JWH-type synthetic cannabinoids (SCs) has been developed and validated. Urine samples are subjected to deconjugation using ß-glucuronidase, followed by a solvent extraction procedure. Compounds are separated on a reverse-phase HPLC column within a 14 min cycle. Low assay limits are required in order to demonstrate prior exposure to SCs. Matrix effects were studied and proved to be significant for selected analytes, and were challenging to circumvent as isotope-labeled internal standards are not available. An elimination profile from a naïve user following a single smoke of "Kronic" was constructed, showing urinary excretion over 2-3 days with peak concentrations of different metabolites 3-16.5 h after smoking. This method has been developed to process several hundred samples within a high-throughput drugs of abuse laboratory, with growing evidence that the use of synthetic cannabinoid blends is common within the Australian workforce.

Can one point-of-care glucose meter be used for all pediatric and adult hospital patients? Evaluation of three meters, including recently modified test strips.

BACKGROUND: within hospitals, bedside blood glucose measurements are widely used for investigating suspected hyper- or hypoglycemia, monitoring diabetes, and adjusting glucose-lowering medication. Numerous point-of-care glucose meters are available, but for large hospitals using the same meter in all settings has practical and economic advantages. This investigation sought to identify a meter that was accurate, precise, and free from interferences, making it suitable for use across all ages and diseases. METHODS: lithium-heparinized whole blood was analyzed, under various conditions, on the HemoCue Glucose 201 (Hemocue AB, Ängelhom, Sweden), Accu-Chek Performa (Roche Diagnostics, Basel Switzerland) (using the newly reformulated maltose-insensitive strips), and Optium (Abbott Diabetes, Alameda, CA, USA) glucose meters and compared with plasma glucose measurements on the Vitros 5,1 FS analyzer (Ortho Clinical Diagnostics, Neckargemund, Germany). RESULTS: biases of 3.2%, -5.8%, and -8% were found with Accu-Chek, Optium, and HemoCue, respectively. Within-run imprecision was 2.5-5.8%. Between-run imprecision was 3.1-6.8%, with the Accu-Chek performing best. All meters measured to 1.3 mmol/L with acceptable precision (coefficient of variation, <14%). Varying hematocrits between 0.2 and 0.7 L/L affected results of all meters. Interference at clinically relevant concentrations of galactose and possibly maltose was demonstrated with the Accu-Chek. CONCLUSIONS: all three meters are sufficiently accurate and precise for in-hospital use. Because of possible interference by galactosemia or high hematocrit, the Accu-Chek is not the safest option for neonatal use. Patients receiving high doses of maltose in therapeutic infusions may still be at risk of being falsely classified as euglycemic or hyperglycemic with the reformulated Accu-Chek strips, and clinical evaluation of these strips in patients receiving maltose-containing infusions is urgently needed.