Lorna Clark

A practical approach for the validation and clinical implementation of a high-sensitivity cardiac troponin I assay across a North American city ☆ ☆☆

Objectives Despite several publications on the analytical performance of high-sensitivity cardiac troponin (hs-cTn) assays, there has been little information on how laboratories should validate and implement these assays into clinical service. Our study provides a practical approach for the validation and implementation of a hs-cTn assay across a large North American City. Design and methods Validation for the Abbott ARCHITECT hs-cTnI assay (across 5 analyzers) consisted of verification of limit of blank (LoB), precision (i.e., coefficient of variation; CV) testing at the reported limit of detection (LoD) and within and outside the 99th percentile, linearity testing, cTnI versus hs-cTnI patient comparison within and between analyzers (Passing and Bablok and non-parametric analyses). Education, clinical communications, and memorandums were issued in advance to inform all staff across the city as well as a selected reminder the day before live-date to important users. All hospitals switched to the hs-cTnI assay concurrently (the contemporary cTnI assay removed) with laboratory staff instructed to repeat samples previously measured with the contemporary cTnI assay with the hs-cTnI assay only by physician request. Results Across the 5 analyzers and 6 reagent packs the overall LoB was 0.6 ng/L (n=60) with a CV of 33% at an overall mean of 1.2 ng/L (n=60; reported LoD=1.0 ng/L), with linearity demonstrated from 45,005 ng/L to 1.1 ng/L. Precision testing with a normal patient-pool QC material (mean range across 5 analyzers was 3.9–4.4 ng/L) yielded a range of CVs from 7% to 10% (within-run) and CVs from 7% to 18% (between-run) with the high patient-pool QC material (mean range across 5 analyzers was 29.6–36.3 ng/L) yielding a range of CVs from 2% to 5% (within-run) and CVs from 4% to 8% (between-run). There was agreement between hs-cTnI versus cTnI with the patient samples (slope ranges: 0.89–1.03; intercept ranges: 1.9–3.8 ng/L), however, the median CV on patient samples <100 ng/L across the analyzers was 5.6% for hs-cTnI versus 18.7% for the contemporary assay (p<0.001). Following the switch to hs-cTnI testing, no requests for repeat measurements were received. Conclusions Validation and implementation of hs-cTnI testing across multiple sites requires collaboration within the laboratories and between hospital laboratories and clinical staff.

Assessing Pneumatic Tube Systems with Patient-Specific Populations and Laboratory-Derived Criteria

To the Editor:nnThe October 2011 issue of Clinical Chemistry highlights the importance of monitoring pneumatic tube systems (PTSs) to control preanalytical factors that may affect laboratory results (1, 2). Two important themes emerge: ( a ) the possible requirement of more-frequent monitoring if the PTS produces changes in the 3-axis acceleration (i.e., forces) and ( b ) consideration for specific populations of patients (i.e., hematology and/or oncology patients) whose blood samples may be more susceptible to PTS. As Felder noted, the work by Streichert et al. may usher in a new practice for monitoring PTS by means of data loggers (1, 2); however, in the interim, laboratories will be required to monitor PTSs with split-sample testing. In this regard, the number of studies and approaches that have assessed the impact of PTSs on the quality of samples has been surprisingly limited (3). Moreover, the available guidelines have mainly suggested that PTSs be evaluated and that certain analytes may be affected by the automated system (e.g., lactate dehydrogenase), whereas others (e.g., aspartate aminotransferase) may not (4). Additional questions arising from the study of Streichert et al. are whether samples from healthy …

Effect of freeze–thaw and refrigeration conditions on high-sensitivity troponin T concentrations:

In a medical biochemistry laboratory, under ISO 15189:2002, the postexamination process includes the systematic review, formatting and interpretation, authorization for release, reporting of results, transmission of results and storage of samples of the examinations. Results must reach the user in a timely and secure manner. Clause 5.8 of the standard sets out that ‘the laboratory shall establish policies and practices to ensure that results distributed by telephone or other electronic means only reach an authorised receiver’. The CPA (UK) Ltd Standards for the Medical Laboratory 2010 set out the requirements for giving reports by telephone. Among the requirements demanded of the laboratory management are formalized procedures for (a) the circumstances in which reports may be given; (b) the nominated individual who may give reports; and (c) the individuals who may receive reports. In November 2010, the Royal College of Pathologists (RCPath) published a document ‘Out-of-hours reporting of results requiring urgent clinical action to primary care: advice to pathologists and those that work in laboratory medicine’. This was in response to reports of the inability of laboratory staff to find an appropriate primary care physician to act on a markedly abnormal, and sometimes lifethreatening, result outside of conventional working times. The general principle is set out in section 4 of the RCPath document. ‘The responsibility of the laboratory staff is to communicate the markedly abnormal test result to the clinical team – either the GP who made the request or to the out-of-hours provider’. The next statement is naı̈ve. ‘It is the responsibility of the requesting team to review results of tests that they have requested and have proper handover arrangements in place to review and act on abnormal results after hours. The Primary Care Trust (PCT) or commissioning body has a responsibility to ensure that adequate out-of-hours cover arrangements are available, and that details of those arrangements are communicated to the laboratory. PCTs or GP commissioning bodies should be asked to inform the laboratory of specific arrangements for making telephone contact with a GP out of hours.’ It is recognized that the out-of-hours cover doctor will have limited access to patient information. These are clear patient safety issues. The RCPath document does not address the context of independent GPs outside a state system. It downplays the ethical responsibility of the doctor to the individual patient and the parallel role of the consultant chemical pathologist and consultant clinical scientist in patient care. The General Medical Council requires doctors to put the care of a patient as a first concern. Therefore it is the duty of the doctor to provide any laboratory to which patient samples are sent with contact arrangements in the event of a life-threatening or very urgent patient result. The clinical biochemistry laboratory consultant must also place the care of the patient first. All requests to the laboratory are referrals to the consultant. My experience is that locum and out-of-hour services are unsatisfactory means of dealing with dangerous laboratory results. On occasions when an appropriate doctor cannot be contacted, there has often been no information on the address of the patient. Where an appropriate professional cannot be traced but the patient’s address and phone number is available, I have directly contacted the patient. Where an address only is available, I have rarely asked the police to call and arrange for transfer of the patient. I believe that access to the direct personal cell phone number of every requestor of laboratory tests which may require urgent intervention should be incorporated into the governance requirements for clinical laboratory accreditation. Since I instituted this policy in 2010, there have been no cases where the laboratory could not find the relevant GP. A minority of GPs were resistant to providing the information and ultimately 2.5% refused and were asked to go elsewhere. This stipulation should also be a requirement for practice accreditation in primary care and must now be considered a best practice standard when GP practice registration is introduced under the Care Quality Commission in the UK in 2013.

Within-run precision and outlier detection for the Abbott ARCHITECT cardiac troponin I assay

Sawyer et al. assessed the rate of cardiac troponin I (cTnI) outliers on the Abbott ARCHITECT analyzers. Importantly, they focused on the critical region where the difference between the results of duplicate measurements exceeded the allowable difference, with one of the two measurements above the 99th percentile cutoff (50.04 mg/L) and termed this a ‘critical outlier’. Their findings are noteworthy in that the critical outliers appear to be false positives with the root cause unknown but unlikely to be related to an analyzer malfunction. Our laboratory, since November 2012, has used the Abbott ARCHITECT cTnI assay for routine clinical care. In addition to regular commercial quality control (QC) material, we monitor performance using a low cTnI concentration patient-pool QC material (approximately 0.03 mg/L). Recently, our laboratory switched to the 500-test reagent pack from the 100-test reagent pack and through monitoring with the lowpool QC material identified possible positive cTnI outliers at this critical region. After assurances from the manufacturer that the analyzer was functioning appropriately, we set up a series of experiments utilizing a pool of patient samples with ‘normal’ cTnI concentrations to explore the extent of positive outliers and to assess if it was related to a specific analyzer or cTnI reagent lot. Briefly, for experiment 1 we obtained ethylenediaminetetraacetic acid plasma from patient samples that had a reported concentration of 0.02mg/L, pooled the material, and aliquoted in 10 individual cups to be analysed on an 8200 (Site 1) and 16200 (Site 2) analyzer after 60min of instrument inactivity with the same 500-test reagent lot (Lot#17117UN13). The imprecision was doubled on the 8200 as compared with the 16200 analyzer (CV1⁄4 26.6% vs. 13.0%; Table 1, experiment 1), with the contributing factor being the first elevated result. Of note, assessing higher concentration patient pools at Site 1 (midpool mean (n/CV)1⁄4 0.521 mg/L (n1⁄4 9/2.2%), highpool mean (n/CV)1⁄4 5.542 mg/L (n1⁄4 10/2.6%)) using the same 500-test reagent lot, there was no evidence of an elevated first result effect (i.e. highest concentration obtained after first result). To assess if this first result outlier at the low/normal concentration was due to the specific 500-test reagent lot stored at Site 1, experiment 2 was performed using a 100-test reagent lot (Lot#95509UN13) and a 500-test reagent (Lot#17117UN13) obtained from Site 2. Three rounds of testing were performed with both lots of cTnI reagent with at least 20min of inactivity before each round of testing (Table 1, experiment 2). These data demonstrate that the first elevated result was apparent only with the 500and not the 100-test reagent lot at Site 1. Experiment 3 was performed on two additional 500-test reagent lots (Lot#89576UN13 and 23070UN13) versus the 100test reagent lot, and the first elevated result effect was also evident with the different 500-test reagent lots. Sawyer et al. did not indicate whether a 500or 100test reagent lot was used during their study, nor were they able to identify if the critical outlier was with the first result after a period of inactivity. Our experiments suggest that contributing factors to variability include a period of inactivity on the analyzer (i.e. in running mode with no samples being processed) and the reagent pack size. During our investigation, at no time did we observe differences 50.03mg/L with the normal pool that may have been misinterpreted clinically as a significant change. We were able to uncover this positive first result outlier only with a normal cTnI patient-pool, thus reaffirming the importance of monitoring cTnI assays with appropriate QC material below the 99th percentile, regardless of using a high-sensitivity or sensitive assay. Finally, our findings indicate a renewed importance of performing within-run precision testing when evaluating cTnI reagent lots.

Assessment of a four hour delay for urine samples stored without preservatives at room temperature for urinalysis.

OBJECTIVESnTo determine whether urine storage at room temperature for up to 2h versus 4h changes urinalysis results.nnnDESIGN AND METHODSnWe compared the rejection rate at eight different hospital laboratories and concordance of urinalysis results (n=83; two laboratories) between urines analyzed within 2h and 4h after collection.nnnRESULTSnThe rejection rate at the two hour cutoff was significantly higher as compared to the four hour cutoff. The concordance between urinalysis results was 97-100% between the two and four hour analyses.nnnCONCLUSIONnUrine may be stored for up to 4h at room temperature without significant changes to the urinalysis results.

Assessing matrix, interferences and comparability between the Abbott Diagnostics and the Beckman Coulter high-sensitivity cardiac troponin I assays

Abstract Background: Analytical evaluation of high-sensitivity cardiac troponin (hs-cTn) assays, with particular attention to imprecision, interferences and matrix effects, at normal cTn concentrations, is of utmost importance as many different clinical algorithms use concentration cutoffs <10 ng/L for decision-making. The objective for the present analytical study was to compare the new Beckman Coulter hs-cTnI assay (Access hsTnI) to Abbott’s hs-cTnI assay in different matrices and for different interferences, with a focus on concentrations <10 ng/L. Methods: The limit of blank (LoB) and the limit of detection (LoD) were determined in different matrices for the Beckman hs-cTnI assay. Passing-Bablok regression and difference plots were determined for 200 matched lithium heparin and EDTA plasma samples for the Beckman assay and 200 lithium heparin samples for the Abbott assay. Both EDTA and heparin plasma samples were also evaluated for stability under refrigerated conditions, for endogenous alkaline phosphatase interference and for hemolysis and icterus. Results: The Beckman hs-cTnI assay LoB was 0.5 ng/L with the following range of LoDs=0.8–1.2 ng/L, with EDTA plasma yielding lower concentrations as compared to lithium heparin plasma (mean difference=−14.9%; 95% CI=−16.9 to 12.9). Below 10 ng/L, lithium heparin cTnI results from the Beckman assay were on average 1.1 ng/L (95% CI=0.7 to 1.5) higher than the Abbott results, with no difference between the methods when using EDTA plasma (mean difference =−0.1 ng/L; 95% CI=−0.3 to 0.2). Low cTnI concentrations were less effected by interferences in EDTA plasma. Conclusions: The Access hsTnI method can reliably detect normal cTnI concentrations with both lithium heparin and EDTA plasma being suitable matrices.

The potential role of a turbidimetric heart-type fatty acid-binding protein assay to aid in the interpretation of persistently elevated, non-changing, cardiac troponin I concentrations

BACKGROUNDnElevated and non-changing high-sensitivity cardiac troponin (hs-cTn) concentrations may suggest a process other than acute injury, possibly due to chronic condition(s) causing the elevation, an analytical error/interference or the formation of macrocomplexes. Heart-type fatty acid binding protein (H-FABP) might be useful in this setting to identify the etiology of abnormally high and non-changing cTn concentrations which could aid clinical decision making in the hospital setting.nnnMETHODSnWe analytically validated the H-FABP assay (Randox) on the Abbott ARICHTECTc8000 platform, testing imprecision, linearity, stability, and matrix comparison. Over the 2-month analytical validation; EDTA plasma samples from patients with a hospital visit with persistently elevated and stable cTnI concentrations (Abbott hs-cTnI≥52u202fng/L or 2x99th percentile upper limit of normal (ULNu202f=u202f26u202fng/L) with change between results <20%) were collected and frozen (-20u202f°C). These samples were tested with the H-FABP assay, polyethylene glycol (PEG) precipitation, with the lowest estimated glomerular filtration rate (eGRF) during the hospital visit also obtained from these patients.nnnRESULTSnThe H-FABP assay was linear, with concentrations stable after 4u202ffreeze/thawu202fcycles, up to 150u202fh at room temperature, and comparable between lithium heparin and EDTA plasma. During the validation there were 6 patients with eGFR ≥60u202fml/min/1.73m2 identified (total population screened nu202f=u202f917) with high and non-changing hs-cTnI concentrations. All 6 patients had H-FABP<2xULN; with 3 patients having a macrocomplex and a final diagnosis of not ACS.nnnCONCLUSIONnTesting of H-FABP in patients with an eGFR≥60u202fml/min/1.73m2 with persistently high and stable cTn elevations may help to confirm prior cardiac injury or the presence of macrocomplexes as the source of these elevations.