Brock Jones

Lipaemic samples: effective process for lipid reduction using high speed centrifugation compared with ultracentrifugation.

INTRODUCTION Reducing laboratory errors and improving patient safety is receiving a lot of attention. Lipaemic samples are cause of analytical errors and present challenges for laboratories, particularly for those without ultracentrifuges. Lipaemia can originate from physiological (postprandial metabolism), para-physiological causes (e.g. IV administration of lipids) as well as metabolic disturbances (e.g. hypertriglyceridaemia). MATERIALS AND METHODS We have evaluated a procedure with 10 native lipaemic sample pools (triglyceride concentration range 11.6-42.7 mmol/L) for the ability to reduce lipid concentration using a high speed micro-centrifuge (double centrifuged at 21.885 x g for 15 min) compared with an ultracentrifuge, and provide accurate results. Results of sodium, creatinine, urate, total protein, lactate dehydrogenase (LD), magnesium and, cholesterol and triglyceride analysis on a Beckman DxC800 analyser are presented. RESULTS Data from our tertiary level hospital showed approximately 0.7% of the samples received for lipid studies have triglyceride levels > 10 mmol/L which can potentially cause analytical interference. The mean differences from the neat aliquot to the ultracentrifuged and high speed centrifuged sample pools were: cholesterol 4.9 mmol/L and 3.1 mmol/L; and triglycerides 17.4 mmol/L and 15.0 mmol/L respectively. The data confirms high speed centrifugation is almost as effective as ultracentrifugation in lipid reduction. CONCLUSION The procedure utilized in this study using a high speed micro-centrifuge showed it is effective in reducing lipid levels and provides a suitable alternative to ultracentrifuged samples to provide accurate results.

Glucose meters: evaluation of the new formulation measuring strips from Roche (Accu-Chek) and Abbott (MediSense):

Background Both Roche and Abbott have released new glucose meter strips. They supply the entire Australian hospital market. The present study compared the performance of the new strips utilizing various specimen types (capillary, venous lithium heparin whole blood, venous lithium heparin plasma and serum) and evaluated how well they comply with the International Standards Organization (ISO) 15197 criteria. Methods The study included imprecision, patient comparison and interference studies. Participants with and without diabetes were recruited to evaluate the performance of various specimen types against the Beckman DxC800 glucose method. The strips were tested for different interferences: galactose, maltose, lactose, Icodextrin, Intragam, paracetamol, sodium, ascorbic acid, variable strip storage temperature, haematocrit, haemolysis and lipaemia. Results The imprecision of the two strips was ∼5% or less, except for the Abbott strip at very low values (1.4 mmol/L), ∼7%. In total, 78% and 84%, respectively, of the results from the finger prick capillary specimens with the Roche (Accu-Chek Performa meter) and Abbott (Optium Xceed meter) strips, not 95% or greater as recommended by the ISO guideline, were within the recommended limits compared with reference plasma estimation on laboratory analysers. Galactose, ascorbic acid, haematocrit and sodium on the Roche and ascorbic acid and haematocrit on the Abbott strip continue to interfere to a variable degree with the glucose measurement. Conclusion Analytically small differences exist between the glucose meter strips. The most significant analytical difference with the strips was at low glucose levels when compared with laboratory analyses and this may be of clinical importance. The impact of some of the interferences is variable between the two strips. Individuals, health-care professionals and health-care institutions should consider these data when selecting glucose meters for the management of people with diabetes mellitus.

Extent of bilirubin interference with Beckman creatinine methods

Abstract Background The aim of the study was to determine the extent of bilirubin interference on two different Beckman–Coulter creatinine methods used on the CX5 PRO/DxC 600 and the DxC 800 systems, respectively. Methods The Beckman methods were compared with a high-performance liquid chromatography (HPLC) method using 104 patient samples with creatinine concentrations <133 μmol/L and bilirubin concentrations of between 30 and 802 μmol/L. Results The linear regression analysis calculations expressing the relationship between bilirubin concentration and the observed difference between the Beckman and HPLC creatinine methods are: DxC800 creatinine M (modular or cup) method: r 2 0.217, slope −0.023 and intercept 6.43; and DxC600 method: r 2 0.7324, slope −0.0882 and intercept 12.01. Conclusions There is significantly greater interference by bilirubin on the CX5 PRO/DxC 600 method, which can lead to inaccuracy in the calculation of the estimated glomerular filtration rate by the Modification of Diet in Renal Disease equation.

Which point-of-care creatinine analyser for radiology: direct comparison of the i-Stat and StatStrip creatinine methods with different sample types

Background Availability of whole blood creatinine estimation for patients scheduled to undergo radiological contrast investigations can provide information to aid patient care by reducing adverse effects and improving departmental efficiencies. Methods We performed imprecision studies, different patient sample type comparison in 40 participants, and a limited interference study with dopamine and dobutamine on the i-Stat and StatStrip point-of-care enzymatic analysers with the Beckman DxC800 Jaffe assay. Results Imprecision results showed that the i-Stat performed better. Patient comparison data indicated that the i-Stat provided better correlation than the StatStrip for all the different sample types with correlation coefficients (r2) being 0.995-0.996 and 0.918-0.995, respectively. The i-Stat results had a small positive bias of 6-9% for the three different sample types, which required different reference intervals. The StatStrip method showed greater scatter and overall small negative bias of 26% for the whole blood samples and a 10% positive bias with the plasma samples. Dopamine caused significant positive interference with the i-Stat only while dobutamine caused a small negative bias with the StatStrip method only. Conclusions The findings indicated there are differences offered by the two systems. The StatStrip requires a very small finger prick capillary sample, calculates estimation of the glomerular filtration rate and has an adjustment option to improve correlation with the local method. The i-Stat offers better analytical imprecision and patient comparison with the laboratory method with the three sample types but showed significant interference from dopamine. A final consideration was the availability of middleware to capture patient results with the i-Stat. Based on all the study data, the i-Stat was recommended.

Digoxin overdose - an accurate method for determining free digoxin concentrations on general chemistry analysers post DigiFab treatment

To the Editor,A 58-year-old female presented post overdose of an unknown amount of digoxin 62.5 µg tablets. A level taken 6 h post ingestion was 10 µg/L (therapeutic range 0.8–2.0 µg/L). The patient was bradycardiac 36/min, and was administered five vials of DigiFab (DigiFab, Pherba, Sydney, NSW, Australia). Our digoxin method, Beckman Coulter on the DxC800 general chemistry ana-lyser (Beckman Coulter, Brea, CA, USA) is not suitable for digoxin estimation in the presence of DigiFab due to posi-tive interference.Digoxin continues to be prescribed for the treatment of cardiac disorders, most frequently atrial fibrillation [1]. Digoxin toxicity usually occurs in the context of renal impairment, but as in our case, can be due to deliberate overdose [2]. Additionally related compounds digitoxin, oleander, Chinese herbal medicines (Chan Su, Lu-Shen-wan), spironolactone, etc can contribute or independently produce digoxin toxicity [3]. It is estimated in the USA that 0.4% of all hospital admissions, 1.1% of outpatients and 10%–18% of nursing care residents suffer digoxin toxicity and this is on the decrease [2]. Digibind digoxin-specific antibodies or antidigoxin Fab fragments DigiFab (of ovine origin) are available for life threatening symptoms of severe toxicity. Recommendation for use of both antidotes is identical. Once these antidotes are administered it can be difficult to obtain accurate free digoxin concentrations on a large number of general chemistry or immunoassay analysers. McMillan et al. evaluated 13 methods designed to quantify free digoxin and reported 4/13 showed marked positive interference, 5/13 showed moderate and four methods showed minimal interference [4]. Removing the effect of digoxin Fab fragments can aid decisions regard-ing additional dosing, as well as determining the correct time to recommence digoxin therapy. Manufacturers method inserts indicate that routine methods are not suit -able for digoxin estimation when Digibind is used. Ultra-filtration of the sample to remove the Digibind or DigiFab is a method for eliminating interference. However, ultra-filtration methods are not standardised and may require matrix-specific calibrators and lengthen turn-around-times [4].Here we describe a protein precipitation method that will provide accurate free digoxin concentrations in the presence of the antidotes. Polyethylene glycol (PEG) is non-denaturing water soluble polymer that precipitates proteins [5]. This permits proteins and bound compounds to be removed, providing a supernatant of unbound com-pounds. To determine if this method is suitable for meas-uring free digoxin post DigiFab administration, samples were treated with PEG to remove the DigiFab and its bound digoxin, specifically to DigiFab. PEG concentration was 24 g/100 mL (Fluka#812160, polyethylene glycol 6000, Sigma Aldrich). Samples were mixed with equal volumes of the PEG solution (0.5 mL:0.5 mL), vortex mixed, than centrifuged (5 min, 3000

Interference from Rose Bengal with Total Bilirubin Measurement

We report an unusual cause for a false-positive interference in the total bilirubin method on the Beckman Coulter DxC 800 analyzer and for the hemolytic index (HI) measured on the Roche Modular D. A total bilirubin result of 53 μmol/L was obtained for a patient who had an earlier result of 7 μmol/L on the DxC 800 analyzer. The direct bilirubin concentration remained at <4 μmol/L, and no other results changed in subsequent multibiochemical profiles. The sample had a red/pink tinge. There was no clinical explanation for the increased bilirubin value. A sample obtained the next day had a total bilirubin result of 7 μmol/L. The patient was a participant in a trial for the treatment of severe melanoma lesions with PV-10 [100 mmol/L rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodo-fluorescein disodium; MW, 1017.65 Da) in 9 g/L NaCl (i.e., 10% rose bengal disodium in 9 g/L NaCl); Provectus Pharmaceuticals]. PV-10 causes tumor necrosis, possibly owing to the release of cathepsins (1). The trial protocol is to inject PV-10 directly into the lesion and to collect a blood sample within an hour. The sample in question was collected 20 min after the injection. …

Is the new Beckman AccuTnI+3 assay capable of producing false-positive troponin I results?

Problems with the Beckman AccuTnI assay (Beckman Coulter, Brea, CA, USA) are well documented, specifically false-positive results, which are predominantly due to the lack of robustness of the wash process [1, 2]. Our review of results from the last 2.5 years shows that significantly or immediately medically actionable false-positive results occur at a frequency of 1/600 samples. This is a decrease from when we originally implemented the assay, which is a result of improvements in laboratory sample-handling processes and Beckman technical upgrades on the analyzers. Such inappropriate results have caused laboratories to adopt workarounds, which include running specimens in duplicate by the reflex function [2] to minimize error rate, potential profound clinical implications for patients, and negative impact on the laboratory, health-care providers, and Beckman. The release of the new formulation, AccuTnI+3, has been awaited. It has an improved low-end analytical performance, with a 10% CV at 0.018 μg/L [95% confidence interval (CI) 8–25], 99th percentile of 0.022 μg/L (95% CI 0.011–0.034), and limit of detection (LoD) of 0.012 μg/L [3]. This study also shows that the measurable values between the LoD and the 99th percentile were found on 62% of samples [3]. However, whether the robustness of the assay has improved as a result of the altered mixing and probe wash process changes has not been evaluated [3]. In our experience, specimen quality and wash robustness are the primary causes of the artifactual cardiac troponin I (cTnI) results. The artifactual results occur in both serum and lithium heparin plasma [4]. Hence, we wanted to test the effects of insoluble fibrin and carryover effects actively based on our previously published protocols [1, 2]. This time, both the Access 2 and the DxI800 analyzers were evaluated using the exact same specimens. These experiments were conducted without running any other specimens at the same time-frame on the analyzers. To test the DxI800 analyzer effectively, analysis of the specimens was performed using only a single pipettor, disabling the other three pipettors. This was to simplify the assessment of the effectiveness of the wash processes of the pipettor. The project was approved by the Princess Alexandra Hospital Ethics Committee. Carryover was performed using four different concentrations of cTnI encountered in patient specimens (Table 1). A low TnI concentration pool collected in Greiner serum tubes (Cat No. 456078; Geiner Bio-One, Kremsmünster, Austria) was prepared from fresh serum specimens in the 99th percentile range stated by Moretti et al. [3]. The order of analysis was the same as previously published, that is, duplicate analysis of the low-quality control, triplicate analysis of the pool, singlicate analysis of the high sample, triplicate analysis of the low pool, and duplicate analysis of the low-quality control. The target mean ± standard deviation used for the quality control was 0.036 ± 0.004 μg/L for the Access 2 analyzer and 0.042 ± 0.004 μg/L for the DxI800 analyzer. The difference of approximately 17% in the means suggests that if the same 99th percentile is adopted, there will be differences in the classification and treatment of patients, which additionally may present confusion should results be used interchangeably between the two analyzers in a single episode. The upper linearity limit for the AccuTnI+3 assay is set by Beckman at 95 and 74 μg/L for Access 2 and DxI800, respectively. Samples above these concentrations were diluted to provide the results. The carryover study results *Corresponding author: Dr Goce Dimeski, Chemical Pathology, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, Brisbane, QLD 4102, Australia, Phone: +61 7 3176 2290, Fax: +61 7 3176 7070, E-mail: goce.dimeski@health.qld.gov.au Melanie Coogan, Brock Jones and Nigel Brown: Pathology Queensland, Chemical Pathology, Princess Alexandra Hospital, Brisbane, QLD, Australia

Diagnostic problem caused by an atypical creatine kinase isoenzyme in a patient with myocardial infarction

&NA; This report describes the diagnostic problem caused by an atypical immunoglobulin‐bound creatine kinase isoenzyme in a patient who had a myocardial infarction. In the presence of this atypical isoenzyme, creatine kinase isoenzyme electrophoresis was of no help in determining whether myocardial infarction had occurred. A diagnosis of myocardial infarction was confirmed by carrying out lactate dehydrogenase isoenzyme electrophoresis and finding the characteristic increase in LD1/LD2 ratio and by following the total creatine kinase, aspartate aminotransferase and lactate dehydrogenase activities over a 5‐day period. Further investigations were carried out which characterized the atypical isoenzyme as an uncommon type: creatine kinase‐BB bound to immunoglobulin A lambda.