Sonia L. La'ulu

Performance characteristics of the ARCHITECT Galectin-3 assay.

OBJECTIVESnGalectin-3 is an emerging biomarker that is commonly increased in patients with heart failure and/or patients at risk for cardiovascular disease. We evaluated the Galectin-3 assay on the Abbott ARCHITECT i1000(SR) and ARCHITECT i2000(SR) at 2 testing sites.nnnDESIGN AND METHODSnImprecision (%CV), interference, limits of blank (LoB), detection (LoD), and quantitation (LoQ), linearity, method comparison to an ELISA method, comparisons between plasma and serum, and reference intervals were evaluated. Imprecision was performed based on two runs of duplicate testing conducted daily. Verification of LoB, LoD, and LoQ was performed according to Clinical and Laboratory Standards Institute guidelines. Linearity was evaluated by making 5 dilutions of a high patient EDTA plasma pool with a low patient pool. Reference intervals were established using EDTA plasma collected from self-reported healthy volunteers. A second lot of reagent was used at one site for method comparison and imprecision studies.nnnRESULTSnTotal CVs were ≤6.0%. A positive interference was observed for hemolyzed samples over 2.0 g/L hemolysate. The LoB ranged from 0.1 to 0.3 ng/mL, the LoD from 1.4 to 2.1 ng/mL and the LoQ from 3.0 to 3.3 ng/mL. Linearity studies had slopes and correlation coefficients equal to 1.0. Comparison of the i1000(SR) and i2000(SR) to the ELISA method demonstrated slopes of 1.0 to 1.2 and correlation coefficients of 0.93 to 0.97. The 97.5th percentile of the reference interval was 18.7 and 17.9 ng/mL for the i1000(SR) and i2000(SR), respectively.nnnCONCLUSIONSnThe Abbott Galectin-3 assay demonstrated acceptable analytical performance on both the ARCHITECT i1000(SR) and ARCHITECT i2000(SR).

Ethnic Differences in First-Trimester Thyroid Reference Intervals

To the Editor:nnThyroid disease is common in women of reproductive age, and the physiological changes that occur during pregnancy complicate the diagnosis of thyroid dysfunction. Trimester- and method-specific reference intervals (RIs)1 for thyroid function tests (TFTs) are necessary and should be determined with thyroid autoantibody–negative individuals (1). Ethnic differences in TFT results exist among nonpregnant individuals, but the data on ethnic differences in thyroid function during pregnancy are limited (2–5). We used the Abbott ARCHITECT i 2000SR analyzer to determine RIs for TFTs by ethnic group for the first trimester of pregnancy.nnSerum samples submitted between 10 and 13 weeks gestation were collected in the US from 540 Asians, 549 blacks, 601 Hispanics, and 878 whites (age, 15–46 years). Gestational ages were provided by the ordering physicians. Iodine status and medical histories were unknown, and only 1 sample was available from each individual. This study was approved by the University of Utah Institutional Review Board. The numbers of thyroid autoantibody–negative individuals were 174, 579, 798, and 626 for gestational weeks 10, 11, 12, and 13, respectively. Samples from 129 self-reported healthy, nonpregnant adult individuals were obtained from 5 Asians, 2 blacks, 2 Hispanics, 114 whites, and 6 individuals of other ethnic backgrounds (63 females and 66 males, 18–62 years of age). Samples were thawed, mixed, centrifuged at 2095 g for 10 min, and …

Method specific second-trimester reference intervals for thyroid-stimulating hormone and free thyroxine.

OBJECTIVEnTo determine second trimester reference intervals for TSH and FT4.nnnDESIGNnSamples from 3102 subjects were tested for TPO and Tg antibodies.nnnMETHODSnElecsys E170 reference intervals for TSH and FT4 were determined using antibody-negative samples.nnnRESULTSnSecond trimester reference intervals for TSH and FT4 were 0.18-4.07 mIU/L and 9.5-15.8 pmol/L, respectively. The Elecsys E170 TSH results were positively biased compared to ARCHITECT i2000(SR) results for these same samples.nnnCONCLUSIONSnMethod-specific reference intervals are required for TSH and FT4.

Performance characteristics of five cardiac Troponin I assays

BACKGROUNDnThe aim of this study was to evaluate the performance characteristics of cardiac Troponin I (cTnI) assays on the Access 2, Advia Centaur, Architect i1000(SR), Architect i2000(SR), and Vitros ECi analyzers.nnnMETHODSnTo determine the 99th percentile, plasma and serum samples were drawn from 400 apparently healthy subjects. Functional sensitivity was evaluated by testing 10 panels of serum pools in duplicate for 10days using 2 reagent lots. Imprecision was also assessed using commercial quality control materials. For method comparison, 100 plasma samples were tested by all methods with the Architect i2000(SR) assay as the comparison method.nnnRESULTSnThe 99th percentile ranged from 0.013 to 0.020microg/l. Calculated CVs at the 99th percentile were 23-52%. cTnI concentrations at a 10% CV ranged from 0.039 to 0.101microg/l. Total CVs determined using quality control materials were 2.4-10.0%. Method comparison results by Deming regression had slopes of 1.03-1.51. The mean bias for cTnI samples between 0.01 and 1.0microg/l ranged from 0 to 0.2microg/l.nnnCONCLUSIONSnNo method demonstrated a concentration with a 10% CV that was less than the 99th percentile for healthy adults. All methods compare well to the Architect i2000(SR) assay with the Advia Centaur having the highest positive bias.

The Osmolal Gap: What Has Changed?

To the Editor:nnThe osmolal gap (OG)1 is calculated in the emergency department (ED) when ingestion of ethylene glycol, methanol, isopropyl alcohol, acetone, or other osmotically active substances are suspected. Serum osmolality is measured and also calculated with the variables serum glucose, sodium, and blood urea nitrogen (BUN) concentrations. The difference between the measured and calculated osmolality is defined as the OG. Boyle et al. (1) recently cautioned against using the OG as a screening tool for toxic-alcohol poisoning. One reason relates to the debate about what constitutes a normal OG and the variations in the range of osmolal gaps (2). To address what constitutes a normal OG, we determined the OG range for healthy subjects and examined data from hospitalized patients by use of several published equations for calculating serum osmolality.nnAfter obtaining informed consent, we collected blood from 126 self-reported healthy subjects. The serum osmolality glucose, potassium, sodium, and BUN were within respective reference intervals (Tables 1 and 2). The OG log-transformed parametric reference intervals (central95%) were −8 to 11 mOsm/kg and 3 to 22 mOsm/kg by use of Eqs. 1 and 2, respectively.nnView this table:nnTable 1. Reference intervals of measured analytes.nnView this table:nnTable 2. Osmolal gaps and osmolality for healthy and ED patients in 1998 and 2007–2009.nnGeneral equation (2,4)nn Osm = 2 ( Na + ) + Glucose 18 + BUN 2.8 + EtOH 4.6 (1)nGlaser (3) and Krahn and Khajuria [4; see Dorwarts equation] Osm = 1.86 ( Na + ) + Glucose 18 + BUN 2.8 + EtOH 4.6 + 9 (2)nnRasouli and Kalantari (5) Osm = 1.897 ( Na + ) + Glucose 18 + BUN 2.8 + EtOH 4.6 + 13.5 (3)nnKrahn and Khajuria (4) Osm = 1.86 ( Na + + K + ) + 1.15 ( Glucose 18 ) + BUN 2.8 + 1.2 ( EtOH 4.6 ) + 14 (4) Osm = 2 ( Na + ) + 1.15 ( Glucose 18 ) + BUN 2.8 + 1.2 ( EtOH 4.6 ) (5)nnED records identified 157 patients in 1998 and 117 patients in 2007–2009 …

Performance characteristics of the Architect brain natriuretic peptide (BNP) assay: a two site study.

INTRODUCTIONnBrain natriuretic peptide (BNP) is produced by the ventricles of the heart and is a biomarker for heart failure. Several commercial assays are now available. We evaluated the performance characteristics of the ARCHITECT BNP assay.nnnMETHODSnWe evaluated the limit of blank, limit of detection, linearity and imprecision. Method comparison studies were performed with 3 other automated BNP assays including the ADVIA Centaur, AxSYM, and UniCel DxI 800 methods.nnnRESULTSnThe mean LOB and LOD of the Architect assay were 3.5 and 5.8 ng/L, respectively. Imprecision studies yielded within run CVs of 1.1 to 5.1% and total CVs of 2.3 to 5.3% using human plasma based multi-constituent controls at concentrations of 92, 500, and 3500 ng/L. The maximum deviation from the target recovery for dilution linearity was 9.6%. Concordance with other BNP assays at a 100 ng/l cutoff was 91 to 98% and kappa statistics were 0.78 to 0.96. The mean difference between the Architect and Advia Centaur methods was positive. For the other methods, the mean difference with the Architect was negative.nnnCONCLUSIONSnThe Architect BNP assay shows good performance characteristics with total imprecision < or =5.3%. It agrees well with the Advia Centaur, AxSYM, and UniCel DxI BNP assays.

Detection of macro-creatine kinase and macroamylase by polyethylene glycol precipitation and ultrafiltration methods.

BACKGROUNDnMacroenzymes may cause elevations in serum enzyme activity. Macroenzymes are not common; however their detection is important because they cause diagnostic confusion and therapeutic errors.nnnMETHODSnWe analyzed 2 of the most prevalent macroenzymes in the literature, macro-creatine kinase (macro-CK) and macroamylase, using 2 methods for detection, polyethylene glycol (PEG) precipitation and ultrafiltration (UF). Enzyme measurements were made using a Roche Modular Analytics P analyzer. Imprecision was assessed using quality control material. We evaluated 125 samples from apparently healthy subjects to establish reference intervals. For macro-CK comparison, 94 samples with activities >200 U/l were analyzed with both PEG precipitation and UF and compared to electrophoresis. PEG precipitation and UF were compared for macroamylase detection using 130 samples with amylase activities >110 U/l.nnnRESULTSnUF was more precise and demonstrated narrower reference intervals for both analytes. PEG precipitation and UF were able to detect true cases of macro-CK with overall agreement with electrophoresis of 79.8% and 80.9%, respectively. Both methods detected the same number of positive macroamylase samples; however PEG precipitation resulted in a greater number of indeterminate cases.nnnCONCLUSIONnThis is the first report where UF has been shown useful for the detection of both macro-CK and macroamylase.

Performance characteristics of the AxSYM D-dimer assay

BACKGROUNDnD-dimer testing is used to exclude thromboembolic disease in outpatients suspected of having deep venous thrombosis and pulmonary embolism.nnnMETHODSnWe evaluated 4 D-dimer assays for imprecision and method comparison and evaluated the AxSYM method for interference, linearity, and reference interval. Method comparison testing was performed using the following methods: Abbott AxSYM, bioMérieux mini VIDAS, Diagnostica Stago STA Compact, and Biosite Triage Meter Plus.nnnRESULTSnTotal CVs for all methods ranged from 3.7% for the STA Compact to 17.3% for the Triage Meter. The AxSYM showed good agreement with the other methods with slopes ranging from 1.17 to 1.22 by Passing-Bablok regression and correlation coefficients >or=0.96. Interference from hemolysis, icterus, and lipemia had <7% deviation from the intended D-dimer concentration. Linearity had <or=11.5% deviation from target values.nnnCONCLUSIONSnThe AxSYM D-dimer assay provides a precise, rapid, and user-friendly method for D-dimer testing with good correlation to other methods.

Ordering of the Serum Angiotensin-Converting Enzyme Test in Patients Receiving Angiotensin-Converting Enzyme Inhibitor Therapy: An Avoidable but Common Error

BACKGROUNDnSerum angiotensin-converting enzyme (ACE) levels may be decreased by use of ACE inhibitor (ACEI) medication. In this study, we determined how often ACE levels were measured in patients receiving ACEI therapy.nnnMETHODSnACE levels analyzed over a 54-month preintervention time period at an academic medical center were reviewed retrospectively for tests performed during ACEI therapy. These data were compared with a large, deidentified dataset of ACE levels measured at a national reference laboratory; in vitro studies of ACEI inhibition; and liquid chromatography time-of-flight mass spectrometry detection of lisinopril in a subset of clinical specimens.nnnRESULTSnOver a 54-month period, 1,292 patients had ACE levels measured, with 108 patients (8.4%) receiving ACEI therapy at the time of testing. ACE levels measured for patients receiving ACEI therapy were substantially lower. In general, clinical teams did not recognize a medication effect on ACE levels. Introduction of a warning prompt in the electronic health record reduced the ordering of ACE levels in patients receiving ACEIs by > 60% in a 17-month postintervention time period. The deidentified dataset of ACE levels at a reference laboratory showed a bimodal distribution, with a peak of very low ACE levels. Using liquid chromatography time-of-flight mass spectrometry, the presence of lisinopril was confirmed in a subset of specimens with low ACE activity. In vitro studies of two different ACE assays showed significant inhibition of activity at clinically relevant concentrations.nnnCONCLUSIONSnAssessment of ACE activity is often measured for patients receiving ACEIs, potentially leading to low ACE concentrations and inaccurate interpretations.

Thrombin-mediated degradation of parathyroid hormone in serum tubes

BACKGROUNDnIntact parathyroid hormone (PTH) tests are frequently sandwich immunoassays. Enzymes that cleave PTH may cause falsely lower PTH results. The objective of this study was to determine whether bovine thrombin in Becton Dickinson (BD) Vacutainer rapid serum tubes™ (RSTs) may lead to PTH results that are lower than in plasma separator tube™ (PST) or serum separator tube™ (SST) collections.nnnMETHODSnTubes of blood (PST, SST, and RST) were collected from donors. PTH concentrations were measured on a Roche Cobas e602 analyzer in aliquots held at room temperature or 4°C across time. Instrument comparison studies were also conducted on an Abbott Architect i1000SR and a Siemens Immulite 2000 XPi. Previously collected serum specimens were also incubated in exogenous bovine thrombin, the direct thrombin inhibitor hirudin, or both. Freshly collected RST specimens were also spiked with hirudin after clotting and centrifugation.nnnRESULTSnSignificant decreases in PTH degradation rate constants were observed according to tube type, with degradation rates faster in RSTs than SSTs, and SSTs faster than PSTs. PTH degradation rate was temperature dependent. PTH decreases induced by exogenous bovine thrombin, as well as endogenous human thrombin, were reduced by hirudin.nnnCONCLUSIONSnBovine thrombin is responsible for the decrease in PTH results observed in RSTs. Endogenous human thrombin, activated during clot formation, is likely responsible for the smaller decreases observed in non-RST sera versus plasma.