CoaguChek and Coag-Sense PT2 Meter Point of Care INR Device Validation

OBJECTIVE

To standardize international normalized ratio (INR) measurements and improve data integrity by enabling electronic result transmission for warfarin monitoring, two point-of-care (POC) devices were evaluated against an internal plasma INR reference method.

METHODS

A multicenter study was pursued (January 24, 2022, through October 19, 2022) to compare concordance of two commercially available POC devices, Coag-Sense PT2 Meter (Coag-Sense) and CoaguChek XS Pro and Plus devices (CoaguChek), against an internal plasma INR method among patients treated with warfarin. Bias and linear regression analysis were assessed for these devices including dosing decision accuracy compared with plasma INR reference.

RESULTS

Two hundred ninety-nine patients treated with warfarin across three Mayo Clinic sites agreed to participate. Atrial fibrillation (n=191, 63.9%), venous thromboembolism (n=65; 21.7%), and heart valve prosthesis (n=46; 15.4%) were common anticoagulant indications with a 2.5 INR target for 280 (93.6%) of patients. For the CoaguChek devices, 243 (81.3%) of values fell within 0.2 INR units with plasma INR referent and 285 (95.3%) within 0.4 units (R2=0.93). For the Coag-Sense device, 102 (34.1%) of values fell within 0.2 INR units and 180 (60.2%) within 0.4 INR units of plasma INR values, (R2=0.83; P<.0001). Using the plasma INR as the gold standard, appropriate dosing recommendations would have occurred for 292 (97.7%) of the CoaguChek and 244 (81.6%) of the Coag-Sense results.

CONCLUSION

Compared with a plasma referent, INR values obtained from the CoaguChek devices exhibited less systematic bias compared with Coag-Sense measures. This translates to a greater percentage of concordant management decisions between POC and laboratory INR methods.

SARS-CoV-2 emergency use authorization published sensitivity differences do not correlate with positivity rate in a hospital/reference laboratory setting

During the first year of the COVID-19 pandemic skyrocketing demand for testing in the United States, coupled with supply chain issues, necessitated the use of multiple SARS-CoV-2 molecular testing platforms at many health centers. At our institution these platforms consisted of 8 ordered services for sample triage, using 9 emergency use authorized (EUA) SARS-CoV-2 RNA nucleic acid amplification tests resulting in 10 possible ordered service/EAU combinations. Here we review the results of the first ∼2.9 million samples tested and note the variability in positivity rates. We conclude that differences in reported limit of detection did not translate to differences in positivity rate or show correlation to discordant results observed. This highlights the importance of balancing patient testing capacity needs with the desire to have more sensitive tests.

Evaluation of the analytical sensitivity of ACON and LumiraDx SARS-CoV-2 rapid antigen tests using samples with presumed Omicron variant

BACKGROUND

Analytical sensitivity of 2 rapid antigen tests was evaluated for detection of presumed SARS-CoV-2 Omicron variants and earlier variants of concern.

METHODS

A total of 152 SARS-CoV-2 RNA positive samples (N and ORF1ab positive but S gene negative) were tested for SARS-CoV-2 antigen by ACON lateral flow and LumiraDx fluorescence immunoassays. Sensitivity within 3 viral load ranges was compared among these 152 samples and 194 similarly characterized samples collected prior to the circulation of the Delta variant (pre-Delta).

RESULTS

Antigen was detected in >95% of pre-Delta and presumed Omicron samples for both tests at viral loads >500,000 copies/mL, and 65 to 85% of samples with 50,000-500,000 copies/mL. At viral load <50,000 copies/mL, antigen tests showed better sensitivity in detecting pre-Delta compared to Omicron variants. LumiraDx was more sensitive than ACON at low viral load.

CONCLUSIONS

Antigen tests had decreased sensitivity for detecting presumed Omicron compared to pre-Delta variants at low viral load.

Authorized SARS-CoV-2 molecular methods show wide variability in the limit of detection

On February 29th, 2020, the U.S. Food and Drug Administration issued the first Emergency Use Authorization (EUA) for a SARS-CoV-2 assay outside of the U.S. Centers for Disease Control and Prevention. As of May 3rd, 2021, 289 total EUAs have been granted. Like influenza, there is no standard for defining limit of detection (LoD), but rather guidance that analytical sensitivity/LoD be established as the level that gives a 95% detection rate in at least 20 replicates. Here we compare the performance characteristics of SARS-CoV-2 tests receiving EUA by standardizing sensitivity to a common unit of measure and assess the variability in LoD between tests. Additionally, we looked at factors that may impact sensitivities due to lack of standardization of the test development process and compare results for a standardized reference panel for comparative analysis within a subset of EUA tests offered by the U.S. Food and Drug Administration.

AACC Guidance Document on the Use of Point-of-Care Testing in Fertility and Reproduction

Background

The AACC Academy revised the reproductive testing section of the Laboratory Medicine Practice Guidelines: Evidence-Based Practice for Point-of-Care Testing (POCT) published in 2007.

Methods

A panel of Academy members with expertise in POCT and laboratory medicine was formed to develop guidance for the use of POCT in reproductive health, specifically ovulation, pregnancy, premature rupture of membranes (PROM), and high-risk deliveries. The committee was supplemented with clinicians having Emergency Medicine and Obstetrics/Gynecology training.

Results

Key recommendations include the following. First, urine luteinizing hormone (LH) tests are accurate and reliable predictors of ovulation. Studies have shown that the use of ovulation predicting kits may improve the likelihood of conception among healthy fertile women seeking pregnancy. Urinary LH point-of-care testing demonstrates a comparable performance among other ovulation monitoring methods for timing intrauterine insemination and confirming sufficient ovulation induction before oocyte retrieval during in vitro fertilization. Second, pregnancy POCT should be considered in clinical situations where rapid diagnosis of pregnancy is needed for treatment decisions, and laboratory analysis cannot meet the required turnaround time. Third, PROM testing using commercial kits alone is not recommended without clinical signs of rupture of membranes, such as leakage of amniotic fluid from the cervical opening. Finally, fetal scalp lactate is used more than fetal scalp pH for fetal acidosis due to higher success rate and low volume of sample required.

Conclusions

This revision of the AACC Academy POCT guidelines provides recommendations for best practice use of POCT in fertility and reproduction.

Refining interpretation of transcutaneous bilirubin measurement in newborns born late preterm

BACKGROUND

Transcutaneous bilirubin (TCB) monitoring is widely used for jaundice screening in the newborn period. Limited data exists on adjusting TCB for bias in late preterm infants. The objective of this study was to determine the median bias between transcutaneous bilirubin and total serum bilirubin levels in newborns born at 35-36 weeks' gestation.

METHODS

This was a retrospective cohort study of late preterm infants born at 35-0/7 to 36-6/7 weeks' gestation who were admitted to a level III neonatal intensive care unit from May 2018 to February 2020. Transcutaneous and total serum bilirubin levels were assessed within 2 h of each other during the first 60 h of life. Bland-Altman plots were used to evaluate transcutaneous bilirubin bias. Bilirubin risk stratification based on age (in hours) was done using an adaptation of the Bhutani nomogram for transcutaneous, adjusted transcutaneous, and total serum bilirubin measurements.

RESULTS

The median bias between transcutaneous and total serum bilirubin bias was 2.4 mg/dL (IQR 1.7-3.4, 95% CI 2.2-2.7). The kappa statistic demonstrated slight agreement between the unadjusted transcutaneous bilirubin and total serum bilirubin (k = 0.033, p = 0.194. The kappa statistic demonstrated fair agreement between an adjusted transcutaneous bilirubin (subtract 1 mg/dL) and total serum bilirubin (k = 0.298, p < 0.0001) and moderate agreement between another adjusted transcutaneous bilirubin (subtract 2 mg/dL) and total serum bilirubin (k = 0.430, p < 0.0001).

CONCLUSION

In a single center study of late preterm infants, transcutaneous bilirubin systematically overestimated the total serum bilirubin level. Subtracting 1 mg/dL from the transcutaneous bilirubin identified infants with total serum bilirubin levels in the high or high intermediate risk range. Adjusting the transcutaneous bilirubin prior to risk stratification may reduce unnecessary blood draws for total serum bilirubin. Studies of racially and ethnically diverse newborns using various transcutaneous bilirubin meters are needed prior to broad application of the adjusted transcutaneous bilirubin approach.

Evaluation of the Visby medical COVID-19 point of care nucleic acid amplification test

Rapid and widespread diagnostic testing is critical to providing timely patient care and reducing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Recently, the Visby Medical COVID-19 point of care (POC) test was granted emergency use authorization (EUA) for qualitative detection of SARS-CoV-2 nucleic acid at the point of care. We evaluated its performance characteristics using residual specimens (n = 100) collected from Mayo Clinic patients using nasopharyngeal (NP) swabs and placed in viral transport media (VTM). The same specimen was tested using both the laboratory reference method (RT-qPCR) and Visby test. The reference methods utilized included a laboratory developed test with EUA (Mayo Clinic Laboratories, Rochester, MN) using the TaqMan assay on a Roche Light Cycler 480 or a commercially available EUA platform (cobas® SARS-CoV-2; Roche Diagnostics, Indianapolis, IN). Positive, negative, and overall percent agreement between the Visby COVID-19 test and the reference method were calculated. Additionally, the limit of detection (LoD) claimed by the manufacturer (1112 copies/mL) was verified with serial dilutions of heat inactivated virus. The Visby COVID-19 test correctly identified 29/30 positive samples and 69/70 negative samples, resulting in an overall concordance of 98.0%, positive percent agreement of 96.7%, and negative percent agreement of 98.6%. The abbreviated LoD experiment showed that the analytical sensitivity of the method is as low as or lower than 500 copies/mL. Our study demonstrated that Visby COVID-19 is well-suited to address rapid SARS-CoV-2 testing needs. It has high concordance with central laboratory-based RT-qPCR methods, a low rate of invalid results, and superior analytical sensitivity to some other EUA POC devices.

Analytical and Clinical Considerations in Implementing the Roche Elecsys Troponin T Gen 5 STAT Assay

OBJECTIVES

To evaluate the analytical and clinical performance characteristics of the fifth-generation troponin T reagent.

METHODS

Troponin T was measured in 2,332 paired serum and plasma samples from emergency department and hospital patients using the fourth- and fifth-generation reagents. Testing was repeated after recentrifugation to determine the frequency of analytical outliers and percentage of patients with elevated values for each assay. We conducted separate experiments to determine the effects of biotin and hemolysis interference, as well as measure interinstrument variability, for fifth-generation troponin T.

RESULTS

Analytic outliers occurred more frequently using the fifth-generation reagent (3.4%) compared with the fourth-generation reagent (1.0%). The frequency of elevated troponin T above the 99th percentile upper reference limit was 26% for the fourth-generation reagent and 52% for the fifth-generation reagent. Clinically significant assay interference by biotin was observed at 20 ng/mL, but hemolysis interference was not observed until an H index of 150. Instrument-to-instrument variability between e411 and e601/602 instrument platforms is predicted to confound clinical interpretation of troponin changes.

CONCLUSIONS

Analytical outliers and instrument-to-instrument variability are the two analytical variables most likely to confound interpretation of changes in fifth-generation troponin T results over time.

Professional Certification in Point-of-Care Testing

Professional certification is affirmation and documentation that the certified individual has the knowledge, training, and skills necessary to practice some aspect of medicine or other profession. Herein is a description of the genesis of a professional certification in point of care testing (POCT), inclusive of rationale and goals. A distinction between professional certification and certificate training programs is made. Details regarding eligibility to sit for the board exam are provided along with a list exam content areas. Finally, successes of this professional certification program are highlighted.

Evaluation of the genalyte maverick SARS-CoV-2 multi-antigen serology panel

Serologic testing for SARS-CoV-2 can be used for evaluation of past infection in individual patients and for community seroprevalence studies. We evaluated the analytical and clinical performance of the Genalyte Maverick SARS-CoV-2 Multi-Antigen Serology Panel compared to the Roche Elecsys Anti-SARS-CoV-2 nucleocapsid (NC) qualitative immunoassay, using well characterized clinical serum samples. A total of 143 pre-pandemic sera and 48 sera collected from patients with a negative molecular SARS-CoV-2 result were used for specificity studies. For sensitivity analyses, 179 sera were used, obtained 3-7 days, 8-14 days, or ≥ 15 days after symptom onset from patients with confirmed SARS-CoV-2 infection. Specificity was determined to be 95.3% (182/191) for the Genalyte Maverick. Overall sensitivity of the Genalyte Maverick was similar to that observed for the Roche Elecsys NC test, 79.3% (142/179) vs. 76.5% (137/179), respectively. Genalyte Maverick trended, without statistical significance, towards higher sensitivity as compared to the Roche Elecsys NC test in the 3-7 days (11/25 vs. 9/25, respectively) and 8-14 days (21/28 vs. 19/28, respectively) post-symptom onset sample sets, but was identical in the ≥ 15 days post-symptom onset group (106/116 vs. 106/116, respectively). Therefore, the Genalyte Maverick serologic test had similar overall sensitivity to the Roche Elecsys NC assay, but may have slightly improved sensitivity for early seroconversion. The lower Genalyte Maverick specificity as compared to the Roche Elecsys NC assay as reported by other studies (>99%), may necessitate confirmatory testing of positive Genalyte Maverick results if implemented for clinical use.

The Elevated High-Sensitivity Cardiac Troponin T Pilot: Diagnoses and Outcomes

OBJECTIVE

To identify the diagnoses and outcomes associated with elevated high sensitivity cardiac troponin T (hs-cTnT) compared with the 4th-generation troponin T and to validate the Mayo Clinic hs-cTnT myocardial infarction algorithm cutoff values.

PATIENTS AND METHODS

Consecutive blood samples of patients presenting to the emergency department between July 2017 and August 2017, who had 4th-generation troponin T, were also analyzed using the hs-cTnT assay. Troponin T values, discharge diagnoses, comorbidities, and outcomes were assessed. In addition, analyses of sex-specific and hs-cTnT cutoff values were assessed.

RESULTS

Of 830 patients, 32% had an elevated 4th-generation troponin T, whereas 64% had elevated hs-cTnT. With serial sampling, 4th-generation troponin missed a chronic myocardial injury pattern and acute myocardial injury pattern in 64% and 16% of patients identified with hs-cTnT, respectively. Many of these "missed" patients had discharge diagnoses associated with cardiovascular disease, infection, or were postoperative. Five of the 6 patients with unstable angina ruled in for myocardial infarction.

CONCLUSION

There were many increases in hs-cTnT that were missed by the 4th-generation cTnT assay. Most new increases are not related to acute cardiac causes. They were more consistent with chronic myocardial injury. High-sensitivity cTnT did reclassify most patients with unstable angina as having non-ST-elevation myocardial infarction. Older age, more comorbidities, and lower hemoglobin were associated with elevated hs-cTnT. Our data also support the use of our sex-specific cutoff values.

Analytical sensitivity and specificity of four point of care rapid antigen diagnostic tests for SARS-CoV-2 using real-time quantitative PCR, quantitative droplet digital PCR, and a mass spectrometric antigen assay as comparator methods

BACKGROUND

We evaluated the analytical sensitivity and specificity of four rapid antigen diagnostic tests (Ag RDTs) for SARS-CoV-2, using reverse transcription quantitative PCR (RT-qPCR) as the reference method; and further characterizing samples using droplet digital quantitative PCR (ddPCR) and a mass spectrometric antigen test.

METHODS

350 (150 negative and 200 RT-qPCR positive) residual phosphate buffered saline (PBS) samples were tested for antigen using the BD Veritor lateral flow (LF), ACON LF, ACON fluorescence immunoassay (FIA), and LumiraDx FIA. ddPCR was performed on RT-qPCR positive samples to quantitate the viral load in copies/mL applied to each Ag RDT. Mass spectrometric antigen testing was performed on PBS samples to obtain a set of RT-qPCR positive, antigen positive samples for further analysis.

RESULTS

All Ag RDTs had nearly 100% specificity compared to RT-qPCR. Overall analytical sensitivity varied from 66.5% to 88.3%. All methods detected antigen in samples with viral load >1,500,000 copies/mL RNA, and detected ≥75% of samples with viral load of 500,000 to 1,500,000 copies/mL. The BD Veritor LF detected only 25% of samples with viral load between 50,000-500,000 copies/mL, compared to 75% for the ACON LF device and >80% for LumiraDx and ACON FIA. The ACON FIA detected significantly more samples with viral load <50,000 copies/mL compared to the BD Veritor. Among samples with detectable antigen and viral load <50,000 copies/mL, sensitivity of the Ag RDT varied between 13.0% (BD Veritor) and 78.3% (ACON FIA).

CONCLUSIONS

Ag RDTs differ significantly in analytical sensitivity, particularly at viral load <500,000 copies/mL.

Unintended Consequence of High-Dose Vitamin C Therapy for an Oncology Patient: Evaluation of Ascorbic Acid Interference With Three Hospital-Use Glucose Meters

The use of high-dose vitamin C in cancer care has offered promising results for some patients. However, the intravenous (IV) doses used for these patients can reach concentrations that interfere with some strip-based glucose meters. We characterized the impact of vitamin C interference, from standard to the very high doses used for some cancer protocols, using three different hospital-use glucose meters. For two of the three devices tested, increasing concentrations of ascorbic acid caused false elevations in the glucose measurements. The third glucose meter did not provide inaccurate results, regardless of the vitamin C concentration present. Rather, above a certain threshold, the device generated error messages and no results could be obtained.

Is It Time to Remove Total Calcium from the Basic and Comprehensive Metabolic Panels? Assessing the Effects of American Medical Association-Approved Chemical Test Panels on Laboratory Utilization

BACKGROUND

The necessity of individual tests within the most commonly used disease-oriented test panels has not been well established. We evaluated test-ordering practices for total calcium, both before and after implementation of American Medical Association (AMA)-approved panels (basic metabolic panel [BMP] and comprehensive metabolic panel [CMP]) in our electronic ordering system.

METHODS

We performed a retrospective review of all total calcium orders placed during April and June 2018, before and after implementation of the panels. Orders from inpatient, outpatient, and emergency department (ED) care units were totaled, and the percentage of abnormal test results was calculated. We then queried institutional databases to determine the number of unique patients with calcium-related diagnoses and compared the rates from a 5-month period both before and after implementation of the panels.

RESULTS

Total test volumes and tests per unique patient increased by more than 3-fold after implementation of calcium-containing AMA-approved panels, with the majority of those orders coming from BMPs and CMPs. The rate of low calcium values increased because of the shift toward more inpatient testing; however, the percentage of abnormal results within each patient population (inpatient, outpatient, ED) decreased. The prevalence of hypo- and hypercalcemia-related diagnoses among patients in the 5 months after implementation did not change significantly (1.29% before implementation vs 1.27% after implementation).

CONCLUSIONS

Implementation of BMPs and CMPs dramatically increased total calcium testing volumes without changing the rate of calcium-related diagnoses. The results suggest that the increase in total calcium orders associated with panel-based testing largely constitutes excess or unnecessary testing.

Error simulation modeling to assess the effects of bias and precision on bilirubin measurements used to screen for neonatal hyperbilirubinemia

OBJECTIVES

Error simulation models have been used to understand the relationship between analytical performance and clinical outcomes. We developed an error simulation model to understand the effects of method bias and precision on misclassification rate for neonatal hyperbilirubinemia using an age-adjusted risk assessment tool.

METHODS

For each of 176 measured total bilirubin (TSB_M) values, 10,000 simulated total bilirubin (TB_S) values were generated at each combination of bias and precision conditions for coefficient of variation (CV) between 1 and 15%, and for biases between -51.3 μmol/L and 51.3 μmol/L (-3 and 3 mg/dL) fixed bias. TB_S values were analyzed to determine if they were in the same risk zone as the TSB_M value. We then calculated sensitivity and specificity for prediction of ≥75th percentile for postnatal age values as a function of assay bias and precision, and determined the rate of critical errors (≥95th percentile for age TSB_M with <75th percentile TB_S).

RESULTS

A sensitivity >95% for predicting ≥75th percentile bilirubin values was observed when there is a positive fixed bias of greater than 17.1 μmol/L (1.0 mg/dL) and CV is maintained ≤10%. A specificity >70% for predicting <75th percentile bilirubin values was observed when positive systematic bias was 17.1 μmol/L (1 mg/dL) or less at CV ≤ 10%. Critical errors did not occur with a frequency >0.2% until negative bias was -17.1 μmol/L (-1 mg/dL) or lower.

CONCLUSIONS

A positive systematic bias of 17.1 μmol/L (1 mg/dL) may be optimal for balancing sensitivity and specificity for predicting ≥75th percentile TSB values. Negative systematic bias should be avoided to allow detection of high risk infants and avoid critical classification errors.

Evaluation of the Cue Health point-of-care COVID-19 (SARS-CoV-2 nucleic acid amplification) test at a community drive through collection center

Point-of-care (POC) tests are in high demand in order to facilitate rapid care decisions for patients suspected of SARS-CoV-2. We conducted a clinical validation study of the Cue Health POC nucleic acid amplification test (NAAT) using the Cue lower nasal swab, compared to a reference NAAT using standard nasopharyngeal swab, in 292 symptomatic and asymptomatic outpatients for SARS-CoV-2 detection in a community drive through collection setting. Positive percent agreement between Cue COVID-19 and reference SARS-CoV-2 test was 91.7% (22 of 24); or 95.7% (22 of 23) when one patient with no tie-breaker method was excluded. Negative percent agreement was 98.4% (239 of 243), and there were 25 (8.6%) invalid or canceled results. The Cue COVID-19 test demonstrated very good positive and negative percent agreement with central laboratory tests and will be useful in settings where accurate POC testing is needed to facilitate management of patients suspected of COVID-19.

Platelet transfusion: The effects of a fluid warmer on platelet function

Platelet (PLT) transfusions are an important component of hemostatic resuscitation. The AABB has published several guidelines recommending that PLT units should not be infused through blood warming devices.

STUDY DESIGN AND METHODS

Thirty-one units of hospital blood bank apheresis PLTs were obtained. PLT-rich plasma (PRP) aggregometry and thromboelastography (TEG) were performed on the unit samples before and after the units were infused through a Ranger blood/fluid warming device.

RESULTS

There were no differences in any of the aggregometry results before and after infusion of the PLTs through the blood warmer (all P > .32). There was a significant reduction in the TEG maximum amplitude (MA) of 69.8 ± 7.9 mm before and 66.0 ± 8.8 mm after (P < .001) infusion of the PLTs through the blood warmer and α angle 61.8 ± 9.4° before and 59.3 ± 8.2° after (P = .044) infusion of the PLTs through the blood warmer, although both mean values were within normal range for the TEG and not clinically significant. There were very good correlations of aggregometry and TEG results before and after infusion of the PLTs through the blood warmer device.

CONCLUSION

This study did not demonstrate significant deleterious effect on PLT function from infusing apheresis PLT units through a blood warming device by PRP aggregometry. We did detect a statistically significant-but not clinically significant-reduction in TEG MA and α angle. The prohibition of transfusing PLT units though the Ranger blood warming device is not indicated.

Evaluation of automated synovial fluid total cell count and percent polymorphonuclear leukocytes on a Sysmex XN-1000 analyzer for identifying patients at risk of septic arthritis

BACKGROUND

Total cell counts (TC-BF) and percent polymorphonuclear cells (%PMN) of synovial fluid (SF) aspirates provide important cues for the timely diagnosis and management of septic arthritis. To facilitate faster turnaround time, we compared automated to manual TC-BF and differential counts in order to identify reporting cut-offs for automated TC-BF and %PMN that would allow release of automated results concordant with manual counts and differentials.

METHODS

Automated TC-BF and %PMN counts of a non-validated analyzer (Analyzer-B in STAT laboratory) were compared to a validated analyzer (Analyzer-A) and manual TC-BF counts and cytospin differentials. Concordance and %differences of Analyzer-B versus Analyzer-A and manual counts were assessed by linear regression analysis and Bland-Altman comparison.

RESULTS

Overall, automated and manual counts displayed good correlation. A majority of samples demonstrated unacceptable (>20%) differences between automated and manual counts at lower TC-BF (<10,000 cells/μl) and %PMN (<60%).

CONCLUSIONS

Based on good overall correlation and fewer samples with unacceptable (>20%) differences between automated and manual counts, we adopted TC-BF > 10,000 cells/μl and %PMN > 60% as cutoffs for reporting automated counts. These cutoffs minimize differences between automated and manual cell counts and differentials and would allow rapid automated reporting in the vast majority of septic arthritis cases.

Test Utilization Proposal for Reflex Bilirubin Testing: Why Order Two Tests When One Will Do?

BACKGROUND

Reflex testing algorithms are effective tools to reduce unnecessary laboratory testing. Direct (conjugated) bilirubin (DB) and total bilirubin (TB) are often ordered together at our institution. Therefore, the objective of our study was to evaluate the potential impact of performing reflex testing for DB when TB is elevated.

METHODS

We performed a retrospective review of test orders (patients ≥18 years of age) for DB, TB, or for both DB and TB on the same accession number received in our stat laboratory from January through April 2017. The orders were binned into 4 categories depending on the results from each individual test: (a) DB normal and TB normal, (b) DB normal and TB high, (c) DB high and TB normal, and (d) DB high and TB high. The percentage of orders and median (range) test result for each category was calculated.

RESULTS

During the months evaluated, a total of 4828 stat orders were placed for DB, TB, or both DB and TB. A total of 4296 stat orders (89%) were placed with both DB and TB on the same accession number for 4158 unique patients. Of those orders, the vast majority of tests (87.3%) contained normal results for both analytes; only 12.7% of orders contained ≥1 abnormal result.

CONCLUSIONS

The majority of all bilirubin tests ordered stat for emergency department and hospitalized patients have values within the reference interval. Consequently, if reflex testing were executed on elevated TB, a large number of DB tests could be avoided.

Estimating short- and long-term reference change values and index of individuality for tests of platelet function

BACKGROUND

In order to manage risks of bleeding and thrombosis after some surgical procedures, platelet function is often measured repeatedly over days or weeks using laboratory tests of platelet function. To interpret test results in the perioperative period, it is necessary to understand analytical, biological and between-person variation.

METHODS

We collected three separate blood specimens from 16 healthy volunteers on the first study day, and one additional specimen from each volunteer 1, 2, and 3 months later. Arachidonic acid-induced and adenosine diphosphate (ADP)-induced platelet function were measured in duplicate by whole blood impedance aggregometry using Multiplate (ASPI/ADP tests) and VerifyNow (Aspirin Reaction Units [ARU] and P2Y12 Reaction Units [PRU]). The analytical variation (CV_A), within-subject variation (CV_I), between-subject variation (CV_G), index of individuality (II), and reference change values (RCV) were calculated.

RESULTS

VerifyNow ARU demonstrated the smallest short-term and long-term variability (CV_A, CV_I, and CV_G ~1%), resulting in short- and long-term RCV values <5%. II was also higher (1.92) for VerifyNow ARU than other platelet function tests. Multiplate ASPI and ADP tests had the highest RCV both short-(19.0% and 25.2%, respectively) and long-term (32.1% and 39.6%, respectively) due to increased CV_A (>5%) and CV_I (3.9-13.1%). VerifyNow PRU had a lower RCV than Multiplate ADP; but was the only test with II <0.6.

CONCLUSIONS

VerifyNow ARU results can be interpreted relative to a fixed cut-off or population-based reference interval; or relative to small changes in an individual's previous values. VerifyNow PRU and Multiplate ASPI and ADP tests should only be interpreted based upon relative change; and can only distinguish relatively large (>23%) changes over several weeks.

Relationship between free hemoglobin (hemolysis), potassium and ionized calcium in lithium heparin blood gas samples collected intraoperatively

OBJECTIVE

Develop sample acceptability rules by determining the relationship between free hemoglobin level (hemolysis) and potassium or ionized calcium in blood gas samples collected intraoperatively.

DESIGN AND METHODS

Hemolysis was assessed visually or by H index for lithium heparin blood gas samples collected intraoperatively. During periods one and three this was done using two different rules for visual assessment of centrifuged lithium heparin plasma. During period two H index was measured for all visually hemolyzed samples on a Roche Cobas c501 analyzer to determine acceptability. Potassium and ionized calcium were measured in 75 lithium heparin whole blood samples on a Radiometer ABL90 to correlate H index and potassium or ionized calcium.

RESULTS

During period one 35 of 5808 (0.6%) blood gas samples had visual hemolysis levels exceeding tolerance for reporting of potassium. By switching to measured H index using a laboratory-established threshold, during period 2 we estimate that 171 of 5396 (3.2%) blood gas samples exceeded the H index threshold for reporting of potassium. In 75 intraoperative blood gas samples with H index and whole blood potassium and ionized calcium measured; we observed no relationship between H index and potassium or ionized calcium. During period 3 we switched to visual assessment of hemolysis with a greater tolerance for hemolysis; with only 3 of 5345 (0.06%) samples exceeding the new visual hemolysis threshold.

CONCLUSION

For blood gas samples collected intraoperatively, there is no relationship between hemolysis and measured potassium or ionized calcium. The results suggest that only grossly hemolyzed intraoperative blood gas samples should be rejected for measurement of whole blood potassium and ionized calcium.

High-Sensitivity Troponin in Patients With Coronary Artery Endothelial Dysfunction

BACKGROUND

Coronary endothelial dysfunction (CED) is associated with recurrent ischemia. The role of high-sensitivity cardiac troponin I (hscTnI) levels in patients with CED has not been established.

METHODS

Patients with suspected ischemia, who underwent clinically indicated coronary angiography and were found to have non-obstructive coronary artery disease, were included in the study. CED was defined as ≤50% increase in coronary blood flow from baseline and/or a decrease in epicardial coronary artery diameter >20% in response to maximal dosages of acetylcholine. HscTnI was measured at the time of the procedure using the Architect hscTnI assay (Abbott).

RESULTS

Of 299 patients, 60 had normal endothelial function and 239 patients had abnormal endothelial function. The median age of the population was 52 years (interquartile range [IQR], 45-60 years). Patients with abnormal endothelial function had significantly higher log hscTnI values when compared to patients with normal endothelial function (0.9 ng/L [IQR, 0.7-1.4 ng/L] vs 0.7 ng/L [IQR, 0.7-1.1 ng/L]; P=.04). An hscTnI value >12.5 ng/L was 100% specific for the presence of endothelial dysfunction (100% positive predictive value). There were 39 major adverse cardiovascular events during follow-up. In patients with normal endothelial function, hscTnI levels were significantly higher in patients who developed major adverse cardiac events when compared to patients who did not (1.35 ng/L [IQR, 1.1-2.1 ng/L] vs 0.7 ng/L [IQR, 0.7-1.1 ng/L]; P=.02).

CONCLUSION

Our findings suggest that endothelial dysfunction may be associated with higher baseline hscTnI levels, suggesting increased myocardial injury in this population of patients. Additional studies are necessary to further define the role of hscTnI in risk stratification in this population.

Blood gas sample spiking with total parenteral nutrition, lipid emulsion, and concentrated dextrose solutions as a model for predicting sample contamination based on glucose result

OBJECTIVE

Evaluate the effects of blood gas sample contamination with total parenteral nutrition (TPN)/lipid emulsion and dextrose 50% (D50) solutions on blood gas and electrolyte measurement; and determine whether glucose concentration can predict blood gas sample contamination with TPN/lipid emulsion or D50.

DESIGN AND METHODS

Residual lithium heparin arterial blood gas samples were spiked with TPN/lipid emulsion (0 to 15%) and D50 solutions (0 to 2.5%). Blood gas (pH, pCO2, pO2), electrolytes (Na+, K+ ionized calcium) and hemoglobin were measured with a Radiometer ABL90. Glucose concentration was measured in separated plasma by Roche Cobas c501. Chart review of neonatal blood gas results with glucose >300 mg/dL (>16.65 mmol/L) over a seven month period was performed to determine whether repeat (within 4 h) blood gas results suggested pre-analytical errors in blood gas results. Results were used to determine whether a glucose threshold could predict contamination resulting in blood gas and electrolyte results with greater than laboratory-defined allowable error.

RESULTS

Samples spiked with 5% or more TPN/lipid emulsion solution or 1% D50 showed glucose concentration >500 mg/dL (>27.75 mmol/L) and produced blood gas (pH, pO₂, pCO₂) results with greater than laboratory-defined allowable error. TPN/lipid emulsion, but not D50, produced greater than allowable error in electrolyte (Na⁺,K⁺,Ca⁺⁺,Hb) results at these concentrations. Based on chart review of 144 neonatal blood gas results with glucose >250 mg/dL received over seven months, four of ten neonatal intensive care unit (NICU) patients with glucose results >500 mg/dL and repeat blood gas results within 4 h had results highly suggestive of pre-analytical error. Only 3 of 36 NICU patients with glucose results 300-500 mg/dL and repeat blood gas results within 4 h had clear pre-analytical errors in blood gas results.

CONCLUSION

Glucose concentration can be used as an indicator of significant blood sample contamination with either TPN/lipid emulsion or D50 solution. NICU blood gas samples with glucose ≥300 mg/dL should be considered potentially contaminated, and samples with glucose >500 mg/dL have a risk for contamination.

Defining the limitations of transcutaneous bilirubin measurement in late preterm newborns

OBJECTIVE

The objective of this study is to determine the impact of postnatal age on the bias between transcutaneous (TcB) and total serum bilirubin (TSB), and evaluate a TcB screening protocol.

STUDY DESIGN

Preterm and term infants had paired TcB and TSB performed on days 1 to 3 of life; a subset of preterm infants had measurements on days 4 to 7. Sensitivity and specificity of TcB (plotted on an age-specific TSB nomogram) for prediction of high-intermediate (HIR) or high-risk TSB were calculated.

RESULTS

Median TcB bias was 2.6 and 2.5 mg dl^-1 for term and preterm infants in the first 3 days of life, respectively. However, median bias was 2.2 mg dl^-1 for preterm infants at 4 to 7 days of life. TcB in preterm infants predicted HIR or high-risk TSB with 94% sensitivity and 56% specificity.

CONCLUSION

TcB screening protocols developed for term infants can be used for late preterm infants in the first 3 days of life.

Neonatal Intensive Care Unit Quality Initiative: Identifying Preanalytical Variables Contributing to Specimen Hemolysis and Measuring the Impact of Evidence-Based Practice Interventions

OBJECTIVES

Blood specimen hemolysis is a major cause of sample recollection in the neonatal intensive care unit. We aimed to reduce the hemolysis rate from 6.3% at baseline to less than 4% within the 9 months' duration of the study.

METHODS

Intravenous infusion of lipid emulsion during sample collection, sample collection site, and blood sample transportation methods were investigated as possible contributors to hemolysis. Subsequently, two practice improvements were implemented: pausing lipid emulsion infusion prior to collection and slowing withdrawal rates through arterial catheters.

RESULTS

Samples were more likely to be hemolyzed if they were collected during lipid infusion and subsequently transported by pneumatic tube or collected through an arterial catheter. Retrospective analysis demonstrated a decreased number of tests cancelled due to specimen hemolysis (3.5%) after our interventions.

CONCLUSIONS

We identified three variables contributing to hemolysis and instituted two clinical practice interventions to significantly reduce test cancellations due to hemolysis.

Implementation of Clinical Decision Support Rules to Reduce Repeat Measurement of Serum Ionized Calcium, Serum Magnesium, and N-Terminal Pro-B-Type Natriuretic Peptide in Intensive Care Unit Inpatients

BACKGROUND

We assessed the impact of clinical decision support (CDS) rules within the electronic health record for ionized calcium (iCa), serum magnesium (Mg), and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in intensive care unit (ICU) inpatients at a large academic center.

METHODS

A repeat order for measurement of iCa or Mg placed within 24 (iCa) or 48 (Mg) h of a previously nonactionable result, or additional orders for NT-proBNP beyond 1 within a single hospitalization, triggered a CDS pop-up alert showing the prior result and offering the opportunity to cancel the order or to place the order after entering an indication for repeat testing. The number of tests performed for each of these analytes and incidence of adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia were compared between the 90-day period before CDS implementation and two 90-day periods immediately following.

RESULTS

iCa test volumes decreased by 48%, Mg by 39%, and NT-proBNP by 28% in the 90-day period immediately following implementation and remained decreased by 54%, 49%, and 22%, respectively, during the following 90-day period (all P values <0.0002). Adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia did not increase (all P-values >0.17).

CONCLUSIONS

Implementation of CDS dramatically decreased repeat testing of iCa, Mg, and NT-proBNP without adversely impacting clinical outcomes in the ICU. Expansion of the rules from the ICU units to include the entire hospitalized patient population and expansion to additional analytes is expected to lead to further reductions in testing.

Relation of Activated Clotting Times During Percutaneous Coronary Intervention to Outcomes

Monitoring anticoagulation using the activated clotting time (ACT) in patients treated with heparin and undergoing percutaneous coronary intervention (PCI) is one of the most frequently used tests in invasive cardiology. However, despite its widespread use and guideline endorsement, uncertainty remains regarding the association of ACT with outcomes in contemporary practice. We reviewed all PCI procedures performed at the Mayo Clinic (Rochester, Minnesota) from October 2001 to December 2012 and evaluated the association between the ACT before device activation and in-hospital and 1-year outcomes. ACT values were grouped into tertiles for descriptive purposes and analyzed as a continuous variable for assessment of outcomes. We used logistic and Cox proportional hazards regression models to estimate the association of ACT and outcomes. Of the 12,055 patients who underwent PCI with an ACT value before device activation, 3,977 (33.0%) had an ACT <227, 4,046 (33.6%) had an ACT 227 to 285, and 4,032 (33.4%) had an ACT >285. Baseline and procedural characteristics were similar across ACT tertiles. In unadjusted analysis, higher ACT values were associated with death (p <0.001), bleeding (p = 0.024), procedural complication (p <0.001), and higher 1-year events (cardiac death, p <0.001; cardiac death/myocardial infarction, p = 0.022). After multivariable adjustment for baseline and procedural characteristics, ACT was not independently associated with in-hospital or 1-year ischemic, thrombotic, or bleeding outcomes. In conclusion, ACT values before device activation are not independently associated with clinically important outcomes in contemporary PCI practice.

Impact of Glucose Meter Error on Glycemic Variability and Time in Target Range During Glycemic Control After Cardiovascular Surgery

BACKGROUND

We retrospectively studied the impact of glucose meter error on the efficacy of glycemic control after cardiovascular surgery.

METHOD

Adult patients undergoing intravenous insulin glycemic control therapy after cardiovascular surgery, with 12-24 consecutive glucose meter measurements used to make insulin dosing decisions, had glucose values analyzed to determine glycemic variability by both standard deviation (SD) and continuous overall net glycemic action (CONGA), and percentage glucose values in target glucose range (110-150 mg/dL). Information was recorded for 70 patients during each of 2 periods, with different glucose meters used to measure glucose and dose insulin during each period but no other changes to the glycemic control protocol. Accuracy and precision of each meter were also compared using whole blood specimens from ICU patients.

RESULTS

Glucose meter 1 (GM1) had median bias of 11 mg/dL compared to a laboratory reference method, while glucose meter 2 (GM2) had a median bias of 1 mg/dL. GM1 and GM2 differed little in precision (CV = 2.0% and 2.7%, respectively). Compared to the period when GM1 was used to make insulin dosing decisions, patients whose insulin dose was managed by GM2 demonstrated reduced glycemic variability as measured by both SD (13.7 vs 21.6 mg/dL, P < .0001) and CONGA (13.5 vs 19.4 mg/dL, P < .0001) and increased percentage glucose values in target range (74.5 vs 66.7%, P = .002).

CONCLUSIONS

Decreasing glucose meter error (bias) was associated with decreased glycemic variability and increased percentage of values in target glucose range for patients placed on intravenous insulin therapy following cardiovascular surgery.

Agreement between whole blood and plasma sodium measurements in profound hyponatremia

OBJECTIVES

We compared two different methods of whole blood sodium measurement to plasma sodium measurement using samples in the profoundly hyponatremic range (Na < 120 mmol/L).

DESIGN AND METHODS

Whole blood pools with a range of low sodium values were generated using combinations and dilutions of pooled electrolyte-balanced lithium heparin samples submitted for arterial blood gas analysis. Each pool was analyzed five times on a Radiometer 827 blood gas analyzer and iSTAT analyzer. Pools were centrifuged to produce plasma, which was analyzed five times on a Roche Cobas c501 chemistry analyzer. An additional 40 fresh (analyzed on day of collection) excess lithium heparin arterial blood gas samples from 36 patients were analyzed on the Radiometer 827, iSTAT, and Cobas c501 as described above. The setting was a tertiary referral center. Blood samples were collected from a combination of patients in the intensive care unit, operating theaters and emergency room.

RESULTS

All methods demonstrated excellent precision, even in the profoundly hyponatremic measurement range (Na < 120 mmol/L using a plasma reference method). However, agreement between the methods varied with the degree of hyponatremia. In the profoundly hyponatremic range, Radiometer whole blood sodium values were nearly identical to plasma reference sodium, while iSTAT whole blood sodium showed a consistent positive bias relative to plasma sodium in this range.

CONCLUSION

If whole blood direct sodium measurements are compared with plasma sodium in profoundly hyponatremic patients consideration should be given to the use of Radiometer blood gas analyzers over iSTAT since the latter shows a positive bias relative to a plasma comparative method.

Precision and Reliability of 5 Platelet Function Tests in Healthy Volunteers and Donors on Daily Antiplatelet Agent Therapy

BACKGROUND

Anticoagulation protocols used during mechanical circulatory support call for titration of antiplatelet agents. We compared the precision and reliability of 5 platelet function tests in healthy volunteers and donors on daily antiplatelet therapy to distinguish their efficacy for titrating antiplatelet therapy.

METHODS

We assessed arachidonic acid–induced platelet function by light transmission aggregometry (LTA), Multiplate impedance aggregometry, VerifyNow, and platelet mapping by thromboelastography (TEG PM). We assessed ADP-induced platelet function by the same methods and flow cytometry. Forty healthy volunteers and 10–13 volunteers on daily aspirin and/or clopidogrel therapy were evaluated. We compared tests for intraassay precision, interassay precision (samples from 2 separate blood draws), and reliability coefficient.

RESULTS

For arachidonic acid–induced platelet aggregation in healthy volunteers, intra- and interassay CVs were ≤10% for all methods. Intra- and interassay precision among donors on daily aspirin was ≤30% for all methods except LTA (38% interassay CV) and TEG PM (95% intraassay and 104% interassay CV). For ADP-induced platelet function, intra- and interassay precision was ≤10% and ≤30% for all methods. Only Multiplate demonstrated moderate or greater (R &gt; 0.40) reliability coefficients for arachidonic acid–induced platelet function among all subjects. All methods of ADP-induced platelet function, except TEG PM, demonstrated substantial or greater (R &gt; 0.60) reliability among all subjects.

CONCLUSIONS

TEG PM is least suited to monitor effects of antiplatelet agents. Multiplate impedance aggregometry was the only method to demonstrate an acceptable reliability coefficient among healthy volunteers and donors on both aspirin and clopidogrel therapy.

Retrospective evaluation of the accuracy of Roche AccuChek Inform and Nova StatStrip glucose meters when used on critically ill patients

BACKGROUND

More stringent accuracy guidelines for hospital-use glucose meters have recently been published, but it remains unclear whether glucose meters can meet these accuracy guidelines when measurement is performed on critically ill patients with fresh whole blood samples.

MATERIALS AND METHODS

We performed a retrospective evaluation of a conventional (Roche Diagnostics [Indianapolis, IN] AccuChek® Inform) and a newer-generation (Nova Biomedical [Waltham, MA] StatStrip®) glucose system by comparing paired (drawn within 5 min of each other) whole blood glucose meter and laboratory serum glucose values obtained from intensive care unit (ICU) patients. We also performed a prospective evaluation of the accuracy of the Nova StatStrip.

RESULTS

The median (interquartile range) bias between Roche AccuChek Inform and serum laboratory glucose measurements was 11 (6-18) mg/dL, compared with a median bias between the Nova StatStrip and serum glucose measurements of 1 (-5 to 5) mg/dL. StatStrip met International Organization for Standardization 15197 and Clinical and Laboratory Standards Institute (CLSI) POCT12-A3 accuracy guidelines using both retrospective and prospective datasets.

CONCLUSIONS

The newer-generation (StatStrip) glucose meter met more stringent CLSI POCT12-A3 accuracy criteria because of reduced bias compared with the previous-generation device. Reduced glucose meter bias led to fewer insulin dosing discrepancies when the insulin dose determined from serum glucose was compared with that determined from the glucose meter value using the institutional glycemic control protocol.

Development and initial validation of a project-based rubric to assess the systems-based practice competency of residents in the clinical chemistry rotation of a pathology residency

CONTEXT

Systems-based practice (SBP) is 1 of 6 core competencies required in all resident training programs accredited by the Accreditation Council for Graduate Medical Education. Reliable methods of assessing resident competency in SBP have not been described in the medical literature.

OBJECTIVE

To develop and validate an analytic grading rubric to assess pathology residents' analyses of SBP problems in clinical chemistry.

DESIGN

Residents were assigned an SBP project based upon unmet clinical needs in the clinical chemistry laboratories. Using an iterative method, we created an analytic grading rubric based on critical thinking principles. Four faculty raters used the SBP project evaluation rubric to independently grade 11 residents' projects during their clinical chemistry rotations. Interrater reliability and Cronbach α were calculated to determine the reliability and validity of the rubric. Project mean scores and range were also assessed to determine whether the rubric differentiated resident critical thinking skills related to the SBP projects.

RESULTS

Overall project scores ranged from 6.56 to 16.50 out of a possible 20 points. Cronbach α ranged from 0.91 to 0.96, indicating that the 4 rubric categories were internally consistent without significant overlap. Intraclass correlation coefficients ranged from 0.63 to 0.81, indicating moderate to strong interrater reliability.

CONCLUSIONS

We report development and statistical analysis of a novel SBP project evaluation rubric. The results indicate the rubric can be used to reliably assess pathology residents' critical thinking skills in SBP.

Empiric validation of simulation models for estimating glucose meter performance criteria for moderate levels of glycemic control

BACKGROUND

We used simulation modeling to relate glucose meter performance criteria to insulin dosing errors for patients on a moderate glycemic control protocol (glucose target, 110-150 mg/dL) and empirically validated assumptions from simulation models using observed glucose meter and laboratory glucose values obtained nearly simultaneously.

SUBJECTS AND METHODS

The 25,948 glucose values from 1,513 patients on a moderate glycemic control protocol were used to represent the expected distribution of glucose values in this patient population. Simulation models were used to relate glucose meter analytical performance to insulin dosing errors assuming 10%, 15%, or 20% total allowable error (TEa). In addition, 4,017 paired glucose meter and serum laboratory glucose measurements drawn within 5 min of each other were used to generate an empiric dataset to validate simulation model assumptions relating glucose meter performance to insulin dosing errors.

RESULTS

Large (three or more category) insulin dosing errors are predicted to occur only under the 20% TEa condition. Two category insulin dosing errors were common (6-20% of all insulin dosing decisions) when 20% TEa was assumed, but frequency decreased to only 0.2% of dosing decisions when 10% TEa was modeled. When insulin dosing error rates were measured empirically by comparing paired glucose meter and laboratory glucose values, insulin dosing error rates were very similar to those predicted for the 20% TEa condition.

CONCLUSIONS

Both simulation models and empiric data demonstrate that glucose meters that perform at ≥20% TEa allow large insulin dosing errors during a moderate glycemic control protocol.

Fresh and citrated whole-blood specimens can produce different thromboelastography results in patients on extracorporeal membrane oxygenation

OBJECTIVES

To compare thromboelastography (TEG) tracings obtained from fresh and citrated whole-blood samples in patients on extracorporeal membrane oxygenation (ECMO) or after cardiopulmonary bypass and in healthy volunteers.

METHODS

Samples of fresh and citrated whole blood were analyzed for 25 patients and 4 healthy volunteers. Thromboelastography analysis was performed in both plain and heparinase cups.

RESULTS

In 5 of 6 patients on ECMO, use of citrated samples resulted in apparent partial or complete heparin reversal. In TEG tracings from patients following cardiopulmonary bypass, there was a slight hypercoagulable appearance in the citrated sample. No differences were noted between fresh and citrated samples from healthy volunteers whose blood was spiked with heparin.

CONCLUSIONS

In some patients on ECMO, use of samples collected in sodium citrate tubes for TEG analysis results in significant artifacts, which could lead to heparin overdosing in these patients.

Analytical performance of three point of care methods for pleural fluid pH analysis

OBJECTIVE

The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer.

DESIGN AND METHODS

An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range.

RESULTS

All methods demonstrated inter-assay CVs<0.1% at pH values of 7.1 and 7.6, and intra-assay CVs<0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH>7.6. For samples with pH<7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods.

CONCLUSIONS

Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.

Temporal sequence of major biochemical events during blood bank storage of packed red blood cells

BACKGROUND

We used sensitive spectroscopic techniques to measure changes in Band 3 oligomeric state during storage of packed red blood cells (RBC); these changes were compared to metabolic changes, RBC morphology, cholesterol and membrane protein loss, phospholipid reorganisation of the RBC membrane, and peroxidation of membrane lipid. The aim of the study was to temporally sequence major biochemical events occurring during cold storage, in order to determine which changes may underlie the structural defects in stored RBC.

MATERIALS AND METHODS

Fifteen RBC units were collected from normal volunteers and stored under standard blood bank conditions; both metabolic changes and lipid parameters were measured by multiple novel assays including a new mass spectrometric measurement of isoprostane (lipid peroxidation) and flow cytometric assessment of CD47 expression. Band 3 oligomeric state was assessed by time-resolved phosphorescence anisotropy, and RBC morphology by microscopy of glutaraldehyde-fixed RBC.

RESULTS

Extracellular pH decreased and extracellular potassium increased rapidly during cold storage. Band 3 on the RBC membrane aggregated into large oligomers early in the storage period and coincident with changes in RBC morphology. Membrane lipid changes, including loss of unesterified cholesterol, lipid peroxidation and expression of CD47, also changed early during the storage period. In contrast loss of acetylcholinesterase activity and haemolysis of RBC occurred late during storage.

DISCUSSION

Our results demonstrate that changes in the macromolecular organisation of membrane proteins on the RBC occur early in storage and suggest that lipid peroxidation and/or oxidative damage to the membrane are responsible for irreversible morphological changes and loss of function during red cell storage.

BD rapid serum tubes reduce false positive plasma troponin T results on the Roche Cobas e411 analyzer

OBJECTIVES

In an attempt to reduce false positive results and improve turnaround time, we investigated the BD Rapid Serum Tube as an alternate sample type to lithium heparin plasma for Roche Troponin T analysis on the Roche Cobas e411 analyzer.

DESIGN AND METHODS

BD Plasma Separator Tubes (PST) and Rapid Serum Tubes (RST) were collected in tandem from Emergency Department patients who had clinical orders for Troponin T over a 1 month period.

RESULTS

RST and PST samples yielded analytically and clinically concordant Troponin T results on the Roche Cobas e411. Rare false positive results in lithium heparin samples were not observed with rapid clot serum tubes.

CONCLUSIONS

RST samples are appropriate for stat Troponin T analysis, and appear to reduce the incidence of rare false positive Troponin T results obtained with lithium heparin samples.

Accuracy of neonatal transcutaneous bilirubin measurement in the outpatient setting

OBJECTIVE. To evaluate the effectiveness of transcutaneous bilirubin (TcB) measurement in predicting risk for neonatal hyperbilirubinemia in outpatients. DESIGN. Subjects were infants ≤8 days old seen in an outpatient clinic. Infants discharged with high-risk (HR) or high-intermediate risk (HIR) total serum bilirubin (TSB) values and jaundiced infants were recruited. TSB and TcB (BiliChek) levels were plotted on an hour-specific nomogram to determine risk for hyperbilirubinemia. RESULTS. A total of 79 infants provided 87 sets of TcB and TsB values. Mean bias and standard deviation between TcB and TsB was 1.5 ± 2.1 mg/dL for outpatients, compared with 2.7 ± 1.3 mg/dL for inpatients. The sensitivity and specificity of HR or HIR TcB for predicting an HR or HIR TSB were 87% and 58%, respectively. Of 9 infants readmitted for phototherapy, 1 had a low-risk TcB and high-risk TSB. CONCLUSIONS. TcB screening in the outpatient environment may not be safe and efficient.