Lack of observed interference by therapeutic monoclonal antibodies in select commonly utilized immunoassays

BACKGROUND

Therapeutic monoclonal antibodies (tmabs) have been hypothesized to interfere with immunoassay measurements, although studies investigating this potential new class of interference are lacking. This study evaluated the effects of tmabs used in cancers ipilimumab (Bristol Myers Squibb), nivolumab (Bristol Myers Squibb), pembrolizumab (Merck) and autoimmune disorders adalimumab (AbbVie), infliximab (Janssen) and vedolizumab (Takeda) in common immunoassays used in the clinical laboratory.

METHODS

Residual sera from 10 randomly chosen patients were split into two tubes and spiked with same volume (approximately 5 % final volume) of either saline (control) or 6 tmabs (final concentration of 100 μg/mL each). Concentrations from sixteen analytes in 19 different assays were assessed: TSH (Roche and Beckman), free thyroxine (Roche and Siemens), cortisol (Beckman), Cancer Antigens (CA): CA19-9 (Beckman), CA15-3 (Roche), CA125 (Roche), and CA27.29 (Siemens), carcinoembryonic antigen (Beckman), alpha-fetoprotein (Beckman), thyroglobulin (Beckman) and thyroglobulin antibodies (Beckman), thyroid peroxidase antibody (Beckman), beta-human chorionic gonadotropin (Roche and Beckman), total prostate-specific antigen (Roche), parathyroid hormone (Roche) and antinuclear antibodies IgG (Werfen). The tmab spiked residual sera were compared with matched saline spiked sera and percent error was assessed against allowable total error defined from biological variation or CLIA limits.

RESULTS

None of the tested immunoassays were affected by the presence of the tmabs, in samples within or outside assay reference intervals. The median % error among all immunoassays ranged between -2.0% (for TSH) to 2.7% (for TPO Ab assay).

CONCLUSION

These findings demonstrate no detectable tmab interference for the assessed immunoassays using spiked preparations of the tmabs in residual human sera. The findings are limited to the tmabs and immunoassays studied here.

Keep calm and invert on: Reducing blood recollection rates in the neonatal intensive care unit (NICU)

Background

Minimizing blood specimen recollection due to specimen integrity issues is a continuous quality improvement goal in the neonatal intensive care unit (NICU). Specimen integrity issues, such as clotting or hemolysis, are often the result of improper specimen collection processes and lead to blood loss requiring transfusion, additional painful procedures, and delays in patient care. Data collected from Mayo Clinic Hospital - Methodist Campus NICU at Mayo Clinic in Rochester, MN between January – July 2019 showed that clotted complete blood count (CBC) specimens accounted for one-third of rejected neonatal specimens followed by hemolyzed specimens for direct bilirubin (DBIL) testing. The aim of this project was to reduce the percent of CBC and DBIL tests canceled/specimens rejected due to specimen integrity issues in the NICU from 17% to 10% using the Plan-Do-Study-Act methodology.

Methods

A multidisciplinary quality improvement (QI) team was formed, inclusive of both NICU and laboratory representatives. Bedside direct observations (n=28) were performed by NICU nurses to help identify inconsistencies in the blood collection processes. A total of three Plan-Do-Study-Act (PDSA) cycles were conducted during the 2020-2021 time period. An assessment card was created and revised with each PDSA cycle. The card was completed by the nurse(s) present during the blood collection and initially identified the lab tests ordered, collection tubes, collection type (venipuncture, venous, capillary), number of tube inversions required, staff present during collection, any delays during collection, and whether the draw was deemed successful. Additionally, staff education videos for nursing and laboratory phlebotomy staff were created to demonstrate correct collection tube inversion technique.

Results

Direct observation identified inconsistent practices in tube inversion during specimen collection. The first PDSA cycle (n=207 collections, April 1 – July 13, 2021) introduced a verbal inversion count and utilization of the assessment card. The following cycle (n=336 collections, July 14 – October 10, 2021) implemented an educational video and modified the assessment card to include start and end time of the draw. The third cycle (n=243 collections, October 11 – November 30, 2021) used a simplified assessment card including patient label, tests ordered, tube type and inversions. The combined rejection rates for CBC and DBIL tests were 4.3%, 3.8% and 2.8% for the 1st, 2nd and 3rd PDSA cycles, respectively.

Conclusions

Our QI initiative reduced the specimen rejection rate for clotted CBC and hemolyzed DBIL specimens from 17% to 2.8% in the NICU. Interventions focused on improving tube inversion techniques and promoting collaborative relationships between phlebotomists and nursing staff. The use of educational videos and completion of assessment cards during collections were effective at reducing specimen rejection rates.

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.

Effect of pH on the Quantification of Common Chemistry Analytes in Body Fluid Specimens Using the Roche cobas Analyzer for Clinical Diagnostic Testing

OBJECTIVES

To determine the influence of pH on recovery of analytes in body fluids (BFs), investigate the mechanism of pH interference, measure the frequency of abnormal-pH BFs received, and compare pH measured by meter and paper.

METHODS

We performed pH titration in residual BFs. A low-pH BF was spiked and neutralized to investigate pH interference. We measured analytes on a Roche cobas c501 analyzer (Roche Diagnostics) and calculated the percent recovery. Measurement of pH using a meter and paper was conducted on 122 BF samples received in the laboratory.

RESULTS

Enzyme activity in BFs was unaffected when pH = 7.4-8.5 lactate dehydrogenase, pH = 7.3-10.2 amylase, pH = 6.0-9.9 lipase, and pH = 1.3-11.7 all other analytes. BFs had mean (range) pH of 8.0 (5.1-8.9), with a mean (range) difference (paper ‒ meter) of ‒0.4 (‒0.6 to 1.1).

CONCLUSIONS

Irreversible loss of enzyme activity occurs in BFs at low pH. Few clinical BFs have pH < 7.0, but laboratories should incorporate pH measurement in BF workflows.

Unexpected Vancomycin Pharmacokinetic Profile Secondary to Macromolecular Complexing: A Case Series

BACKGROUND

The optimal dosing and monitoring of vancomycin has been largely debated for decades, with key guideline changes for recommended monitoring in 2009 and 2020. Current and past practices for pharmacokinetic dose optimization use serum drug assays to guide dose adjustment to effectively balance efficacy and the risks of toxicity. These assays detect both bound and unbound serum concentrations. Vancomycin is believed to be 50%-55% protein bound in most cases; however, some variability in this parameter has been previously published. The authors report 2 cases of abnormal vancomycin pharmacokinetics discovered based on unexpected serum levels during routine clinical care.

METHODS

Unexpected vancomycin levels, observed during clinical care for 2 separate patients, were further evaluated to determine the source of the abnormal pharmacokinetics. In case 1, serial dilution was performed to assure that assay interference was not associated with the significant elevation (>100 mg/L). In both cases, samples were filtered using a Millipore Centrifree 30 KDa centrifugal filter to separate bound vancomycin, with a Protein G spin kit used to bind IgG and remove IgG complexes from the patient sample. In case 2, a polyethylene glycol precipitation was also performed to precipitate large-molecular-weight complexes.

RESULTS

In both cases, laboratory analysis revealed abnormal vancomycin protein-binding profiles with macromolecular complex formation. Immunoglobulin G played a role in the macrocomplex in both patients.

CONCLUSIONS

In cases of unusual or unexpected vancomycin pharmacokinetics in the absence of renal dysfunction, an abnormal protein-binding profile should be considered. Bound vancomycin may yield elevated serum levels, leading to poorly informed dose adjustments and risk for treatment failure. Given implications for therapeutic drug monitoring and unknown impacts on efficacy and toxicity, further investigations into population incidence and risk factors for abnormal protein binding of vancomycin are warranted.

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.

Challenges with At-home and Mail-in Direct-to-Consumer Testing: Preanalytical Error, Reporting Results, and Result Interpretation

Companies that offer direct-to-consumer (DTC) testing on specimens such as saliva, blood, or urine, allow consumers to order laboratory tests without the involvement of a health care provider. This approach allows individuals to have direct access to their own laboratory results, interpret them, and make decisions regarding their health care. However, as with conventional clinical laboratory testing, there are factors that will impact the accuracy of DTC test results and limitations that consumers need to be aware of. This article focuses on challenges with DTC testing specifically related to preanalytical errors, result reporting, and result interpretation.

Validation of a Commercial Reagent for the Depletion of Biotin from Serum/Plasma: A Rapid and Simple Tool to Detect Biotin Interference with Immunoassay Testing

BACKGROUND

It is important for clinical laboratories to have protocols for investigating suspected biotin interference in patient samples. VeraPrep Biotin™ is a commercial product used to rapidly deplete biotin from serum/plasma samples. The objectives of this study were to verify that VeraPrep Biotin™: (a) does not impact immunoassay analyte recovery in control samples and (b) can effectively deplete biotin from samples (both biotin-spiked and samples from donors who ingested biotin supplements).

METHODS

De-identified residual waste serum/plasma samples were combined to create 9 pools for each immunoassay. Plasma/serum samples (n = 23) were obtained from 6 healthy donors at varying times following ingestion of biotin (20 mg, 100 mg, or 200 mg). Nine Elecsys immunoassays were evaluated using the e 602 (Roche Diagnostics Inc.). Control, biotin-spiked (n = 10, ∼400 ng/mL), and donor samples were assayed pre- and post-VeraPrep treatment. Percentage analyte recovery [(posttreatment/pretreatment) × 100] was calculated for control samples. A laboratory-developed LC-MS/MS method was used to quantify biotin.

RESULTS

In control samples (n = 81), 90-110% analyte recovery was observed post-VeraPrep treatment in over 95% of samples (77/81). The pre- and post-VeraPrep treatment biotin concentration [mean ± standard deviation (SD)] for specimens spiked with up to 500 ng/mL biotin was 357 ± 47 ng/mL and 1.0 ± 0.6 ng/mL, respectively. The mean (range) biotin concentration for the donor samples pre- and post-treatment was 166 (15-1029)  ng/mL and 0.2 (<0.1-3)  ng/mL, respectively (P = 0.004).

CONCLUSIONS

These data demonstrate that treatment with VeraPrep Biotin™ does not affect analyte recovery in biotin-negative samples and effectively depletes both spiked and endogenous biotin in serum/plasma.

Global FT4 immunoassay standardization: an expert opinion review

OBJECTIVES

Results can vary between different free thyroxine (FT4) assays; global standardization would improve comparability of results between laboratories, allowing development of common clinical decision limits in evidence-based guidelines.

CONTENT

We summarize the path to standardization of FT4 assays, and challenges associated with FT4 testing in special populations, including the need for collaborative efforts toward establishing population-specific reference intervals. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. Further studies are needed to establish common reference intervals/clinical decision limits. Standardization of FT4 assays will change test results substantially; therefore, a major education program will be required to ensure stakeholders are aware of the benefits of FT4 standardization, planned transition procedure, and potential clinical impact of the changes. Assay recalibration by manufacturers and approval process simplification by regulatory authorities will help minimize the clinical impact of standardization.

SUMMARY

Significant progress has been made toward standardization of FT4 testing, but technical and logistical challenges remain.

OUTLOOK

Collaborative efforts by manufacturers, laboratories, and clinicians are required to achieve successful global standardization of the FT4 assays.

Human chorionic gonadotropin suspected heterophile interference investigations in immunoassays: a recommended approach

Background Heterophile antibody (HAb) interferences in immunoassays can cause falsely elevated hCG concentrations leading to incorrect diagnosis and treatments options. When results are not consistent with the clinical findings, hCG HAb interference investigation may be requested by the physician. A retrospective evaluation of the frequency of HAb interference was performed among cases of physician-requested investigations and the effectiveness of commercially available blocking reagents to detect HAb interference in two immunoassay systems was evaluated. Methods One hundred and thirteen physician requests for hCG HAb investigation from 2008 to 2017 were reviewed. The primary method used to measure hCG was the Beckman Coulter Access Total βhCG (2008-2010) and the Roche Elecsys HCG+β (2014-2017). HAb investigation included measurement by two immunoassays before and after treatment of samples with heterophile blocking reagents and serial dilution studies. Results Five cases of HAb and HAb-like interference were identified. The interference frequency was 6.7% for the Beckman assay and 2.9% for the Roche assay. The presence of HAb was detected using heterophile blocking reagents and an alternative method in three cases. The other two cases were detected due to discrepant results with an alternative method and non-linear serial dilutions (HAb-like). Conclusions HAb interference was observed in the Beckman and the Roche assays. The heterophile blocking reagents failed to detect 40% of interference cases. Blocking reagents should not solely be used for these investigations. Multiple strategies including the use of serial dilutions and using an alternative platform are critical when troubleshooting interferences in hCG immunoassays.

Analytical Evaluation of BioRad D-100 HPLC Analyzer and Workflow Comparison to BioRad TurboLink Variant II HPLC With Reflex to Boronate Affinity

Introduction

Measurement of hemoglobin A1c (HbA1C) is used for the diagnosis and management of patients with diabetes. Methods for measuring HbA1C are classified on the basis of charge differences (cation exchange chromatography) or structural differences (boronate affinity chromatography). Some cation exchange high-performance liquid chromatography (HPLC) analyzers may be prone to interferences from hemoglobin variants. Historically, our lab used two methods to report HbA1C results: cation exchange HPLC (VariantII) with reflex to boronate affinity HPLC (Ultra2) methods. A new analyzer (BioRad D-100) with improved interference detection and thresholds for interference was evaluated. The objectives of this study were (1) assess the comparability of HbA1c results between D-100, VariantII, and Ultra2; (2) evaluate the need for maintaining a reflex method; and (3) calculate cancellation rates before and after implementing D-100.

Methods

HbA1c was measured by cation exchange methods using VariantII Turbolink, D-100 (BioRad), and boronate affinity using Ultra2Affinity (Trinity Biotech) according to the manufacturer’s recommendations with the following analytical measuring ranges (AMRs), 4.0% to 17.6%, 4.0% to 18.0%, and 4.0% to 17.6%, respectively. D-100 was compared to VariantII (n = 26) and Ultra2 (n = 31) using residual patient samples from provider-ordered HbA1c having no chromatography flags and with the following chromatography flags on VariantII (n = 113): variant window (n = 41), HbA1c <4.0% (n = 24), HbA1a + HbA1b >5% (n = 19), HbF >5% (n = 9), P3 >10% (n = 6), HbA1c >17.6% (n = 4), unknown peak (n = 3), labile 5% to 15% (n = 3), labile >15% (n = 3), and HbS >60% (n = 1). The cancelation rates were calculated at baseline (January 1-31, 2018) and postimplementation of D-100 (September 20, 2018, to January 22, 2019).

Results

HbA1c results from D-100 were within ±0.3 or 5% with the following frequencies: Ultra2 in 96.2% (25/26) with VariantII in 96.8% (30/31) using samples with no chromatography flags. A total of 113 samples with abnormal VariantII flags were tested using D-100 with 82% (n = 92) not exceeding interference limits for result reporting. These D-100 results were within ±0.3 or 5% of Ultra2 results with the following frequencies: 38.5% (10/26) of samples below (n = 23) or above (n = 3) the AMR, 85.3% (29/34) of results with Hb variant flags, 68.0% (17/25) with unknown/minor peaks, and 71.4% (5/7) with HbF <15%. The clinical concordance was also assessed according to the following decision limits: normal <5.6%, prediabetic = 5.7% to 6.4%, and diabetic >6.5%. Results were concordant in 88% with variant peaks (12/13 w/HbA1c <5.6%, 8/11 w/HbA1c = 5.7%-6.4%, 10/10 w/HbA1c >6.5%), 84% with minor peaks (5/6 w/HbA1c <5.6%, 0/2 w/HbA1c = 5.7%-6.4%, 16/17 w/HbA1c >6.5%), and 86% with HbF (3/3 w/HbA1c <5.6%, 2/3 w/HbA1c = 5.7%-6.4%, 1/1 w/HbA1c >6.5%). Results above/below AMR had 100% concordance (>16.0% or <4.4%). The frequency of VariantII rule violation was 2.1% in January 2018, with 53 of 117 having results confirmed as <4.0% or >16.0% by Ultra2, 2 of 117 reported by Ultra2, and 62 being cancelled due to HbF >15% (n = 23) or variant Hb >60% (n = 39). The frequency of rule violation using only D-100 since implementation was 2.2%.

Conclusion

Implementation of D-100 has removed the need for boronate affinity reflex testing and maintained similar cancellation rates.

Effect of pH on the Quantification of Body Fluid Analytes for Clinical Diagnostic Testing

Background

Body fluid samples (BFs) with low pH have demonstrated underrecovery of enzyme activity. The aims of this study were (1) measure the frequency of abnormal pH in BFs received for clinical chemistry testing, (2) calculate recovery of analytes in BFs undergoing pH titration, and (3) investigate the mechanism of pH interference.

Methods

Residual BFs submitted for physician-ordered testing to the Central Clinical Laboratory (Mayo Clinic) were utilized for this study. BFs were centrifuged 10 minutes (3,200 rpm) prior to pH measurement (pH meter, Accumet X15; Fisher Scientific) and analysis. A Roche Cobas c501 (Roche Diagnostics) analyzer was used to measure amylase, lactate dehydrogenase (LDH), blood urea nitrogen (BUN), creatinine, glucose, albumin, total protein, bilirubin (all Roche Diagnostics reagents), and lipase (Sekisui Diagnostics). pH was measured in 122 BFs received between 10/23/2018 and 10/26/2018 within 24 hours of receipt. pH titration was performed using pooled BFs of similar source/type. Each pool was titrated over a range of pH (≤2 to ≥10) in 1-unit increments by addition of a fixed volume of acid (6M HCL) or base (6M NaOH). Analytes were measured before and after acid/base addition. Average percent recovery was calculated (measured/expected × 100%) from n = 3 to 9 pH measurements. A low pH BF pool was spiked (<5% by volume) with a high-concentration BF to investigate mechanism of enzyme underrecovery. Additionally, low pH BF pool was neutralized by addition of base and % recovery calculated. For all titration/spiking experiments, a control sample having the same volume of diluent (7% bovine serum albumin or saline) was used to account for the effects of dilution.

Results

BFs received (n = 122) had mean (SD) pH = 8.0 (0.6) with 6.6% (n = 8) having pH <7.0 and 2.5% (n = 3) having pH <6.0. All recovery (%) and pH data are expressed as mean (range) values. Amylase recovery (initial pH = 8.4-8.9) was 1.3 (0.9-2.2)% at pH = 1.6 (1.0-2.2) (n = 6), 55.6 (37.4-67.0)% at pH = 4.4 (3.5-5.4) (n = 6), 81.4 (74.0-85.2)% at pH = 6.2 (6.1-6.5) (n = 3), 90.1 (84.4-95.4)% at pH = 7.5 (7.3-7.7) (n = 3), 98.8 (96.2-101.7)% at pH = 10.0 (9.8-10.2) (n = 3), and 14.5 (1.4-38.9)% at pH = 11.9 (11.5-12.1) (n = 3). LDH recovery (initial pH = 8.2-8.5) was 1.4 (0.1-3.7)% at pH = 1.7 (1.0-2.4) (n = 6), 18.3 (0.5-39.7)% at pH = 4.5 (3.5-5.4) (n = 6), 63.6 (54.9-68.4)% at pH = 6.2 (6.1-6.5) (n = 3), 85.9 (80.2-90.7)% at pH = 7.2 (6.8-7.4) (n = 3), 46.1 (36.4-61.0)% at pH = 10.0 (9.8-10.2) (n = 3), and 9.8 (0.0-28.9)% at pH = 11.3 (10.4-12.1) (n = 3). Lipase recovery (initial pH = 8.2-8.9) was 10.4 (<1-18)% at pH = 1.8 (1.0-2.4) (n = 6), 73.9 (62.6-85.5)% at pH = 4.2 (3.4-5.2) (n = 3), 92.4 (90.8-93.5)% at pH = 6.2 (6.0-6.5) (n = 3), 96.3 (95.6-96.8)% at pH = 7.3 (6.8-7.7) (n = 3), and 92.9 (89.3-96.8)% at pH = 9.9 (9.8-10.1) (n = 3) and 80.9 (0.0-78.6)% at pH = 11.3 (10.4-12.1) (n = 3). Creatinine, BUN, albumin, glucose, total protein, and bilirubin recovery were 97.9 (92.2-102.9)%, 100 (96.6-103.1)%, 99.9 (97.6-102.4)%, 100.2 (97.8-103)%, 100.2 (98.7-101.9)%, and 100.1 (92.-105.9)%, respectively, between pH 1.3-11.7 (n = 9). Recovery of amylase, LDH, or lipase was <1% after spiking enzymes into BF pool with pH <3. pH adjustment to normal (pH = 8.6-9.0) also resulted in recovery of <1%.

Conclusion

Enzyme activity in BFs was not affected (90%-110% recovery) when pH = 7.4-8.5 for LDH, pH = 7.3-10.2 for amylase, pH = 6.0-9.9 for lipase, and pH = 1.3-11.7 for all other analytes. An irreversible loss of enzyme activity occurs at low pH. Few clinical BFs have pH <7.0, but laboratories should have awareness.

Reference Intervals: Comparison of Calculation Methods and Evaluation of Procedures for Merging Reference Measurements From Two US Medical Centers

OBJECTIVES

To analyze consistency of reference limits and widths of reference intervals (RIs) calculated by six procedures and evaluate a protocol for merging intrainstitutional reference data.

METHODS

The differences between reference limits were compared with "optimal" bias goals. Also, widths of the RIs were compared. RIs were calculated using Mayo-SAS quantile, EP Evaluator, and four International Federation of Clinical Chemistry and Laboratory Medicine methods: parametric and nonparametric (NP) with and without latent abnormal values exclusion (LAVE). Regression parameters from cotested samples were evaluated for harmonizing intrainstitutional reference data.

RESULTS

Mayo-SAS quintile, LAVE(-)NP, and EP Evaluator generated similar RIs, but these RIs often were wider than RIs from parametric procedures. LAVE procedures generated narrower RIs for nutritional and inflammatory markers. Transformation with regression parameters did not ensure homogeneity of merged data.

CONCLUSIONS

Parametric methods are recommended when inappropriate values cannot be excluded. The nonparametric procedures may generate wider RIs. Data sets larger than 200 are recommended for robust estimates. Caution should be exercised when merging intrainstitutional data.

Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department

BACKGROUND

Several cases of biotin interference with laboratory testing have been reported in the literature. However, there are no publications discussing the extent of biotin use or plasma concentrations observed among the patient population. The objective of this study was to determine the prevalence of biotin consumption using two distinct methods: surveying the outpatient population using a questionnaire and quantifying biotin in plasma samples collected from patients presenting to the Emergency Department (ED).

METHODS

Survey questionnaires (n = 4000) were distributed to Mayo Clinic outpatients over one week (July 10-14, 2017). Biotin was quantified in residual waste plasma samples collected for physician-ordered electrolyte panels from patients presenting to the ED (March 6-12, 2017 and March 26-April 4, 2017, n = 1442 unique patient samples).

RESULTS

1944 patients (972 female, 963 male, 9 no answer) with a median (interquartile range) age of 62 (49-72) years returned completed questionnaires (48.6%). From the completed surveys, 7.7% (95% CI, 6.6-8.9%) indicated biotin use. Quantitation of biotin in plasma samples from ED patients (n = 1442) revealed that 7.4% (95% CI, 6.2-8.9%) had concentrations at or above the lowest known threshold (10 ng/mL) for biotin interference in Roche Diagnostics immunoassay tests.

CONCLUSIONS

According to our survey results, reported use of biotin was common. The range of biotin concentrations in ED patient samples highlights the magnitude of the biotin interference problem and identifies a population at risk for potential harm. These findings should guide laboratorians and clinicians in developing effective strategies to mitigate safety risks and in assessing biotin usage trends within their own patient populations.

Quality Control Practices for Chemistry and Immunochemistry in a Cohort of 21 Large Academic Medical Centers

OBJECTIVES

In the United States, minimum standards for quality control (QC) are specified in federal law under the Clinical Laboratory Improvement Amendment and its revisions. Beyond meeting this required standard, laboratories have flexibility to determine their overall QC program.

METHODS

We surveyed chemistry and immunochemistry QC procedures at 21 clinical laboratories within leading academic medical centers to assess if standardized QC practices exist for chemistry and immunochemistry testing.

RESULTS

We observed significant variation and unexpected similarities in practice across laboratories, including QC frequency, cutoffs, number of levels analyzed, and other features.

CONCLUSIONS

This variation in practice indicates an opportunity exists to establish an evidence-based approach to QC that can be generalized across institutions.

Assessing Quality Control Strategies for HbA1c Measurements From a Patient Risk Perspective

BACKGROUND

Current laboratory risk management principles emphasize the importance of assessing laboratory quality control (QC) practices in terms of the risk of patient harm. Limited practical guidance or examples on how to do this are available.

METHODS

The patient risk model described in a published laboratory risk management guideline was combined with a recently reported approach to computing the predicted probability of patient harm to produce a risk management index (RMI) that compares the predicted probability of patient harm for a QC strategy to the acceptable probability of patient harm based on the expected severity of harm caused by an erroneously reported patient result.

RESULTS

Measurement procedure capability and quality control performance for two instruments measuring HbA1c in a laboratory were assessed by computing the RMI for each instrument individually and for the laboratory as a whole.

CONCLUSIONS

This assessment provides a concrete example of how laboratory QC practices can be directly correlated to the risk of patient harm from erroneously reported patient results.

Errors of Classification With Potassium Blood Testing: The Variability and Repeatability of Critical Clinical Tests

OBJECTIVE

To understand the performance of a currently used clinical blood test with regard to the frequency and size of variation of the results.

PATIENTS AND METHODS

From November 29, 2012, through November 29, 2013, patients were recruited at 65 sites as part of a previously reported clinical trial (ClinicalTrials.gov Identifier: NCT01737697). Eligible outpatients who had been fasting for at least 8 hours underwent venous phlebotomy at baseline, 30 minutes, and 60 minutes to measure plasma potassium levels in whole blood using a point-of-care device (i-STAT, Abbott Laboratories). We analyzed the results to assess their variability and frequency of pseudohyperkalemia and pseudonormokalemia.

RESULTS

A total of 1170 patients were included in this study. Absolute differences between pairs of measurements from different time points ranged from 0 to 2.5 mmol/L, with a mean difference of 0.26 mmol/L. The mean percentage differences were approximately 5% with an SD of 5%. Approximately 12% of differences between repeated fasting potassium blood test results were above 0.5 mmol/L (33% of the normal range), and 20% of patients (234) had at least one difference greater than 0.5 mmol/L. In 44.0% of the patients with a hyperkalemic average value (true hyperkalemia) (302 of 686), at least one blood test result was in the normal range (pseudonormokalemia), and in 30.2% of the patients with a normal average value (146 of 484), at least one blood test result was elevated (pseudohyperkalemia).

CONCLUSION

Expected variability and errors exist with potassium blood tests, even when conditions are optimized. Pseudohyperkalemia and pseudonormokalemia are common, indicating a need for thoughtful clinical interpretation of unexpected test results.

Composition of single-step media used for human embryo culture

OBJECTIVE

To determine compositions of commercial single-step culture media and test with a murine model whether differences in composition are biologically relevant.

DESIGN

Experimental laboratory study.

SETTING

University-based laboratory.

ANIMAL(S)

Inbred female mice were superovulated and mated with outbred male mice.

INTERVENTION(S)

Amino acid, organic acid, and ions content were determined for single-step culture media: CSC, Global, G-TL, and 1-Step. To determine whether differences in composition of these media are biologically relevant, mouse one-cell embryos were cultured for 96 hours in each culture media at 5% and 20% oxygen in a time-lapse incubator.

MAIN OUTCOME MEASURE(S)

Compositions of four culture media were analyzed for concentrations of 30 amino acids, organic acids, and ions. Blastocysts at 96 hours of culture and cell cycle timings were calculated, and experiments were repeated in triplicate.

RESULT(S)

Of the more than 30 analytes, concentrations of glucose, lactate, pyruvate, amino acids, phosphate, calcium, and magnesium varied in concentrations. Mouse embryos were differentially affected by oxygen in G-TL and 1-Step.

CONCLUSION(S)

Four single-step culture media have compositions that vary notably in pyruvate, lactate, and amino acids. Blastocyst development was affected by culture media and its interaction with oxygen concentration.