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.

Short- and Long-Term Biological Variability of Small Dense LDL, HDL3, and Triglyceride-Rich Lipoprotein Cholesterol.

BACKGROUND: Measurement of cholesterol within lipoprotein subfractions may aid in cardiovascular disease prediction. Simple, homogenous enzymatic assays for the direct measurement of lipoprotein subfractions have been developed to measure small dense low-density lipoprotein cholesterol (sdLDL-C), high-density lipoprotein-3 cholesterol (HDL3-C), and triglyceride-rich lipoprotein (TRL-C) cholesterol. The objective of this study was to determine biological variability for sdLDL-C, HDL3-C, and TRL-C in a healthy reference population to facilitate interpretation of these analytes. METHODS: Serum samples were collected from 24 healthy subjects (n = 14 female/10 male) daily for 3 days while non-fasting, and daily for 5 days, weekly for 4 weeks, and monthly for 6 months after overnight fasting. sdLDL-C, HDL3-C, and TRL-C cholesterol were measured by homogenous enzymatic assays. Sources of variability (between-subject, within-subject, and analytical) were calculated using random-effects regression models. Reference change value (RCV) and index of individuality (II) for each time period were determined from the variance components. RESULTS: Analytic variability (daily, weekly, and monthly CVA) was <3% for each analyte. Monthly within-subject variability (CVI) was 17.1% for sdLDL-C, 7.4% for HDL3-C, and 25.7% for TRL-C. Most of the monthly variation was attributed to between-subject variation for all 3 analytes. Overall RCVs for monthly measurements were 18.1 mg/dL for sdLDL-C, 6.1 mg/dL for HDL3-C, and 16.0 mg/dL for TRL-C. IIs were <0.6 for sdLDL-C and HDL3-C, and 0.81 for TRL-C. CONCLUSIONS: sdLDL-C, HDL3-C, and TRL-C showed moderate within-subject variability, but high between-subject variability, in a healthy reference population. Given the high individuality of each analyte, population-based reference intervals may be inadequate to detect clinically significant changes.

Limited Correlation between SARS-CoV-2 Serologic Assays for Identification of High-Titer COVID-19 Convalescent Plasma Using FDA Thresholds.

In August 2020, the Food and Drug Administration (FDA) Emergency Use Authorization (EUA) for COVID-19 convalescent plasma (CCP) specified 12 authorized serologic assays and associated assay-specific cutoff values for the selection of high-titer CCP for use in hospitalized patients. The criteria used for establishing these cutoff values remains unclear. Here, we compare the overall agreement and concordance of five serologic assays included in the August 2020 FDA EUA at both the manufacturer-recommended qualitative cutoff thresholds and at the FDA-indicated thresholds for high-titer CCP, using serum samples collected as part of the CCP Expanded Access Program (EAP). The qualitative positive percent agreement (PPA) across assays ranged from 92.3% to 98.8%. However, the high-titer categorization across assays varied significantly, with the PPA ranging from 26.5% to 82.7%. The Roche anti-NC ECLIA provided the lowest agreement compared to all other assays. Efforts to optimize high-titer cutoffs could reduce, although not eliminate, the discordance across assays. The consequences of using nonstandardized assays are apparent in our study, and the high-titer cutoffs chosen for each assay are not directly comparable to each other. The generalized findings in our study will be relevant to any future use of convalescent plasma for either COVID-19 or future pandemics of newly emerged pathogens. IMPORTANCE COVID-19 convalescent plasma (CCP) was one of the first therapeutic options available for the treatment of SARS-CoV-2 infections and continues to be used selectively for immunosuppressed patients. Given the emergence of novel SARS-CoV-2 variants which are resistant to treatment with available monoclonal antibody (MAb) therapy, CCP remains an important therapeutic consideration. The FDA has released several emergency use authorizations (EUA) that have specified which serological assays can be used for qualification of CCP, as well as assay-specific cutoffs that must be used to identify high-titer CCP. In this study, a cohort of donor CCP was assessed across multiple serological assays which received FDA EUA for qualification of CCP. This study indicates a high degree of discordance across the assays used to qualify CCP for clinical use, which may have precluded the optimal use of CCP, including during clinical trials. This study highlights the need for assay standardization early in the development of serological assays for emerging pathogens.

The Biological Variability of Plasma Ceramides in Healthy Subjects.

BACKGROUND: Ceramides are bioactive lipid species that mediate numerous cell-signaling events. Elevated plasma ceramides concentration constitutes a risk factor for several pathologies. Multiple studies have affirmed the plasma concentrations of 4 specific ceramides (Cer16:0, Cer18:0, Cer24:0, and Cer24:1) can predict cardiovascular disease risk. Furthermore, these ceramides can be altered by many lipid-lowering therapies. Understanding the biological variability within an individual, and within a population, will further inform the clinical use of plasma ceramides as a biomarker. In this study, we aimed to define the intra- and interbiological variability of ceramides in a healthy reference population in a weekly and monthly manner. METHODS: Fasting plasma from 24 healthy adults was collected daily (5 days), weekly (4 weeks), and monthly (7 months). Ceramide concentrations were measured with liquid chromatography-mass spectrometry (LC-MS). For analysis, we used random-effects regression models to estimate variance components. RESULTS: The analytical variability was smaller compared to the biological variability overall. The greatest variation reported was between-subject variation for all ceramide species. The critical difference-reference change value (RCV) for within-subject variations monthly were 0.07 mcmol/L (Cer16:0), 0.04 mcmol/L (Cer18:0), 1.09 mcmol/L (Cer24:0), and 0.27 mcmol/L (Cer24:1). The index of individuality (IOI) of ceramides were 0.82 (Cer16:0), 0.96 (Cer18:0), 1.06 (Cer24:0), and 0.89 (Cer24:1). The most consistent ceramide species was Cer18:0 with the lowest within- and between-subject critical differences in weekly and monthly measurements. CONCLUSIONS: Overall, this study demonstrates that the variability of ceramide concentrations at different time points is minimal within individuals, allowing a single draw to be sufficient at least in a yearly time frame.

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.

SARS-CoV-2 Serologic Assays Dependent on Dual-Antigen Binding Demonstrate Diverging Kinetics Relative to Other Antibody Detection Methods.

Longitudinal studies assessing durability of the anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) humoral immune response have generated conflicting results. This has been proposed to be due to differences in patient populations, the lack of standardized methodologies, and the use of assays that measure distinct aspects of the humoral response. SARS-CoV-2 antibodies were serially measured in sera from a cohort of 44 well-characterized convalescent plasma donors over 120 days post-COVID-19 symptom onset, utilizing eight assays, which varied according to antigen source, the detected antibody isotype, and the activity measured (i.e., binding, blocking, or neutralizing). While the majority of assays demonstrated a gradual decline in antibody titers over the course of 120 days, the two electrochemiluminescence immunoassay Roche assays (Roche Diagnostics Elecsys anti-SARS-CoV-2 [qualitative, nucleocapsid based] and Roche Diagnostics Elecsys anti-SARS-CoV-2 S [semiquantitative, spike based]), which utilize dual-antigen binding for antibody detection, demonstrated stable and/or increasing antibody titers over the study period. This study is among the first to assess longitudinal, rather than cross-sectional, SARS-CoV-2 antibody profiles among convalescent COVID-19 patients, primarily using commercially available serologic assays with Food and Drug Administration emergency use authorization. We show that SARS-CoV-2 antibody detection is dependent on the serologic method used, which has implications for future assay utilization and clinical value.

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.

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.

Hypomagnesemia at the time of autologous stem cell transplantation for patients with diffuse large B-cell lymphoma is associated with an increased risk of failure.

Magnesium is an essential element that is involved in critical metabolic pathways. A diet deficient in magnesium is associated with an increased risk of developing cancer. Few studies have reported whether a serum magnesium level below the reference range (RR) is associated with prognosis in patients with diffuse large B cell lymphoma (DLBCL). Using a retrospective approach in DLBCL patients undergoing autologous stem cell transplant (AHSCT), we evaluated the association of hypomagnesemia with survival. Totally, 581 patients eligible for AHSCT with a serum magnesium level during the immediate pre-transplant period were identified and 14.1% (82/581) had hypomagnesemia. Hypomagnesemia was associated with an inferior event-free (EFS) and overall survival (OS) compared to patients with a serum magnesium level within RR; median EFS: 3.9 years (95% CI: 1.63-8.98 years) versus 6.29 years (95% CI: 4.73-8.95 years) with HR 1.63 (95% CI: 1.09-2.43, p = 0.017) for EFS, and median OS: 7.3 years (95% CI: 2.91-upper limit not estimable) versus 9.7 years (95% CI: 6.92-12.3 years) with HR 1.90 (95% CI: 1.22-2.96, p = 0.005) for OS months 0-12, respectively. These findings suggest a potentially actionable prognostic factor for patients with DLBCL undergoing AHSCT.

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.

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.

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.

Updated ferritin reference intervals for the Roche Elecsys® immunoassay.

Reference intervals (RI) for ferritin are the subject of some controversy, with indications that changes in lifestyle and demographics (e.g., obesity) have limited the validity of RIs established decades ago. Package insert RIs for the Roche Elecsys® immunoassay do not include expected values for pediatric (<17-20 years) or geriatric (>60 years) individuals; furthermore the female ranges were established in mostly premenopausal volunteers. To establish more robust RIs, we utilized 5 years of retrospective patient data from physician-ordered ferritin measurements and excluded results from patients with diagnoses known to affect ferritin concentrations. Ferritin results from 1438 unique patients aged 7 months to 91 years were included in the study. Continuous RIs were fitted for females (n = 951) and males (n = 487) as a function of age; these were then divided into clinically relevant sex-specific age breaks. RIs were established for pre-adolescent (<10 years), adolescent (10-17 years) and adult males, and for pediatric (<18 years), adult (18-50 years) and older (>50 years) females. Established RIs were verified using specimens obtained from healthy donors.

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.

Prevalence of Clinically Significant Differences in Sodium Measurements Due to Abnormal Protein Concentrations Using an Indirect Ion-Selective Electrode Method.

BACKGROUND: Indirect ion-selective electrode (ISE) is the primary method used to measure sodium in automated clinical laboratories and is susceptible to the electrolyte exclusion effect. Pseudohyponatremia due to hyperproteinemia can affect patient management. The aims of this study were to (a) establish the relationship between serum total protein (TP) concentration and the magnitude of the electrolyte exclusion effect on indirect ISE-measured sodium values (b) estimate the frequency at which TP concentrations outside the reference interval may impact indirect-ISE measured sodium values, and (c) determine whether clinical decision support (middleware) rules in the laboratory would be effective for detecting cases of pseudohyponatremia. METHODS: Residual waste serum specimens from physician-ordered TP testing were collected (n = 112). Sodium concentration was measured using indirect ISE (Cobas 8000, Roche Diagnostics) and direct ISE (ABL 825, Radiometer) methods. The difference in sodium concentration (Δ[Na+]) was calculated as follows: ([Na+]indirect-ISE - [Na+]direct-ISE). Retrospective TP results reported from July 31, 2013, to September 24, 2014, were stratified by ordering location and sodium and TP co-ordering rates were quantified. RESULTS: Δ[Na+] was inversely proportional to TP concentration (y = -1.29x + 8.6, R = -0.883). The average difference (SD, range) was -6.1(3.4, -16-0) mmol/L when TP >7.9 g/dL (>79g/L), with 69% of samples demonstrating differences ≥4.0 mmol/L. A majority of intensive care unit patients (81%) were hypoproteinemic (<6.3 g/dL, <63g/L). Only 10.9% of sodium test orders include an order for TP on the same collection. CONCLUSIONS: Indirect sodium measurement is impacted when TP concentrations are increased. TP concentration outside the reference interval is prevalent and sodium is usually not ordered with TP. Health systems need to be aware of the limitations of their indirect-ISE method for sodium measurement.

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 ßhCG (2008-2010) and the Roche Elecsys HCG+ß (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.

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.