Identifying and Eliminating Laboratory Contamination by Topical Testosterone Therapeutics.

Many prescription and over-the-counter drugs are available as topical formulations. Contamination of clinical laboratory workspaces by topical drugs may increase the risk of potential interference with diagnostic testing. An example of localized workspace contamination attributed to a topical hormonal drug (testosterone, T) is presented to highlight significant challenges in identifying and resolving this potential problem. Investigation included precision studies, instrument service and parts replacement, instrument replacement, airflow analysis, environmental dust sampling, and the development of customized methods for workspace monitoring and cleaning. Laboratory policies and procedures were also revised to minimize future risk.

Mitigation of Biotin Interference in Manual and Automated Immunoassays by Preconjugating Biotinylated Antibodies to the Streptavidin Surface as an Alternative to Biotin Depletion.

BACKGROUND: Streptavidin-to-biotin binding is one of the strongest noncovalent interactions in nature and incorporated into many immunoassays. Biotin-streptavidin coupling assays are susceptible to interference from free biotin in patient specimens, which may falsely decrease or increase results. To prevent biotin interference, we evaluated a method to preconjugate biotinylated antibodies to the assay's streptavidin solid surface before adding patient specimen and compared this technique to a biotin depletion protocol. METHODS: Biotin interference in 3 manual ELISAs and 2 automated immunoassays was established. Mitigation of biotin interference by preincubation was evaluated in each assay by adding biotinylated antibody to the streptavidin-coated surface before adding biotin- or PBS-spiked serum. Lastly, the preincubation method was compared to a biotin-depletion protocol to compare the effectiveness of mitigating biotin interference. RESULTS: In the presence of 400 µg/L biotin, analyte detection was reduced to 10% to 15% of total in the ELISA assays and to 15.2% in the automated sandwich (thyroglobulin) immunoassay. In the automated competitive (free thyroxine) immunoassay, biotin caused an increased detection of 551.6%. Preconjugation of the biotinylated capture antibody to the streptavidin surface in the ELISA assays resulted in 84% to 99% activity recovery, compared to 84% to 97% by a biotin depletion protocol. Similarly, automated sandwich and competitive immunoassays obtained 97.1% and 116.5% recovery by preconjugation, compared to 95.6% and 100.3% by the depletion method, respectively. CONCLUSION: This study demonstrates how assay redesign to include preconjugation of biotinylated capture antibody to streptavidin is an effective alternative to biotin-depletion methods to mitigate biotin interference.

Evaluation of an adenosine deaminase (ADA) assay in serum, pleural, pericardial, peritoneal, and cerebrospinal fluids on the Roche cobas c501 analyzer.

OBJECTIVES: Adenosine deaminase (ADA) can be increased in various body fluids during infectious and inflammatory states. The objective of this study was to evaluate the performance characteristics of the Diazyme ADA assay for serum, pleural, pericardial, peritoneal, and cerebrospinal fluids using the Roche cobas c501 analyzer. METHODS: Accuracy, linearity, recovery, precision, sensitivity, specificity, reference interval, and stability studies were conducted. Potential interference of hyaluronidase and ultracentrifugation pre-treatment for viscosity on ADA concentrations were further evaluated. RESULTS: Assay method comparison to two separate external laboratories showed the following results (slope, intercept, %bias): serum (1.053, -0.478, 4.4 %); pleural (1.046, -1.41, 2.6 %). Accuracy (109.6 % recovery) was further demonstrated using a commercially available ADA reference material (BCR647). Linearity and spiked recovery studies showed percent recoveries ranging 94.3-109.3 %. Precision across all specimen types was ≤4.7 %CV. Interference was observed with increasing concentrations of various sources of conjugated and unconjugated bilirubin. Reference intervals were established for serum and pleural fluids, and previously published reference intervals were verified for pericardial, peritoneal, and cerebrospinal fluids. All specimen types were stable for 24 h ambient (8-25 °C), 1 week refrigerated (2-8 °C), and 1 month frozen (-20 °C). Of the two types of hyaluronidase evaluated, one showed positive interference for ADA (Sigma-Aldrich, H3506; 4.59 to 17.90 average % difference from baseline). Ultracentrifugation did not interfere with results (-2.32 to 0.87 average % difference from baseline). CONCLUSIONS: The Diazyme ADA assay was validated for use in our laboratory for all fluid types evaluated. Interference was observed with increasing concentrations of bilirubin and one source of hyaluronidase.

Tobacco and Cannabis Use During Pregnancy.

OBJECTIVES: Nicotine (NIC) use during pregnancy can influence markers used in biochemical maternal serum screening. This study was designed to determine prevalence of disclosed tobacco smokers in our patient population and to compare disclosed tobacco smoking status with the presence of serum nicotine and a common tetrahydrocannabinol (THC) metabolite. METHODS: A deidentified dataset of disclosed smoking status for quadruple (Quad) screens was obtained. Residual serum submitted for Quad screens was obtained from frozen storage and analyzed for NIC and THC metabolites. RESULTS: Of specimens that had corresponding responses to the smoking history question on the patient history form, 7.2% (n = 1,783 of 24,611) specified that the patient was a tobacco smoker. Of the 271 specimens biochemically analyzed for NIC and THC metabolites, disclosed tobacco smokers had the highest prevalence of detectable NIC and THC metabolites. THC product use was most prevalent in patients categorized as probable tobacco smokers based on cotinine concentrations, as well as in younger patients. CONCLUSIONS: Prevalence and concentration of NIC and THC metabolites vary based on disclosed tobacco smoker status. Biochemical testing may increase sensitivity for the identification of NIC and THC status over self-reporting.

Pretreatment of Body Fluid Specimens Using Hyaluronidase and Ultracentrifugation.

OBJECTIVE: Viscous body fluids present challenges during clinical laboratory testing. The present study was conducted to evaluate the effectiveness of hyaluronidase (HYAL) and ultracentrifugation (UC) pretreatment for a variety of body fluids before clinical chemistry testing. METHODS: The following body fluids were evaluated: biliary/hepatic, cerebrospinal, dialysate, drain, pancreatic, pericardial, peritoneal/ascites, pleural, synovial, and vitreous. Analytes assessed included amylase, total bilirubin, cancer antigen 19-9, carcinoembryonic antigen, cholesterol, chloride, creatinine, glucose, lactate dehydrogenase, lipase, potassium, rheumatoid factor, sodium, total protein, triglycerides, urea nitrogen, and uric acid. RESULTS: Observed percentage differences between HYAL treated and untreated fluids were less than ±15% for all analytes investigated, with a small number showing statistical significance (P <.05). In addition, UC showed increased variability for limited body fluid/analyte combinations. CONCLUSION: The HYAL treatment effectively reduced viscosity for body fluids. Validation of specimen pretreatment processes ensures acceptable analytical performance and the absence of unanticipated interferences.

Plasma hemoglobin: A method comparison of six assays for hemoglobin and hemolysis index measurement.

INTRODUCTION: Plasma hemoglobin (Hb) is measured for assessment of in vivo and in vitro hemolysis. The objective of the present investigation was to conduct a method comparison of five quantitative and one semi-quantitative Hb and H-index (hemolysis index) assays to evaluate their performance measuring plasma Hb in clinical specimens. METHODS: One hundred and fourteen clinical specimens previously tested for plasma Hb using a laboratory-developed spectrophotometric assay were also tested for Hb using a HemoCue Plasma/Low Hb assay (azide methemoglobin), a laboratory-modified Pointe Scientific Hb assay (cyanmethemoglobin), tested for H-index measurements using a Roche cobas c501, an Abbott Architect c8000, and a semi-quantitative (binned) H-index measurement on a Beckman AU5800. The reference result was defined as the median Hb score (median of all Hb or H-index results). RESULTS: The laboratory-developed spectrophotometric Hb assay and Roche H-index methods mostly closely matched the median Hb score across all data, as well as for lower range median Hb score results ≤2.0 g/L. Two-way frequency table analysis using an Hb (or H-index) cutoff of 0.5 g/L (or 0.5 H-index units) was then performed to compare methods to the median Hb score cutoff. The Beckman method had the highest accuracy at this cutoff, the Roche and Abbott methods had the highest positive predictive value (PPV), and the Beckman, HemoCue, and Pointe methods had the highest negative predictive value (NPV). CONCLUSIONS: Plasma Hb and H-index results vary by method. Laboratories should evaluate the performance characteristics of their respective assays when considering adoption of spectrophotometric or chemical methods for plasma Hb assessment.

Excessively low cholesterol and triglyceride levels in an apparently healthy patient.

Lipid panels are a commonly performed test in clinical laboratories. Due to the high prevalence of cardiovascular diseases around the world, it is common to see serum or plasma specimens with high results for one or more components of the lipid panel. Exceedingly low results, however, are rare and may be attributed to certain genetic, infectious, or autoimmune conditions in addition to analytical interference. Here we report a serum specimen from a 58-year-old female with cholesterol and triglyceride values below the detection limit of the assay, which was investigated to identify the cause of the anomaly. Using vitamin C test strips and high-performance liquid chromatography, the presence of high levels of antioxidant vitamin C in the patient specimen was confirmed. Subsequent treatment of the sample with the enzyme ascorbate oxidase inactivated vitamin C, leading to lipid analyte values falling within the expected range upon repeat analysis. Thus, analytical interference by vitamin C should be considered when suspiciously low lipid panel results are encountered.

Evaluation of 3 SARS-CoV-2 IgG Antibody Assays and Correlation with Neutralizing Antibodies.

BACKGROUND: As serologic assays for SARS-CoV-2 become more widely utilized, it is important to understand their performance characteristics and correlation with neutralizing antibodies. We evaluated 3 commonly used SARS-CoV-2 IgG assays (Abbott, DiaSorin, and EUROIMMUN) for clinical sensitivity, specificity, and correlation with neutralizing antibodies, and then compared antibody kinetics during the acute phase of infection. METHODS: Three panels of samples were tested on every assay. Sensitivity was assessed using a panel of 35 specimens serially collected from 7 patients with RT-PCR-confirmed COVID-19. Specificity was determined using 100 sera samples collected in 2018 from healthy individuals prior to the outbreak. Analytical specificity was determined using a panel of 37 samples from individuals with respiratory illnesses other than COVID-19. RESULTS: Clinical sensitivity was 91.43% (95% CI 76.94-98.20%) for Abbott, and 88.57% (95% CI 73.26-96.80%) for both DiaSorin and EUROIMMUN. Clinical specificity was 99.00% (95% CI 94.55-99.97%) for Abbott and DiaSorin and 94.00% (95% CI 87.40-97.77%) for EUROIMMUN. The IgG assays demonstrated good qualitative agreement (minimum of 94%) and good correlation between the quantitative result for each combination of assays (r2 ≥ 0.90). The neutralizing antibody response did not necessarily follow the same temporal kinetics as the IgG response and did not necessarily correlate with IgG values. CONCLUSION: The 3 IgG antibody assays demonstrated comparable performance characteristics. Importantly, a qualitative positive IgG result obtained with any of the assays was associated with the presence of neutralizing antibodies; however, neutralizing antibody concentrations did not correlate well with signal to cutoff ratios.

Laboratory evaluation of homocysteine remethylation disorders and classic homocystinuria: Long-term follow-up using a cohort of 123 patients.

The homocystinurias, caused by defects of remethylation and cystathionine-beta-synthase (CBS) deficiency, are characterized by elevated homocysteine and abnormal methionine levels. Various treatments, including injectable hydroxycobalamin and oral betaine, aim to reduce homocysteine toxicity and normalize methionine, but only limited biochemical data has been reported assessing biochemical response to treatment. We analyzed laboratory results in 812 plasma samples from 56 patients with remethylation disorders and 67 patients with CBS deficiency. Total plasma homocysteine (tHcys) decreased with therapy, but rarely normalized regardless of treatment, with highest levels seen in CBS (116 ±â€¯79 µmol/L) and MTHFR (102 ±â€¯56 µmol/L) deficiencies. In CBS deficiency, tHcys correlated positively with methionine (rs = 0.51, p < 0.0001) and inversely with cystine (rs = -0.57, p < 0.0001) consistent with a metabolic block downstream of homocysteine. In patients with remethylation disorders, methionine was mostly normal on therapy, and inversely correlated with tHcys (rs = -0.57, p < 0.0001) demonstrating effectiveness of hydroxycobalamin and/or betaine in stimulating tHcys remethylation. Betaine also significantly increased sarcosine from its pre-treatment level on average 19-fold in remethylation disorders and 3-fold in CBS deficiency, with sarcosine > 5 µmol/L being 97% sensitive and 95% specific for betaine therapy. These results show that existing therapies improve sulfur amino acid metabolism without completely normalizing it and that sarcosine can determine compliance to betaine supplementation.

Intermethod differences in results for total PSA, free PSA, and percentage of free PSA.

Serum prostate-specific antigen (PSA) assays differ in calibration and response to different PSA forms. We examined intermethod differences in total PSA (tPSA) and free PSA (fPSA) measurements. We tested 157 samples with tPSA concentrations of 2 to 10 ng/mL (2-10 microg/L) using 6 PSA/fPSA method pairs and 1 tPSA method: ADVIA Centaur (complexed and total; Siemens Diagnostics, Tarrytown, NY), ARCHITECT i 2000(SR) (Abbott Diagnostics, Abbott Park, IL), AxSYM (Abbott Diagnostics), IMMULITE 2000 (Siemens Diagnostics), Modular E170 (Roche Diagnostics, Indianapolis, IN), UniCel DxI 800 (Beckman Coulter, Brea, CA), and VITROS ECi (tPSA only; Ortho-Clinical Diagnostics, Raritan, NJ). Regression analysis was performed for PSA, fPSA, and percentage of fPSA with the ARCHITECT i 2000(SR) comparison method. Differences between test and comparison methods were estimated at 2.5, 4.0, and 10.0 ng/mL (2.5, 4.0, and 10.0 microg/L) for tPSA and 15%, 20%, and 25% for percentage of fPSA. Relative differences were more than 10% at 4.0 ng/mL (4.0 microg/L) tPSA for the Centaur, IMMULITE, ECi, and DxI methods. At 20% fPSA, the relative difference was more than 10% for all methods except the AxSYM. Additional harmonization is needed for tPSA and fPSA methods.

Performance characteristics of the AxSYM D-dimer assay.

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

Performance characteristics of the Access Inhibin A assay.

BACKGROUND: Second trimester maternal screening using AFP, uE3, hCG, and inhibin A has shown a detection rate for Down's syndrome of 81% with a 5% false positive rate. Inhibin A may also have utility as a serum tumor marker in postmenopausal women with ovarian cancer and men with testicular stromal tumors. METHODS: The Beckman Coulter Access Inhibin A assay was evaluated for limit of blank, dilution linearity, imprecision, interferences, reference intervals, and comparison to an inhibin A ELISA. RESULTS: The limit of blank was 0.1 ng/l. The assay was linear from 0.2 to 1347 ng/l. Total inter-assay CVs were <5% for control levels ranging from 24.6 ng/l to 811 ng/l. Interference studies showed recoveries of inhibin A within 10% of expected values at interferent concentrations of 10 g/l hemoglobin and 22 g/l triglycerides. No significant interference was observed at a bilirubin concentration of 400 mg/l. The 97.5th percentile upper reference limits were 6.8 ng/l for postmenopausal women and 3.0 ng/l for men. The Access assay compared to an ACTIVE ELISA showed a slope of 0.88, an intercept of -3.7 ng/l, S(y/x)=40 ng/l, and r=0.98. CONCLUSIONS: The analytical performance of the Access inhibin A assay is acceptable for routine laboratory testing.

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

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

Antibodies to small ubiquitin-like modifier activating enzyme are associated with a diagnosis of dermatomyositis: results from an unselected cohort.

The aim of this study was to examine the frequency and significance of antibodies targeting the small ubiquitin-like modifier 1 activating enzyme (SAE) in patients under serologic evaluation for idiopathic inflammatory myopathies. Patient sera (n = 17) recognizing bands at approximately 40 (SAE1) and 90 (SAE2) kDa were identified in 6445 consecutive samples for myositis autoantibody evaluation by immunoprecipitation (IP) of S35-labeled K562 cell lysate. All 17 positive samples, 176 disease, and 67 healthy controls were evaluated for SAE1 antibodies using a line immunoblot assay (LIA). Clinical data of SAE antibody-positive patients were obtained by retrospective chart review. Positivity with both methods was associated with a diagnosis dermatomyositis with characteristic skin manifestations of varying severity and muscle involvement. Majority of the patients were female (73.7%), mean age of 55.0 (range 12.0-82.0) years at the time of testing. Using the IP as reference, the SAE1 LIA had a sensitivity of 100% (95% CI 82.4-100%), specificity of 99.6% (95% CI 97.7-100%), positive predictive value of 95.0% (95% CI 75.1-99.9%), and negative predictive value of 100% (95% CI 98.5-100%). This study confirms the association of SAE antibodies in patients with dermatomyositis. A combination of IP and the LIA specific for SAE1 may be useful in antibody detection.

How low can you go? Analytical performance of five automated testosterone immunoassays.

BACKGROUND: Testosterone is commonly measured using immunoassays, yet concerns with the accuracy and quality of testing by these methods exist, particularly for low testosterone concentrations. Study objectives were to evaluate selective performance characteristics, including functional sensitivity (FS), of 5 automated immunoassays for total testosterone. METHODS: FS, imprecision, assay interference, limit of blank, linearity, and accuracy were assessed using the Abbott ARCHITECT i2000SR, SIEMENS ADVIA Centaur and IMMULITE 2000, Beckman Coulter DxI 800, and Roche MODULAR E170. Comparisons to an in-house liquid chromatography-tandem mass spectrometry (LC-MS/MS) method were performed using patient samples from men, women, boys, and girls. RESULTS: FS at 20% coefficient of variation (CV) for the ARCHITECT, Centaur, DxI, E170 and IMMULITE assays were 0.14, 1.23, 0.36, 0.77, 3.49 nmol/L, respectively. Total CVs for the 5-day imprecision study were ≤ 9.0% for all methods. All assays met manufacturer's claims for hemolysis, icterus, and lipemia interference and limit of blank. Dilution linearity studies had deviations from the target recoveries ranging from 3.4% (ARCHITECT) to 14.3% (DxI). Using National Institute of Standards and Technology Standard Reference Material 971, recoveries ranged from 79.2-149.2% (DxI, male and female, respectively). When compared to LC-MS/MS, more immunoassays under-recovered in men and women and over-recovered in boys and girls. Slopes ranged from 0.71 (IMMULITE, women) to 1.35 (DxI, boys). The combined average for percent bias was higher in boys (28.0%) than men (11.6%), women (22.8%), and girls (25.7%). CONCLUSIONS: Challenges with accurately measuring testosterone appear to remain for some immunoassays, but not all. While most immunoassays remain optimized for concentrations observed in healthy men, some showed acceptable performance when challenged at lower concentrations.

Lipemic interference of ceruloplasmin assays - An evaluation of lipid removal methods.

BACKGROUND: The present studies were conducted to characterize lipemic interference across three FDA-cleared ceruloplasmin (CERU) assays and to evaluate procedures designed to remove lipemic interference. METHODS: CERU assays on the Abbott ARCHITECT ci8200, Beckman AU5800, and Roche cobas Integra 400 Plus were evaluated. Precision, linearity with dilution, lipemic interference, and three methods for removing lipemia were assessed on each platform: ultracentrifugation (UC), lipemia-clearing reagent LipoClear (LC), and 1:5 dilution (DIL). Lipemia-index (L-index) thresholds were established using endogenously lipemic specimens and sera spiked with human-derived triglyceride-rich lipoproteins. RESULTS: The ci8200 showed greater susceptibility to endogenous lipemic interference than would be expected based on vendor-derived limits established with Intralipid. Endogenous lipemia causes a negative interference on the ci8200 and a positive interference on the Integra. UC was generally the most reliable method of removing lipemic interference without impacting baseline CERU results. CONCLUSIONS: CERU assays on different platforms have varying susceptibility to lipemic interference. L-index thresholds derived using Intralipid may not accurately represent interference caused by endogenous lipemia.

Performance characteristics of five automated CA 19-9 assays.

Serum concentrations of cancer antigen (CA) 19-9 can be useful in monitoring response to therapy in pancreatic cancer. The objective of this study was to evaluate 5 automated CA 19-9 assays: ARCHITECT 12000 (Abbott Diagnostics, Abbott Park, IL), ADVIA Centaur (Bayer Diagnostics, Tarrytown, NY), UniCel Dxl 800 (Beckman Coulter, Fullerton, CA), IMMULITE 2000 (Diagnostic Products, Los Angeles, CA), and Elecsys E170 (Roche Diagnostics, Indianapolis, IN). All methods were evaluated for limit of detection, linearity, imprecision, method comparison, and reference intervals. Limit of detection results were all below 2.0 kU/L and met the manufacturers' claims. Linearity had deviation from target values that ranged from 4.5% to 26.7%. All methods showed acceptable imprecision with total coefficients of variation less than 8%. Method comparison by Passing-Bablok analysis resulted in slopes ranging from 1.00 to 2.06 and correlation coefficients of 0.85 to 0.98. Between 97.6% and 99.2% of results from healthy volunteers were less than 35 kU/L. All methods show acceptable analytic performance.

Performance characteristics of 5 automated thyroglobulin autoantibody and thyroid peroxidase autoantibody assays.

BACKGROUND: Measurement of thyroid peroxidase autoantibodies (TPOAb) is useful in diagnosing patients with autoimmune thyroid disease. Measurement of thyroglobulin autoantibodies (TgAb) is used to detect potential interferences with thyroglobulin immunoassays and in limited situations for the diagnosis of autoimmune thyroid disease. METHODS: The limit of detection, imprecision, reference interval, method comparison and diagnostic concordance for the ADVIA Centaur, ARCHITECT i2000, AxSYM, Immulite 2000, Modular E170 (TPOAb only), and UniCel DxI 800 (TgAb only) methods were evaluated. The Advantage was used as the comparison method. RESULTS: Total imprecision ranged from 2.6% to 14.9% for TgAb and 2.1% to 15.8% for TPOAb. Passing-Bablok slopes ranged from 0.51 to 10.4 (TgAb) and 1.05 to 7.12 (TPOAb) with correlation coefficients of 0.48 to 0.82 (TgAb) and 0.66 to 0.78 (TPOAb). Assay cutoffs were adjusted using a common set of reference interval samples. Concordance with the Advantage assay using the new cutoffs was found to be improved and ranged from 68.5% to 84.7% (TgAb) and 77.5% to 84.7% (TPOAb). CONCLUSIONS: Although all assays generally performed well, assay concordance for a negative or positive result ranged from 54.2 to 84.7%. Quantitative agreement between methods was generally poor and methods could not be used interchangeably. Additional standardization efforts are required to improve inter-method agreement.

Performance characteristics of seven automated thyroxine and T-uptake methods.

BACKGROUND: Estimates of the free thyroxine concentration can be made using measurements of thyroxine (T4) and the thyroid hormone binding ratio (THBR, usually reported as T-uptake) according to the formula free thyroxine index (FTI)=T4xTHBR. We evaluated the performance characteristics of 7 pairs of automated T4 and T-uptake methods. METHODS: We evaluated the Architect i2000, AxSYM, ADVIA Centaur, UniCel DxI 800, Immulite 2000, Modular E170 and Vitros ECi methods for T4 and T-uptake. Imprecision was assessed by duplicate determinations on 3 levels of quality control material per run, 2 runs per day, on 5 separate days. Method comparison studies were performed with 205 patient samples and 68 samples from subjects in the second or third trimester of pregnancy. Results for both imprecision and method comparison were converted to the THBR as outlined by each method's manufacturer. RESULTS: Overall CVs for T4 and THBR methods were 3.2-8.9% and 1.2-6.7%, respectively. T4 methods generally agreed well. The THBR methods did not agree nearly as well. Comparison of FTI results with free T4 by equilibrium dialysis showed good correlation but different slopes. CONCLUSIONS: All methods show adequate precision but the THBR and FTI results are not well standardized.