Utility of Commercially Available Quantitative hCG Immunoassays as Tumor Markers in Trophoblastic and Non-Trophoblastic Disease.

BACKGROUND: The use of quantitative human chorionic gonadotropin (hCG) as a tumor marker is widely accepted despite lack of FDA-approval for oncology. Differences in iso- and glycoform recognition among hCG immunoassays is well established, exhibiting wide inter-method variability. Here, we assess the utility of 5 quantitative hCG immunoassays for use as tumor markers in trophoblastic and non-trophoblastic disease. METHODS: Remnant specimens were obtained from 150 patients with gestational trophoblastic disease (GTD), germ cell tumors (GCT), or other malignancies. Specimens were identified by review of results from physician-ordered hCG and tumor marker testing. Five analyzer platforms were used for split specimen analysis of hCG: Abbott Architect Total, Roche cobas STAT, Roche cobas Total, Siemens Dimension Vista Total, and Beckman Access Total. RESULTS: Frequency of elevated hCG concentrations (above reference cutoffs) was highest in GTD (100%), followed by GCT (55% to 57%), and other malignancies (8% to 23%). Overall, the Roche cobas Total detected elevated hCG in the greatest number of specimens (63/150). Detection of elevated hCG in trophoblastic disease was nearly equivalent among all immunoassays (range, 41 to 42/60). CONCLUSIONS: While no immunoassay is likely to be perfect in all clinical situations, results for the 5 hCG immunoassays evaluated suggest that all are adequate for use of hCG as a tumor marker in gestational trophoblastic disease and select germ cell tumors. Further harmonization of hCG methods is needed as serial testing for biochemical tumor monitoring must still be performed using a single method. Additional studies are needed to assess the utility of quantitative hCG as a tumor marker in other malignant disease.

Evaluation of the automated LIAISON® SARS-CoV-2 TrimericS IgG assay for the detection of circulating antibodies.

OBJECTIVES: COVID-19 has brought about tests from many manufacturers. While molecular and rapid antigen tests are targeted for early diagnosis, immunoassays have a larger role in epidemiological studies, understanding longitudinal immunity, and in vaccine development and response. METHODS: The performance of the LIAISON® SARS-CoV-2 TrimericS IgG assay was evaluated against the Beckman ACCESS SARS-CoV-2 IgG assay in New Mexico, and against the Siemens ADVIA Centaur COV2G assay in New York. Discordant samples were parsed using a microneutralization assay. RESULTS: A SARS-CoV-2 antibody positivity rate of 23.8% was observed in the samples tested in New York (September 2020), while in the same month the positivity rate was 1.5% in New Mexico. Positive and negative agreement were 67.6% (95% CI 49.5-82.6%) and 99.8% (95% CI 99.5-99.9%), respectively, with the Beckman test, and 98.0% (95% CI 95.7-99.3%) and 94.8% (95% CI 93.4-96.0%), respectively, with the Siemens test. Receiver operating characteristic analysis for the detection of SARS-CoV-2 antibodies discloses an AUC, area under the curve, of 0.996 (95% CI 0.992-0.999) for the LIAISON® SARS-CoV-2 TrimericS IgG assay. The criterion associated to the Youden Index was determined to be >12.9 kAU/L with a sensitivity of 99.44% and a specificity of 99.82%. CONCLUSIONS: The LIAISON® SARS-CoV-2 TrimericS IgG assay is highly sensitive and specific. The balance of these parameters, without emphasis on high specificity alone, is particularly important when applied to high prevalence populations, where a highly sensitive assay will result in reporting a lower number of false negative subjects.

Recommendations for validation testing of home pregnancy tests (HPTs) in Europe.

Home pregnancy tests (HPTs) available in Europe include accuracy and other performance claims listed on their packaging. Due to the lack of guidance on the standardisation of such products, it is often difficult to replicate these claims when tested on a clinical sample, whether in a laboratory setting or by lay users. The In Vitro Diagnostic Regulation is a set of requirements that mandate comprehensive validation data on human pregnancy tests and other in vitro devices. It is due to replace the current European Directive (98/79/EC) and fully implemented in Europe by 2022. In June 2019, a panel of seven experts convened to discuss the validation studies required to provide the information needed to meet the new regulation for HPTs in Europe and proposed 15 recommendations for best practice. Defining best practice at all stages of validation of these important tests may ensure that tests marketed in Europe are fit for purpose, enabling lay users to be confident of the high quality of the HPT results they obtain. The panelists believe that the recommendations proposed here for the validation of HPTs may constructively contribute to improved standardisation of validation procedures in Europe.

Leveraging longitudinal clinical laboratory results to improve prenatal care.

OBJECTIVES: To assess the impact of providing laboratory-generated near-real-time clinical insights for pregnant Medicaid members to managed care organization (MCO) care coordinators. STUDY DESIGN: A prospective, nonrandomized feasibility study was conducted over 11 months to examine the benefits of laboratory-generated clinical insights on prenatal care quality metrics and clinical outcomes. Measures included early identification of pregnancy and births to facilitate care, care gaps with prenatal laboratory testing, emergency department (ED) visits, preterm births, and neonatal intensive care unit (NICU) admissions and length of stay. METHODS: Weekly MCO care coordinators were provided a laboratory-generated prenatal targeted intervention module (TIM) to supplement their existing systems in a longitudinal, patient-centric format. Care coordinators contacted patients for enrollment in prenatal or postpartum services based on the TIM, which identified concomitant health conditions, missing prenatal care, and risks. RESULTS: The prenatal TIM identified 1355 pregnant members, 77% (n = 1040) of whom were detected in the first trimester. A total of 488 births were identified within 24 hours of parturition. Sixty-four percent of women had at least 80% of prenatal care gaps associated with laboratory testing closed. Women with ongoing prenatal care had fewer ED visits (17% vs 23%) and NICU admissions (11% vs 18%) compared with those without prenatal care. After adjusting for confounders, ongoing prenatal care had a borderline effect at decreasing the probability of having an ED visit and a NICU admission. CONCLUSIONS: An innovative collaboration between an MCO and a clinical laboratory improved quality measures for prenatal members enrolled in Medicaid.

Correlation of SARS-CoV-2 Neutralizing Antibodies to an Automated Chemiluminescent Serological Immunoassay.

INTRODUCTION: Neutralizing antibodies (NAbs) are capable of binding to a virus to render it incapable of infection. The ability of commercially available SARS-CoV-2 serological tests to detect NAbs has not been widely reported. We sought to correlate the antibodies detected by an automated chemiluminescent immunoassay with NAbs. METHODS: Residual serum samples from 35 patients that had a positive antibody test using the LIAISON® SARS-CoV-2 S1/S2 IgG chemiluminescent immunoassay and 2 antibody-negative control sera were tested for NAbs using a plaque reduction neutralization test (PRNT). RESULTS: NAbs were detected in 66% (23/35) of the antibody-positive samples. The immunoassay signal value ranged from 21.7 to 131.3 AU/mL (median, 90.5) with significant correlation between it and the PRNT (r = 0.61, P = 0.002). In the samples without NAbs, the immunoassay signal ranged from 16.3 to 66.2 AU/mL (median, 27.2). An immunoassay signal cutoff of >41 AU/mL was 91% sensitive and 92% specific for the detection of NAbs. DISCUSSION: It is important that correlates of immunity to SARS-CoV-2 be identified and NAbs are considered to be central indicators of such. PRNT is the gold-standard test for identifying NAbs but it cannot be used for large-scale testing of populations. It is necessary to establish relationships between it and widely used commercial serological assays for SARS-CoV-2.

Current Practices When Reporting Quantitative Human Chorionic Gonadotropin Test Results.

BACKGROUND: Quantitative human chorionic gonadotropin (hCG) tests are commonly used to determine a woman's pregnancy status. Discrete results are evaluated and/or interpreted against a reference interval or cutoff. Reporting practices across laboratories have not been investigated. METHODS: A voluntary questionnaire was distributed to 6433 laboratories participating in a general chemistry proficiency testing survey. RESULTS: Responses were received from 3568 (55%) laboratories. Overall, 31% used a single reference cutoff, with 42% and 14% using values of 5.0 and 25.0 IU/L, respectively. In total, 68% of laboratories provided result interpretations, most frequently "negative" and "positive." Reference intervals based on chronological age were offered by 9% of laboratories; 60% reported gestational age-based intervals. In addition, 25% provided male-specific reference intervals, with 2.0 IU/L being the most commonly used single-point cutoff. Only 12% of laboratories offered a separate, orderable test for hCG as a tumor marker, with 5.0 IU/L as the most frequently used reference threshold. Nearly half of laboratories used assay product insert data as the reference interval source. CONCLUSIONS: There is wide variation when reporting quantitative hCG results. Despite a well-established reference limit of <5.0 IU/L for nonpregnant women, fewer than half of laboratories used this cutoff. The reporting of gestational age-based reference intervals is more common than those based on chronological age despite greater clinical utility for the latter. Data-driven guidelines for reporting quantitative hCG test results could deliver more consistent result interpretation.

Development of an Automated Enzymatic Method to Quantify Pyruvate Kinase in Red Blood Cells.

BACKGROUND: Pyruvate kinase (PK) deficiency is the most common cause of nonspherocytic hemolytic anemia owing to defective glycolysis. This study developed and validated an automated method to measure PK activity in red blood cells (RBCs). METHODS: PK catalyzes the reaction of phosphoenolpyruvate with ADP to form pyruvate and ATP. The pyruvate is reduced in the presence of lactate dehydrogenase and NADH to produce lactate and NAD+. The rate of absorbance decrease at 340 nm is proportional to PK activity. PK and hemoglobin (Hb) measurements were performed on a Roche cobas c501 analyzer. After establishing a k-factor, accuracy, linearity, imprecision, sensitivity, and stability were validated and the reference interval was verified. RESULTS: The k-factor was -9477. Accuracy was evaluated by method comparison (n = 56). Linear regression yielded y = 1.0x - 0.57, and R2 of 0.93. Linearity was determined by combining a high sample with hemolyzing solution in 6 different ratios. Linear regression analysis yielded y = 1.02x - 2.68, and R2 of 1.0. The assay was linear to 87 U/dL. Precision was evaluated by testing hemolysates in 3 replicates/day for 10 days. Within-run imprecision was 1.9% and 2.5% and total imprecision was 4.0% and 5.6% at 14.0 and 8.1 U/g Hb, respectively. The limit of blank was 0.0, and the limit of detection was 1.0 U/dL. Stability was determined in 4 sample types at 3 different temperatures; the changes were all <10% when compared with t0. The current PK reference interval of 4.6 to 11.2 U/g Hb was verified. CONCLUSIONS: This automated assay for quantifying PK in RBCs has acceptable performance characteristics and is fit for intended use.

Development of an enzymatic assay to measure lactate in perchloric acid-precipitated cerebrospinal fluid.

BACKGROUND: Individuals with inherited deficiencies of the pyruvate dehydrogenase complex or the respiratory chain complex can have increased concentrations of cerebrospinal fluid (CSF) lactate. Such measurements are clinical useful when measured in conjunction with pyruvate in order to calculate the lactate:pyruvate (L:P) ratio, a useful surrogate of cytosolic redox status. CSF pyruvate is measured in a protein-free supernatant prepared by the addition of CSF to perchloric acid while lactate is measured in untreated CSF. Utilizing the same sample for both lactate and pyruvate measurements is desirable. OBJECTIVE: To develop a method to measure lactate in perchloric-acid precipitated CSF and validate the L:P ratio as calculated from the analysis of both analytes in the same sample. METHODS: Samples were prepared by the addition of 1 mL CSF to 2 mL 8% (w/v) cold perchloric acid, incubated on ice for 10 min, then centrifuged to obtain a protein-free supernatant. Lactate was measured by its oxidation to pyruvate and hydrogen peroxide using lactate oxidase and the absorbance of the resulting chromogen determined at 540 nm on a Roche cobas c501 chemistry analyzer. Method accuracy, linearity, imprecision and sensitivity were determined and a reference interval was verified. RESULTS: To assess accuracy, this method was compared to lactate determined in unaltered CSF at another laboratory using 41 specimens with lactate concentrations from 0.6-11.9 mmol/L. Linear regression produced a slope of 1.09 and y-intercept of 0.26 (R2 = 1.00). Recovery was performed by ad-mixes of a high lactate standard and a CSF pool in different ratios to create a set of 19 samples prior to preparing protein-free supernatants. Recovery was 94.6-100% (mean ±â€¯SD was 97.4 ±â€¯1.4%) at lactate concentrations of 2.68 to 12.63 mmol/L. Linearity was determined by combining two supernatants with low and high lactate concentrations in different ratios to create a set of six samples (0.15-12.70 mmol/L) that were tested in duplicate. Linear regression generated a slope of 1.01, y-intercept of -0.04 (R2 = 1.00). Precision was verified by analyzing quality control materials (acid-treated lactate standard) in 3 replicates each day for 5 days. Within-laboratory imprecision was 2.3% at 1.5 mmol/L and 1.5% at 10.5 mmol/L. The limit of blank was 0.05 mmol/L as determined by the mean added to three standard deviations determined from 10 replicates of perchloric-acid treated saline pool. The limit of detection was determined to be 0.12 mmol/L calculated from 10 replicates of a patient sample treated with perchloric-acid. The manufacturer's reference interval of 1.1-2.4 mmol/L was verified using 20 residual patient CSF samples. CONCLUSIONS: CSF lactate can be measured with accuracy and precision using the same perchloric-acid treated sample that is used for pyruvate.

Genotype-Phenotype Correlations of Glucose-6-Phosphate-Deficient Variants Throughout an Activity Distribution.

BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked disorder that may manifest as neonatal jaundice or acute hemolytic anemia. Quantitative assessment of G6PD activity in erythrocytes is required to definitively diagnose a deficiency. Most males and homozygous females have low enzyme activities, whereas heterozygous females may have a range of activities. We sought to examine G6PD genotype-phenotype associations to identify an activity cutoff above which G6PD deficiency is unlikely. METHODS: Ninety-five residual samples were randomly selected to represent the various regions of a G6PD activity distribution. DNA was isolated from the leukocyte fraction and sequenced using the Sanger method. ROC curves were used to establish cutoffs. RESULTS: Thirteen variant alleles were identified, including 1 not previously reported. In the very deficient activity range, we found males and homozygous females of both class II and III variants. In the deficient category, we found predominantly class III males and heterozygous females. The presumed deficient category contained class III and IV variants and nonvariants. An activity cutoff of <7.85 U/g hemoglobin (Hb) was 100% sensitive and 94% specific for identifying a G6PD-deficient male, and a cutoff of <8.95 U/g Hb was 90% sensitive and 82% specific for a deficient female. CONCLUSIONS: The observed activity groupings were not because of a particular variant class. Cutoffs to identify the presence of a deficiency variant for males and females may be useful when trying to decide whether to recommend genetic analysis.

AAT Phenotype Identification by Isoelectric Focusing.

Isoelectric focusing (IEF) electrophoresis is considered to be the gold standard test for determining an individual's AAT phenotype. IEF electrophoresis is a technique used to separate proteins by differences in their isoelectric point (pI). Testing is performed on serum that is applied to an agarose gel containing ampholytes which create a pH gradient ranging from 4.2 to 4.9. Variants of AAT are therefore separated from each other and, after visualization of the focused protein bands using immunochemical techniques, can be identified and an AAT phenotype determined.In this chapter we elaborate on IEF electrophoresis as it relates to AAT phenotyping, describe practical approaches to AAT variant identification, and discuss circumstances in which phenotype testing may be inaccurate.