A case of false-positive test results in a pregnant woman of unknown HIV status at delivery

A case of a false positive HIV antigen/antibody screen in a pregnant woman at delivery and the clinical importance of reviewing signal-to-cutoff ratio values

We present a unique case not previously touched upon in the literature, and its ensuing management, of a falsely reactive HIV (human immunodeficiency virus) screening test which resulted in a woman during active labor, hours after rupture of membranes. The patient was screened for HIV using the ARCHITECT 4th generation HIV 1 and 2 Antigen/Antibody (Ag/Ab) Combo assay, and the results were repeatedly reactive. A cesarean delivery was recommended, and the patient received intrapartum antiretroviral therapy. Due to rapid progression of labor, the infant was delivered vaginally and received multiple doses of antiretroviral therapy. For confirmation, a viral load PCR test was obtained which resulted undetectable, and it was concluded that the screening results were falsely positive. While the cause of the inaccurate screening result is still unclear, a COVID-19 vaccination in close proximity to the delivery remains suspicious. Four months after delivery, the patient's screening test was no longer reactive.

Falsely elevated thyroid hormone levels associated with fibrin interference in patients receiving oral anticoagulant therapy

OBJECTIVE

Unique clinical courses were observed in two asymptomatic patients receiving warfarin who referred to our hospital because of suspected central hyperthyroidism. We eventually diagnosed these patients with falsely elevated thyroid hormone levels caused by macroscopically invisible fibrin. Although false results caused by fibrin interference in vitro have been identified in various immunoassays, especially in blood samples from patients receiving anticoagulant therapy, no studies on thyroid function testing have been reported. The experience in evaluating these cases prompted us to investigate the independent influence of oral anticoagulants via putative fibrin interference on thyroid function testing.

METHODS

We retrospectively reviewed known contributing factors that affect thyroid function testing including age, gender, medication history, body mass index, estimated glomerular filtration rate, smoking status, alcohol consumption, and the seasons of hospital visits from participants who presented the Department of Health Checkup between April 2010 and December 2020.

RESULTS

A propensity-matched analysis revealed that the median serum free thyroxine levels under oral anticoagulant were significantly higher (17.9 pmol/L, n = 60) than those without anticoagulants (16.0 pmol/L, n = 60; p < 0.001). It was noted that this difference was the largest among contributing factors we analyzed. No significant differences were noted in serum thyroid-stimulating hormone levels.

CONCLUSIONS

We report two patients receiving warfarin with falsely elevated thyroid hormone levels caused by fibrin interference resembling central hyperthyroidism for the first time. Our retrospective study suggests that the medication status of oral anticoagulants should be considered when evaluating thyroid function tests.

Positive Anti-HIV ELISA Results in Pregnancy: Is It Reliable?

Background: Human immunodeficiency virus (HIV) can be transmitted from mothers to their babies during pregnancy, delivery through vaginal fluids or breastfeeding. As false positivity anti-HIV results due to pregnancy could be detected and no relevant study have been reported in Northern Cyprus so far, we aimed to estimate the false anti-HIV positivity rate in pregnant women. Methods: A total of 11.977 women admitted to Near East University Hospital between 2015 and 2018 were involved. The fourth generation anti-HIV-1/2 ELISA test was carried out by chemiluminescence enzyme immunoassay. Positive results were confirmed by real-time polymerase chain reaction (rt-PCR). SPSS (Statistical Package for the Social Sciences) Demo Ver 22 program was used for statistical analysis and significance (p<0.05) was measured by Person Chi-Square and Fisher's Exact tests. Results: Anti-HIV-1/2 ELISA test was positive in 7 (0.3%) of pregnant and 11 (0.1%) of non-pregnant women. HIV RNA was not detected in any pregnant however, was detected in 2 (0.02%) of non pregnant. S/Co titer of pregnant and non pregnant who have positive anti-HIV-test without viral load was x̄=2.68±1.64 (1.34-5.20) and x̄=8.63±7.68 (1.56-20.98) respectively. False positivity was significantly higher in pregnants compared to non-pregnants (p=0.033). Conclusion: False positivity can be encountered during pregnancy therefore, positive anti-HIV-1/2 ELISA results should be confirmed with molecular techniques before initiating antiretroviral treatment.

Application of case study to introduce medical students to molecular biology techniques used in HIV diagnostics

Diagnostic molecular biology is a fast developing discipline of laboratory medicine widely used in numerous medical branches such as oncology, hematology, immunology, internal medicine, or infectious diseases, which will certainly have a major impact on clinical medicine in the near future. Nowadays, educational process is forced to face the quickly growing overflow of easily accessible data and properly guide the students not to be lead astray in the information chaos. Hence, in view of the foregoing, it appears obvious that modern medical education should put particular stress on selective acquiring, interpreting, and applying integrated multidisciplinary knowledge rather than on just absorbing and memorizing huge amount of scattered information. The presented case study aims at familiarizing the students with basic molecular biology techniques such as enzyme-linked immunosorbent assay, Western blot, and quantitative reverse transcription-polymerase chain reaction. Importantly, it is not limited only to discussing and learning the principles of the assays mentioned earlier, but it also shows their practical application in a particular diagnostic process and give the guidelines on how to explain and interpret exemplary results. In parallel, the way the case study is constructed allows a tutor to lead students into discussion on clinical aspects related to HIV infection what should eventually create complete picture of a HIV diagnostic process, thereby integrating basic knowledge of molecular biology laboratory techniques, HIV biology, and immunological response. © 2019 International Union of Biochemistry and Molecular Biology, 47(3):355-360, 2019.

A retrospective analysis of the application of the Elecsys® HIV combi PT assay in southern China

BACKGROUND

Fourth-generation HIV assays have been implemented worldwide as a screening test for many years. Understanding the performance of fourth-generation assay in low HIV prevalence region is pivotal to interpret the test result correctly. In this study, retrospective analysis was used to evaluate application of the Elecsys^® HIV combi PT assay.

METHODS

A total of 85 043 specimens from a low prevalence setting were detected between June 2013 and October 2015. We evaluated the false-positive rate (FPR), specificity, and positive predictive value (PPV).

RESULTS

The specificity between male and female were 99.85% and 99.82%, respectively. The PPV on male (50.75%) was higher than female (17.05%) significantly, while the FPR was 0.15% and 0.18%. The gap between false-positive (median: 1.83, [IQR]: 1.30, 3.38) and confirmed-positive (median: 407.5, [IQR]: 184.2, 871.7) is enormous. The highest s/co ratio for false-positive cases was 85.45, while the lowest s/co ratio for confirmed-positive cases was 59.68. Various reasons were attributed to false-positive cases.

CONCLUSION

Optimal cutoff value is needed to be set to reduce the false-positive cases and predict the final status of HIV infection reliably. Retrospective analysis will help us to understand more about diagnosis of HIV.