How to use imperfect tests for COVID-19 (SARS-CoV-2) to make clinical decisions

COVID-19 rapid antigen tests approved for self-testing in Australia: published diagnostic test accuracy studies and manufacturer-supplied information. A systematic review

OBJECTIVES

To review evaluations of the diagnostic accuracy of coronavirus disease 2019 (COVID-19) rapid antigen tests (RATs) approved by the Therapeutic Goods Administration (TGA) for self-testing by ambulatory people in Australia; to compare these estimates with values reported by test manufacturers.

STUDY DESIGN

Systematic review of publications in any language that reported cross-sectional, case-control, or cohort studies in which the participants were ambulatory people in the community or health care workers in hospitals in whom severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was suspected, and the results of testing self-collected biological samples with a TGA-approved COVID-19 RAT were compared with those of reverse transcription-polymerase chain reaction (RT-PCR) testing for SARS-CoV-2. Estimates of diagnostic accuracy (sensitivity, specificity) were checked and compared with manufacturer estimates published on the TGA website.

DATA SOURCES

Publications (to 1 September 2022) identified in the Cochrane COVID-19 Study Register and the World Health Organization COVID-19 research database. Information on manufacturer diagnostic accuracy evaluations was obtained from the TGA website.

DATA SYNTHESIS

Twelve publications that reported a total of eighteen evaluations of eight RATs approved by the TGA for self-testing (manufacturers: All Test, Roche, Flowflex, MP Biomedicals, Clungene, Panbio, V-Chek, Whistling) were identified. Five studies were undertaken in the Netherlands, two each in Germany and the United States, and one each in Denmark, Belgium, and Canada; test sample collection was unsupervised in twelve studies, and supervised by health care workers or researchers in six. Estimated sensitivity with unsupervised sample collection ranged from 20.9% (MP Biomedicals) to 74.3% (Roche), and with supervised collection from 7.7% (V-Chek) to 84.4% (Panbio); the estimates were between 8.2 and 88 percentage points lower than the values reported by the manufacturers. Test specificity was high for all RATs (97.9-100%).

CONCLUSIONS

The risk of false negative results when using COVID-19 RATs for self-testing may be considerably higher than apparent in manufacturer reports on the TGA website, with implications for the reliability of these tests for ruling out infection.

Derivation of a HEAR Pathway for Emergency Department Chest Pain Patients to Safely Avoid a Second Troponin Test

The study aims to develop a decision pathway based on HEAR score and 0 h high-sensitivity cardiac troponin T (hs-cTnT) to safely avoid a second troponin test for suspected non-ST elevation myocardial infarction (NSTEMI) in emergency departments. A HEAR score consists of history, electrocardiogram, age, and risk factors. A HEAR pathway is established using a Bayesian approach based on a predefined safety threshold of NSTEMI prevalence in the rule-out group. In total, 7131 patients were retrospectively enrolled, 582 (8.2%) with index visit NSTEMI and 940 (13.2%) with 180-day major adverse cardiovascular events (MACE). For patients with a low-risk HEAR score (0 to 2) and low 0 h hs-cTnT (<14 ng/L), the HEAR pathway recommends early discharge without further testing. After the HEAR pathway had been applied to rule out NSTEMI, the negative predictive value of index visit NSTEMI was 100.0% (95% CI, 99.8% to 100.0%) and false-negative rate of 180-day MACE was 0.40% (95% CI, 0.18% to 0.87%). Compared with the 0 h hs-cTnT < limit of detection (LoD) strategy (<5 ng/L), the HEAR pathway could correctly reclassify 1298 patients without MACE as low risk and lead to a 18.2% decrease (95% CI, 17.4-19.1%) in the need for a second troponin test. The HEAR pathway may lead to a substantial and safe reduction in repeated troponin test for emergency department patients with suspected NSTEMI.

Setting minimum clinical performance specifications for tests based on disease prevalence and minimum acceptable positive and negative predictive values: Practical considerations applied to COVID-19 testing

OBJECTIVES

Several guidelines for the evaluation of laboratory tests for severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection have recommended establishing an a priori definition of minimum clinical performance specifications before test selection and method evaluation.

METHODS

Using positive (PPV) and negative predictive values (NPV), we constructed a spreadsheet tool for determining the minimum clinical specificity (conditional on NPV or PPV, sensitivity and prevalence) and minimum clinical sensitivity (conditional on NPV or PPV, specificity and prevalence) of tests.

RESULTS

At a prevalence of 1%, there are no minimum sensitivity requirements to achieve a desired NPV of 60%-95% for a given clinical specificity above 20%. It is not possible to achieve 60-95% PPV even with 100% clinical sensitivity, except when the clinical specificity is near 100%. The opposite trend is seen in high prevalence settings (60%), where a relatively low minimum clinical sensitivity is required to achieve a desired PPV for a given clinical specificity, and a higher minimum clinical specificity is required to achieve a desired NPV for a given clinical sensitivity.

DISCUSSION

The selection of laboratory tests and the testing strategy for SARS-CoV-2 involves delicate trade-offs between NPV and PPV based on prevalence and clinical sensitivity and clinical specificity. Practitioners and health authorities should carefully consider the clinical scenarios under which the test result will be used and select the most appropriate testing strategy that fulfils the a priori defined clinical performance specification.