Antikörpertests bei COVID-19 - Was uns die Ergebnisse sagen

Horvath, Karl; Semlitsch, Thomas; Jeitler, Klaus; Krause, Robert; Siebenhofer, Andrea

INTRODUCTION: In the context of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, the detection of virus-specific antibodies (AB) will play an increasing role. The presence or absence of such antibodies can potentially lead to considerations regarding immunity and infection. ISSUE: How reliable are inferences from positive or negative test results regarding the actual presence of SARS-CoV-2 specific antibodies? METHODS: Calculation of the probability that, depending on the pretest probability (prevalence of SARS-CoV-2 infection) and test properties, antibodies are present or absent in the case of positive or negative test results. RESULTS: Sensitivity and specificity of different SARS-CoV-2 AB test systems vary between 53 % and 94 % and between 91 % and 99.5 %, respectively. When using a test with high test quality, the positive predictive value (PPV) is 42 % and 7 9%, respectively, with a pre-test probability of 1 % to 5 %, as can currently be assumed for the general population in Austria or Germany. For persons with an increased pre-test probability of 20 %, e. g. persons from high-risk professions, the PPW is 95 %, with a pre-test probability of 80 % the PPW is almost 100 %. The negative predictive value (NPV) is at least 99.7 % for persons with a low pre-test probability of up to 5 % and 79.1 % for persons with a pre-test probability of 80 %. When using test systems with lower sensitivity and specificity, the reliability of the results decreases considerably. The PPV is 5.9 % with a pre-test probability of 1 %. CONCLUSIONS: A sufficiently high sensitivity and specificity are prerequisites for the application of antibody test systems. Positive test results are often false if the pre-test probability is low. Depending on the assumed prevalence of a SARS-CoV-2 infection, there are substantial differences in the significance of a concrete test result for the respective affected persons.