LAUSR

To the Editor, Since the emergence of SARS‐CoV‐2, many diagnostic tests including molecular and serological assays have been developed and approved by the Food and Drug Administration (FDA) for diagnosis of COVID‐19. However, concerns about the sensitivity and specificity of many diagnostic assays, especially the rapid tests, have been raised. Diagnostic tests with unacceptable rates of false positive and false‐negative results interfere with therapeutic management of patients and can have serious implications for public health authorities in the decision‐making process regarding COVID‐19 control. In this context, understanding key concepts in terms of development and validation of diagnostic assays is crucial for correct interpretation of test results. The parameters for validating diagnostic tests include analytical sensitivity, analytical specificity, clinical sensitivity, clinical specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value (PPV), negative predictive value (NPV), repeatability, reproducibility, and accuracy (Table 1). After initial development and optimization of a new COVID‐19 test, the performance of the assay should be assessed using a set of well‐ defined clinical samples taking into account the required sample size. Ideally, data used for validation of the COVID‐19 test should be published in a peer‐reviewed publication to allow independent evaluation. Validation is essential for the development of a diagnostic test and requires a series of interrelated steps where the diagnostic test is experimentally standardized to detect the analyte (antibody, antigen, nucleic acid [DNA or RNA]), with precision and high accuracy. Importantly, the new test should be compared side‐by‐side to a gold standard method that is used as a reference method to detect the pathogen. In the case of SARS‐CoV‐2, quantitative reverse transcription polymer chain reaction (RT‐qPCR) is considered the reference test for the laboratory diagnosis of COVID‐19 patients recommended by the World Health Organization (WHO). Recently, several studies have raised concerns about false‐ negative RT‐qPCR results in patients with COVID‐19 disease during the pandemic course. In a recent study, Li et al. tested specimens collected from 610 hospitalized patients from Wuhan, China, and found a high rate of false‐negative RT‐qPCR results. There are a number of reasons that may produce false‐negative results, including low viral load in the patient sample, inadequate storage during specimen transportation, laboratory error during sampling, low sensitivity of the diagnostic test, or the use of the unsuitable diagnostic mode according to date of sample collection post the onset of