ABSTRACT
OBJECTIVES: We conducted a nationwide external quality assessment (EQA) study of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid amplification testing in Japan. METHODS: A total of 563 public health and private sector laboratories participated. The EQA samples comprised 6 RNA and full-process controls. RESULTS: The overall agreements were 99.3% and 97.9% for the RNA and full-process controls, respectively. A total of 530/563 (94.1%) laboratories reported correct results; public health laboratories had the highest accuracy. Thirty-three laboratories reported at least one incorrect result (26 laboratories of medical facilities, 5 commercial laboratories, 1 public health laboratory, and 1 other). Sixteen laboratories of medical facilities that used a fully automated assay system failed to detect the presence of the full-process control, due to inherent insufficiency in the limit of detection (LOD). Other causes of incorrect results included failure to ensure the LOD (n = 13), error in result judging or reporting (n = 3), and error in sample handling (n = 1). CONCLUSIONS: Performance was mostly dependent on the laboratory category and assay evaluation, particularly the LOD. Guidance should be developed based on these results, particularly in the phase of new entry into laboratory services for SARS-CoV-2.