A negative reaction/result in a test, indicating that the tested substance or condition was not detected.
コロナ検査の結果は陰性反応だったので、自宅待機を続けた。
The COVID test result was negative, so they continued to stay at home.
血液検査で陰性反応が出た場合は追加検査を勧められることがある。
If a blood test shows a negative result, additional tests may be recommended.