It depends on whether there is other etiological evidence.
According to the latest version of Guidelines on Diagnosis and Treatment of COVID-19 (trial edition 6), a confirmed diagnosis of COVID-19 requires positive etiological evidence (real-time fluorescent RT-PCR shows positive result of nucleic acid test for 2019-nCov, or viral gene sequencing is highly homologous to the known 2019-nCov).
If a patient has negative nucleic acid test, but his blood test for virus gene (that is, virus gene sequencing) is positive, then he can also be diagnosed.
However, if a patient has negative nucleic acid test without receiving virus gene test, he cannot be diagnosed as COVID-19 only based on chest CT scans or other tests. The main reason is that the low specificity of CT scam may misdiagnosed other lung diseases as COVID-19.