The normal reference value for Mycobacterium tuberculosis nucleic acid assay is negative. Mycobacterium tuberculosis nucleic acid assay (TB DNA), that is, the application of polymerase chain reaction (PCR) technology to detect Mycobacterium tuberculosis, compared with the traditional antacid bacillus smear staining and microscopic examination, it can significantly improve the detection rate and specificity of Mycobacterium tuberculosis, and is conducive to the timely diagnosis of tuberculosis in the clinic and treatment of tuberculosis to provide the basis for the test reference value of the negative, positive can be seen in a variety of tuberculosis diseases. It can be used for the qualitative detection of Mycobacterium tuberculosis nucleic acid in sputum specimens of patients with suspected tuberculosis after treatment, and can also be used for the auxiliary diagnosis of tuberculosis, but sputum specimens are complicated in composition, and certain interfering substances may affect the test results.