Abstract:

Objective To evaluate the detection efficiency of Mycobacterium tuberculosis complex by liquid-based interlayer (using the method of collecting bacteria, referred to as “smear method”), L-J solid culture method (referred to as “L-J culture method”) and nucleic acid detection of Mycobacterium tuberculosis complex group (using constant temperature amplification method; referred to as “thermostatic amplification method”). +++ Methods--- Three hospitals were randomly selected as research sites from the 120 tuberculosis designated hospitals using random number table, including Liuyang People’s Hospital, Liling Xiangdong Hospital, and Taojiang County People’s Hospital. A total of 628 patients with suspected tuberculosis symptoms diagnosed in 3 hospitals from November 1 to December 31, 2018 were included as the research subjects. The same sputum specimens were tested by smear method, L-J culture method, and thermostatic amplification method, and then the difference of positive detection rate of Mycobacterium tuberculosis complex by 3 testing methods was analyzed. In addition, according to the diagnostic criteria of 《WS 288-2017 Pulmonary Tuberculosis Diagnosis》, the clinical diagnosis of tuberculosis was used as the reference standard, and the sensitivity, specificity, positive predictive value, negative predictive value and consistency of the 3 testing methods were calculated. Based on the actual expenditure of each test performed by the patient, the testing cost of each method was calculated. Comparison of detection rate of Mycobacterium tuberculosis complex among three methods was used by Chi square test, test level α=0.05/3=0.017. Results Among 628 patients with suspected pulmonary tuberculosis, there were 153 (24.4%) patients clinically diagnosed with pulmonary tuberculosis and 6 (1.0%) patients with non-tuberculous mycobacterium pulmonary disease. The results of 3 testing methods showed that the positive detection rates of Mycobacterium tuberculosis complex by smear method, L-J culture method, and thermostatic amplification method (excluding 6 patients with non-tuberculous mycobacterium pulmonary disease) were 13.5% (84/622), 14.0% (87/622), and 12.2% (76/622), respectively. The difference of positive rate of Mycobacterium tuberculosis complex among the three test methods was not statistically significant (smear method vs. L-J culture method: χ ²=1.32, P=0.359; L-J culture method vs. thermostatic amplification method: χ ²=5.83, P=0.024; smear method vs. thermostatic amplification method: χ ²=4.00, P=0.077). Based on the clinical diagnosis as the reference standard, for smear method, L-J culture method, and thermostatic amplification method (excluding 6 patients with non-tuberculous mycobacterium pulmonary disease and 32 patients with contaminated culture), the sensitivity was 55.2% (80/145), 57.9% (84/145) and 50.3% (73/145), respectively; the specificity was 99.6% (443/445), 99.3% (442/445) and 99.8% (444/445), respectively; the positive predictive value was 97.6% (80/82), 96.6% (84/87) and 98.6% (73/74), respectively; the negative predictive value was 87.2% (443/508), 87.9% (442/503) and 86.0% (444/516), respectively; and the coincidence rate was 88.6% (523/590), 89.2% (526/590) and 87.6% (517/590), respectively. The cost of three methods was calculated from low to high in order: L-J culture method: 317.2 yuan (29 500/93), smear method: 813.8 yuan (70800/87), and thermostatic amplification method: 1992.2 yuan (153400/77). Conclusion There is no difference among the three detection methods in terms of positive detection rate, sensitivity and specificity. When a patient with positive etiology is found, L-J culture method has the lowest cost, while thermostatic amplification method has the highest cost.

Key words: Mycobacterium tuberculosis, Clinical laboratory techniques, Colony count,microbial, Culture techniques, Nucleic acid amplification techniques, Cost-benefit analysis, Comparative study