Drug Susceptibility Testing (DST)

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Brief Description

Drug Susceptibility Testing (DST) determines the ability of the four primary antitubercular drugs to inhibit the growth (in vitro) of Mycobacterium tuberculosis complex (MTBC) in a broth macrodilution matrix which utilizes critical concentrations of drugs tested. DST is important to the proper treatment and management of patients with tuberculosis (TB).  DST guides the physician in the selection of the most appropriate drug treatment regimen and alerts the physician when drug resistance may be a consideration in patient management.

Laboratory Unit



Broth macrodilution using BACTEC MGIT system

Specimen Collection

Viable isolate of M. tuberculosis complex in pure culture of solid or liquid media


Submit isolates using the TB Category A carrier provided by the MSPHL in accordance with the Infectious Substance, Category A shipping guidelines.

Acceptable Specimen

Pure culture of M. tuberculosis complex.

Test Request Form(s)

Tuberculosis Test Request Form

Possible Results


Reference Range

Isoniazid (0.1 & 0.4 mcg/mL)
Rifampin (1.0 mcg/mL)
Ethambutol (5.0 mcg/mL)
Pyrazinamide (100 mcg/mL)

Unacceptable Conditions

Leaked during transport
No name on specimen
Mixed culture
Nonviable organism

Interfering Substances


Result Reported

4 – 28 days after receipt of specimen



CPT Codes

87188 x5



Additional Information

M. tuberculosis complex showing resistances to any drug are referred to the Centers for Disease Control and Prevention (CDC) for secondary drug susceptibility testing.

19 CSR 20-20.080 Duties of Laboratories

"Isolates or specimens positive for [M. tuberculosis complex] must be submitted to the State Public Health Laboratory for epidemiological or confirmation purposes"