For a patient with confirmed active pulmonary tuberculosis, what baseline screening investigations should be obtained prior to starting treatment?

Baseline Screening Tests for Active Pulmonary Tuberculosis

For a patient with confirmed active pulmonary tuberculosis, obtain the following baseline screening tests before starting treatment: sputum for smear and culture with drug susceptibility testing, chest radiograph, HIV testing, liver function tests, baseline complete blood count and creatinine, hepatitis B and C screening in at-risk patients, fasting glucose or HbA1c in those with diabetes risk factors, and baseline visual acuity testing if ethambutol will be used. 11

Essential Microbiological Testing

Sputum Studies:

• Collect sputum for acid-fast bacilli (AFB) smear and culture at baseline
• At least one baseline specimen must be tested using a rapid molecular test (e.g., GeneXpert MTB/RIF)
• Obtain drug susceptibility testing for isoniazid, rifampin, ethambutol, and pyrazinamide on all initial isolates
• Molecular resistance testing should be performed for patients with risk factors for drug resistance 11

This microbiological workup is critical because it establishes the baseline bacterial burden, confirms the diagnosis, and most importantly identifies drug resistance patterns that will determine the appropriate treatment regimen.

Imaging Studies

Chest Radiograph:

• Obtain baseline chest X-ray for all patients
• This serves as a reference point for monitoring treatment response and documents the extent of disease 11

Mandatory Screening for Comorbidities

HIV Testing:

• Universal HIV testing is required for all TB patients
• If positive, obtain CD4 lymphocyte count and HIV RNA viral load
• This is non-negotiable as HIV co-infection fundamentally alters treatment approach, prognosis, and requires coordination of antiretroviral therapy 11

Hepatitis B and C Screening:

• Screen patients with risk factors including:
  • Injection drug use
  • Birth in Asia or Africa
  • HIV infection
• This is essential because hepatitis significantly increases hepatotoxicity risk from TB medications 11

Diabetes Screening:

• Obtain fasting glucose or hemoglobin A1c for patients with risk factors:
  • Age >45 years
  • BMI >25 kg/m²
  • First-degree relative with diabetes
  • High-risk race/ethnicity (African American, Asian, Hispanic, American Indian/Alaska Native, Hawaiian Native/Pacific Islander)
• Diabetes impairs TB treatment outcomes and requires careful monitoring 11

Baseline Laboratory Monitoring

Liver Function Tests:

• Obtain baseline ALT and AST in all patients
• This is particularly important for patients who:
  • Chronically consume alcohol
  • Take other potentially hepatotoxic medications
  • Have viral hepatitis or history of liver disease
  • Are HIV-positive
• Baseline values guide decisions about treatment modifications if hepatotoxicity develops 11

Additional Baseline Labs:

• Complete blood count
• Serum creatinine
• These are needed to assess baseline organ function and adjust medication dosing 11

Medication-Specific Baseline Testing

Visual Assessment (if ethambutol planned):

• Baseline visual acuity using Snellen test
• Color discrimination testing
• These establish a baseline before starting ethambutol, which can cause optic neuritis 11

Weight Documentation

• Record baseline weight for proper medication dosing
• TB medications are weight-based, and accurate dosing is critical for treatment success 11

Critical Pitfalls to Avoid

Do not start treatment without:

• Drug susceptibility testing results pending (though treatment can begin while awaiting results)
• HIV status determination
• Baseline liver function in high-risk patients

Common mistake: Failing to screen for hepatitis B/C in at-risk populations leads to preventable severe hepatotoxicity during TB treatment.

Important caveat: While liver function tests are recommended at baseline for all patients per guidelines, they are most critical for those with risk factors. However, given the hepatotoxic nature of first-line TB drugs, obtaining baseline values in all patients provides a reference point if symptoms develop during treatment.

The 2016 ATS/CDC/IDSA guidelines 11 provide the most authoritative and comprehensive framework for baseline evaluation, emphasizing that these screening tests directly impact treatment decisions, monitoring strategies, and ultimately patient outcomes including mortality and quality of life.