What blood tests should be monitored in a patient on anti-tuberculosis (TB) medication?

Blood Monitoring for Patients on Anti-TB Therapy

Baseline liver function tests (AST, ALT, bilirubin, alkaline phosphatase), serum creatinine, complete blood count, and platelet count should be obtained in all adult patients before starting anti-TB treatment, with routine follow-up monitoring reserved only for those with baseline abnormalities or specific risk factors for hepatotoxicity. 1

Baseline Blood Tests Required

All patients starting anti-TB therapy require the following baseline assessments:

• Liver function tests: AST, ALT, bilirubin, and alkaline phosphatase 1
• Renal function: Serum creatinine 1
• Hematologic parameters: Complete blood count and platelet count 1
• HIV testing: All TB patients should be tested, with CD4 count and viral load if positive 1
• Hepatitis B and C screening: For patients with risk factors including injection drug use, birth in Asia or Africa, or HIV infection 1
• Fasting glucose or HbA1c: For patients with diabetes risk factors (age >45 years, BMI >25 kg/m², first-degree relative with diabetes, or high-risk race/ethnicity) 1

During Treatment Monitoring Strategy

Patients WITHOUT Risk Factors

Routine monthly liver function monitoring is NOT necessary during treatment if baseline tests are normal and the patient has no risk factors. 1 Instead, rely on:

• Monthly clinical assessments to identify symptoms of hepatotoxicity (jaundice, dark urine, nausea, vomiting, abdominal pain, fever, malaise) 1
• Symptom-triggered testing: Obtain liver function tests immediately if any hepatotoxicity symptoms develop 1

Patients WITH Risk Factors Requiring Regular Monitoring

Obtain liver function tests at baseline and regularly during treatment for patients with: 1

• Baseline liver function abnormalities
• Chronic alcohol consumption
• Viral hepatitis (B or C)
• HIV infection
• History of liver disease
• Concurrent use of other hepatotoxic medications

For high-risk patients, one study suggests monitoring twice weekly for the first 2 weeks, every 2 weeks during months 1-2, then monthly thereafter, 2 though the most recent ATS/CDC/IDSA guidelines emphasize clinical monitoring over routine biochemical testing 1

Ethambutol-Specific Monitoring

For patients receiving ethambutol: 1

• Baseline: Visual acuity (Snellen test) and color discrimination testing
• Monthly: Inquiry about visual disturbances and color discrimination testing
• Immediate evaluation: If any visual symptoms develop (blurred vision, scotomata)

Critical Thresholds for Action

Stop all hepatotoxic TB drugs (isoniazid, rifampin, pyrazinamide) immediately if: 3

• Liver enzymes rise to ≥5 times upper limit of normal WITHOUT symptoms, OR
• Liver enzymes rise to ≥3 times upper limit of normal WITH hepatitis symptoms (nausea, vomiting, jaundice, abdominal pain)

Continue treatment with non-hepatotoxic drugs (ethambutol plus fluoroquinolone or injectable agent) if the patient remains infectious or acutely ill 3

Additional Monitoring Parameters

• Monthly sputum smear and culture until 2 consecutive specimens are negative 1
• Monthly weight assessment to adjust medication doses as needed 1
• Monthly adherence assessment and symptom review 1

Common Pitfalls to Avoid

Do not over-monitor low-risk patients. The 2016 ATS/CDC/IDSA guidelines explicitly state that routine liver function monitoring is unnecessary in patients without baseline abnormalities or risk factors, as this approach has not been shown to prevent severe hepatotoxicity and may lead to unnecessary treatment interruptions 1

Do not ignore clinical symptoms. Even with normal baseline tests, patients must be educated to report hepatotoxicity symptoms immediately, as symptomatic hepatotoxicity can develop rapidly 3, 2

Do not continue hepatotoxic drugs when thresholds are exceeded. Recent evidence shows that scheduled monitoring in high-risk patients facilitates earlier detection of hepatotoxicity (14.7 vs 61.6 days) and results in lower peak ALT levels (276 vs 507 IU/L), reducing severity of liver injury 4

Monitor more frequently in special populations. Patients with extrapulmonary TB, comorbid diseases, and advanced age have significantly higher rates of drug-induced hepatotoxicity (7.9% incidence overall, higher in these subgroups) and warrant closer biochemical surveillance 5