What baseline investigations, including visual acuity, liver function tests (LFTs) such as alanine transaminase (ALT) and aspartate transaminase (AST), and renal function tests (RFTs) such as creatinine, are cost-effective for patients starting tuberculosis (TB) treatment with medications like ethambutol, isoniazid, and pyrazinamide?

Cost-Effective Baseline Investigations for TB Medications

Baseline investigations for TB medications should be targeted based on specific medication risks and patient factors, with visual acuity testing required only for patients on ethambutol, and liver function tests recommended for all patients but with routine monitoring only for those with risk factors. 1

Essential Baseline Investigations

For All Patients Starting TB Treatment:

• Sputum smear and culture with drug susceptibility testing 1
• Chest radiograph 1
• HIV testing 1
• Baseline weight (for medication dosing) 1
• Serum creatinine and estimated GFR 1
• Liver function tests (AST, ALT, bilirubin) 1

Medication-Specific Baseline Tests:

• For ethambutol: Visual acuity (Snellen test) and color discrimination tests 1, 2
• For patients with hepatitis risk factors: Hepatitis B and C screening 1
• For patients with diabetes risk factors: Fasting glucose or HbA1c 1

Cost-Effective Monitoring Approach

Visual Acuity Testing:

• Only required at baseline for patients receiving ethambutol 1
• Monthly follow-up with color discrimination tests for patients on ethambutol 1, 2
• Not necessary for patients not receiving ethambutol

Liver Function Tests (LFTs):

• Baseline LFTs for all patients 1
• Routine follow-up LFTs only needed for patients with:
  • Abnormal baseline LFTs
  • Symptoms of hepatotoxicity
  • Chronic alcohol consumption
  • Concurrent hepatotoxic medications
  • Viral hepatitis or history of liver disease
  • HIV infection 1

Renal Function Tests:

• Baseline creatinine for all patients 1
• Further monitoring only if baseline abnormalities or clinically indicated 1

Risk-Based Monitoring Strategy

High-Risk Patients Requiring More Intensive Monitoring:

• Patients with pre-existing liver disease: Weekly LFTs for first 2 weeks, then every 2 weeks for first 2 months 1
• Elderly patients (>65 years): Consider more frequent LFT monitoring 1
• HIV co-infected patients: More frequent monitoring of all parameters 1
• Patients with chronic liver disease: Consider monthly LFT monitoring 3

Monitoring Thresholds for Action:

• Stop hepatotoxic drugs (isoniazid, rifampin, pyrazinamide) if:
  • AST/ALT rises to 3× upper limit of normal with symptoms
  • AST/ALT rises to 5× upper limit of normal without symptoms 1, 3
• For ethambutol: Discontinue if any decrease in visual acuity occurs that cannot be attributed to other causes 2

Practical Implementation

• Educate patients about potential side effects and when to seek medical attention 1
• Schedule clinical evaluations at least monthly to assess for medication side effects 1
• Use symptom-based monitoring between visits (patients should report visual changes, jaundice, nausea, abdominal pain, etc.) 1, 2
• Consider fixed-dose combinations to improve adherence and potentially reduce costs 1

This targeted approach to baseline and follow-up testing balances the need for safety monitoring with cost-effectiveness by focusing intensive monitoring on high-risk patients while using a more streamlined approach for low-risk individuals.