What baseline laboratory tests should be obtained before initiating tirzepatide (Mounjaro)?

Baseline Laboratory Tests Before Starting Mounjaro (Tirzepatide)

Obtain fasting glucose or HbA1c, a comprehensive metabolic panel including liver function tests, lipid profile, pregnancy test (if applicable), and calculate FIB-4 index to screen for liver fibrosis—routine baseline liver enzymes are not mandatory but should be obtained in patients with obesity-related metabolic risk factors. 1

Required Baseline Laboratory Tests

Glycemic Assessment

• Fasting blood glucose or HbA1c to establish baseline glycemic status and assess diabetes risk 1
• This is essential even if you're prescribing tirzepatide primarily for weight loss rather than diabetes management

Metabolic Panel

• Comprehensive metabolic panel (CMP) including:
  • Liver function tests (ALT, AST) 1
  • Renal function (creatinine, BUN) 1
  • Electrolytes 1

Lipid Profile

• Fasting lipid panel to establish baseline values, as GLP-1/GIP receptor agonists affect lipid metabolism 1

Liver Fibrosis Screening

• Calculate FIB-4 index using age, ALT, AST, and platelet count to screen for clinically significant liver fibrosis 2
• This is recommended for all adults with obesity and metabolic risk factors, even when liver enzymes are normal 2
• The FIB-4 calculation requires: age, ALT, AST, and platelet count—all obtainable from the CMP and CBC

Pregnancy Testing

• Pregnancy test for all women of childbearing potential before initiating therapy 1
• Tirzepatide delays gastric emptying, which can reduce absorption of oral contraceptives 3

Additional Baseline Assessments (Non-Laboratory)

Anthropometric Measurements

• Body mass index (BMI) and waist circumference should be documented at baseline 1
• These serve as reference points for monitoring weight loss efficacy

Critical History Screening

• Screen for personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (MEN 2)—these are absolute contraindications due to the black box warning 3, 1
• Evaluate history of pancreatitis, as GLP-1/GIP receptor agonists may increase pancreatitis risk 3, 1

When Baseline Liver Enzymes Are Specifically Indicated

While a CMP with liver function tests is recommended for all patients, baseline ALT/AST measurement is particularly important in:

• Patients with significant alcohol consumption (>20 g/day for women or >30 g/day for men) 2
• Known or suspected non-alcoholic fatty liver disease (NAFLD/NASH), which is common in obesity 2
• History of chronic liver disease (hepatitis B or C, cirrhosis) 4
• Regular use of other hepatotoxic medications 4

What You Do NOT Need at Baseline

• Routine bilirubin is not required unless the FIB-4 index suggests advanced fibrosis or liver enzymes are elevated 2
• Thyroid function tests are not required before starting tirzepatide (unlike some other medications)
• Lipase or amylase are not routinely indicated unless there is clinical suspicion of pancreatitis
• Cardiac biomarkers are not required, though blood pressure should be documented 1

Monitoring Schedule After Initiation

First 3 Months

• Monthly assessment of BMI, blood pressure, and adverse effects 1
• Monthly evaluation during dose escalation phase to assess tolerability 3

After 3 Months

• Quarterly BMI measurement 1
• Reassess blood pressure, fasting glucose, and lipids at 3 months, then yearly thereafter 1
• Evaluate treatment efficacy at 12-16 weeks on the maximum tolerated dose 3

Common Pitfalls to Avoid

• Do not skip the FIB-4 calculation—many patients with obesity have undiagnosed NAFLD/NASH, and tirzepatide can improve liver health, but you need a baseline 2
• Do not forget pregnancy testing—tirzepatide affects oral contraceptive absorption, and patients need counseling about adding non-oral contraception for 4 weeks after initiation and each dose escalation 3
• Do not order routine thyroid function tests unless clinically indicated—the black box warning is about medullary thyroid carcinoma (screened by history), not thyroid dysfunction
• Do not assess treatment response at 1 month—the 2.5 mg starting dose is for tolerability, not efficacy; evaluate at 12-16 weeks on therapeutic doses (5 mg, 10 mg, or 15 mg) 2