What lab work should be checked before starting a patient on a Glucagon-like peptide-1 (GLP-1) receptor agonist, such as liraglutide (Victoza) or semaglutide (Ozempic), particularly in those with a history of thyroid cancer or multiple endocrine neoplasia type 2 (MEN2)?

Pre-Initiation Laboratory Work for GLP-1 Receptor Agonists

Check baseline HbA1c, comprehensive metabolic panel (including renal function/eGFR), and lipid panel before starting any GLP-1 receptor agonist. 1

Essential Laboratory Tests

Mandatory Baseline Labs

• HbA1c and fasting glucose to establish baseline glycemic control and assess treatment response at follow-up 1
• Comprehensive metabolic panel (CMP) including serum creatinine and eGFR to assess kidney function, as GLP-1 RAs have renal effects and some agents require dose adjustments 1
• Liver enzymes (ALT, AST) to establish baseline hepatic function, particularly important given potential benefits in NAFLD/NASH 1
• Lipid panel (total cholesterol, LDL, HDL, triglycerides) to assess baseline cardiovascular risk and monitor improvement 1

Additional Screening Based on Clinical Context

• Thyroid function tests are NOT routinely required before initiating GLP-1 RAs, but document any personal or family history of medullary thyroid cancer or MEN2, which are absolute contraindications 1, 2
• Calcitonin levels are NOT recommended as routine screening before GLP-1 RA initiation, despite the theoretical thyroid C-cell tumor risk seen in rodent studies 1, 2
• Amylase/lipase are NOT required at baseline unless the patient has a history of pancreatitis, in which case use liraglutide or semaglutide with caution 1, 2

Critical Contraindications to Screen For (History, Not Labs)

Absolute contraindications that require screening through history, not laboratory work: 1, 2

• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple endocrine neoplasia syndrome type 2 (MEN2)
• History of serious hypersensitivity reaction to the specific GLP-1 RA

Renal Function Considerations

Agent-Specific Renal Thresholds

• Liraglutide, dulaglutide, and semaglutide require no dose adjustment across all stages of CKD, including eGFR <30 mL/min/1.73 m² or end-stage renal disease 2
• Exenatide is contraindicated when eGFR <30 mL/min/1.73 m² and should not be used in end-stage renal disease or patients on dialysis 2
• Lixisenatide is contraindicated when eGFR <30 mL/min/1.73 m² 2

Why Renal Function Matters

• GLP-1 RAs reduce albuminuria and slow eGFR decline, making baseline measurement essential for monitoring renal protective effects 3, 4, 5
• The MACE risk reduction with liraglutide is significantly greater for those with eGFR <60 ml/min/1.73 m² than for those with eGFR ≥60 ml/min/1.73 m² 3

Pre-Treatment Clinical Assessments (Not Labs)

Ophthalmologic Evaluation

• Comprehensive dilated eye examination is recommended if not done within the last 12 months before starting therapy, particularly for semaglutide due to increased diabetic retinopathy complications 1
• This is especially critical for patients with proliferative retinopathy, where semaglutide should be used with caution 1

Medication Review

• Discontinue DPP-4 inhibitors before starting GLP-1 RAs, as concurrent use provides no additional benefit 1
• Reduce sulfonylurea dose by 50% or basal insulin dose by 20% if HbA1c is well-controlled at baseline to prevent hypoglycemia 1

Common Pitfalls to Avoid

• Do not order calcitonin levels routinely as screening for medullary thyroid cancer—this is not recommended and creates unnecessary anxiety 1, 2
• Do not delay treatment waiting for specialized thyroid imaging or endocrinology consultation unless there is a documented personal or family history of MTC or MEN2 1, 2
• Do not assume all GLP-1 RAs are contraindicated in severe CKD—liraglutide, dulaglutide, and semaglutide can be safely used even with eGFR <30 mL/min/1.73 m² 2
• Do not forget to check baseline weight and blood pressure, as these are critical monitoring parameters but are clinical measurements, not laboratory tests 1

Monitoring Schedule After Initiation

• Recheck HbA1c at 3 months to assess glycemic response 1
• Monitor renal function (eGFR) when initiating or escalating doses, particularly with semaglutide and dulaglutide 2
• Assess weight, blood pressure, and cardiovascular risk factors at least every 3 months after reaching maintenance dose 1