The GLP-1 Lab Tests Your Doctor Should Be Running (But Probably Isn't)

Most GLP-1 Prescriptions Come with Minimal Monitoring

A significant gap exists between what clinical guidelines recommend for GLP-1 patients and what happens in typical telehealth visits. Many patients receive a prescription based on BMI and a brief health questionnaire, with follow-up limited to weight checks and side-effect assessments. For short-term use, this may be adequate. For the long-term treatment that GLP-1 therapy increasingly represents, it is not enough.

The ADA 2026 guidelines and emerging clinical evidence point to a more comprehensive monitoring approach. Here are the lab tests and assessments your prescriber should be considering.

Baseline Labs (Before or Early in Treatment)

Comprehensive Metabolic Panel (CMP)

This standard blood draw covers liver function (ALT, AST), kidney function (creatinine, BUN, eGFR), blood glucose, and electrolytes. It establishes baseline values before GLP-1 therapy begins and can identify contraindications. GLP-1s are generally safe in mild kidney impairment but require dose adjustment or avoidance in severe cases.

Hemoglobin A1C

Even for patients without diabetes, A1C provides a three-month average blood sugar picture. Many patients starting GLP-1s for weight loss have undiagnosed prediabetes. Knowing your baseline A1C helps your doctor track metabolic improvement beyond weight change.

Lipid Panel

Total cholesterol, LDL, HDL, and triglycerides. GLP-1 medications often improve lipid profiles significantly — but you need a starting point to measure that improvement. Some clinicians now include Lp(a), a genetic cardiovascular risk marker, based on 2026 research showing GLP-1 users with elevated Lp(a) may get outsized cardiovascular benefit.

Thyroid Function (TSH, Free T4)

GLP-1 receptor agonists carry a boxed warning about thyroid C-cell tumors based on animal studies. While this has not been confirmed in humans, baseline thyroid testing is prudent, and patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 should not use GLP-1 medications.

Ongoing Monitoring (Every 3-6 Months)

Kidney Function (eGFR and UACR)

The ADA's 2026 Standards of Care revision specifically calls for routine kidney monitoring in patients on GLP-1 therapy. Estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR) should be checked regularly — not because GLP-1s harm the kidneys (they appear protective), but to track kidney health over time and catch any unrelated decline early.

CRP (C-Reactive Protein)

This inflammatory marker has emerged as a useful surrogate for the cardiovascular protective effects of GLP-1 therapy. Declining CRP suggests reduced systemic inflammation — one of the mechanisms by which GLP-1s protect the heart. If your CRP remains elevated despite treatment, your doctor may consider additional interventions.

Vitamin B12

Long-term GLP-1 use may affect B12 absorption, particularly with oral formulations that alter gastric pH and emptying. Symptoms of B12 deficiency (fatigue, tingling, cognitive changes) can be subtle and easily attributed to other causes. Annual monitoring is recommended for patients on long-term therapy.

Vitamin D, Iron, Folate, Calcium

Extended caloric restriction — even medically supervised — can deplete these nutrients. Patients who have significantly reduced their food intake should have these checked periodically, particularly postmenopausal women (calcium, vitamin D) and women of reproductive age (iron, folate).

Body Composition Assessment

Scale weight alone does not distinguish between fat loss and lean mass loss. Your doctor has several options for tracking body composition:

• DEXA scan: The gold standard. Measures fat, lean tissue, and bone density with high accuracy. Typically done annually.
• Bioelectrical impedance: Less accurate than DEXA but widely available and inexpensive. Many smart scales use this technology. Good for tracking trends over time.
• Waist circumference: Simple, free, and clinically meaningful. Visceral fat (measured indirectly by waist circumference) is the fat most strongly linked to cardiovascular and metabolic risk.
• Grip strength: A surprisingly good proxy for overall muscle function. Easy to measure in a clinical setting. Declining grip strength on GLP-1 therapy should prompt closer attention to protein intake and resistance training.