What to test before starting GLP-1 therapy: the complete pre-treatment panel

Both semaglutide and tirzepatide carry a black-box warning for medullary thyroid carcinoma risk. Personal or family history of MTC or multiple endocrine neoplasia type 2 is a contraindication. Beyond the contraindication, undetected hypothyroidism causes treatment-resistant weight loss — subclinical hypothyroidism (TSH 2.5–4.5 with normal T4) is common and frequently undertreated.

HbA1c above 6.5% indicates T2D — this changes prescribing context, monitoring frequency, and the choice between Wegovy vs Zepbound. HbA1c 5.7–6.4% indicates pre-diabetes, which significantly increases the clinical case for GLP-1 therapy and informs response prediction. Without this baseline, you cannot measure glycemic improvement over time.

HOMA-IR = (fasting insulin × fasting glucose) ÷ 405. This calculation requires both values drawn fasting. HOMA-IR above 2.5 indicates significant insulin resistance and predicts faster initial weight loss response to GLP-1 therapy. It also identifies patients who need more aggressive protein and exercise protocols to prevent lean mass loss.

Metabolic-associated fatty liver disease (MAFLD) is present in 40–70% of GLP-1 candidate patients. Baseline liver enzymes establish whether hepatic steatosis is present — GLP-1 therapy significantly improves MAFLD, and the baseline allows you to measure this benefit. Elevated enzymes above 3x the upper limit of normal warrant investigation before starting therapy.

Kidney function determines dosing safety. eGFR below 30 mL/min/1.73m² requires dose adjustment for most GLP-1 agonists. eGFR below 15 is a relative contraindication. Kidney function should be rechecked at each dose escalation step. Patients with chronic kidney disease benefit significantly from GLP-1 therapy but need closer monitoring.

Obesity reduces SHBG, which affects free testosterone calculation. Low testosterone dramatically increases lean mass loss during caloric restriction. GLP-1 therapy at 6 months has documented testosterone increases of 10–15% in men — knowing the baseline is required to measure this benefit and to decide whether concurrent peptide therapy (CJC-1295/Ipamorelin) is appropriate.

Elevated cortisol (above 20 μg/dL drawn AM) drives visceral fat accumulation that is more resistant to GLP-1 therapy. High cortisol also increases lean mass loss risk. GLP-1 therapy affects the HPA axis; establishing the baseline allows correct attribution of any cortisol changes during treatment.

hsCRP above 3.0 mg/L indicates high cardiovascular risk and systemic inflammation. GLP-1 therapy reduces hsCRP by approximately 40% at 12 months — a significant benefit that is only measurable against a baseline. Elevated homocysteine (above 15 μmol/L) indicates B12/folate deficiency and cardiovascular risk, and informs supplementation choices.

Triglycerides above 400 mg/dL make LDL cholesterol calculation unreliable — LDL-P (particle count) is more accurate in this range. HDL below 40 mg/dL combined with elevated triglycerides is the lipid pattern most responsive to tirzepatide's GIP action, informing medication choice. GLP-1 therapy significantly improves lipid profiles — the baseline makes this measurable.

Vitamin D deficiency (present in approximately 40% of adults with obesity) reduces insulin sensitivity — directly counterproductive during GLP-1 therapy. B12 deficiency worsens the nausea and fatigue that GLP-1 therapy itself causes. Both are inexpensive to correct and meaningfully improve the early therapy experience when addressed before starting.

What to do if labs are abnormal

Elevated TSH above 10 mIU/L: discuss with an endocrinologist before starting GLP-1. Liver enzymes above 3x the upper limit of normal: investigate the cause before initiating therapy. Low eGFR: dose protocols require adjustment and closer monitoring cadence. In all cases, the prescribing physician reviews results and determines whether to proceed, modify, or delay the protocol. Abnormal labs are not automatic disqualifiers — they are information that informs the approach.

The WellSpry baseline panel

WellSpry's pre-GLP-1 panel covers all 10 biomarker categories above — plus 62 additional biomarkers that provide a complete metabolic picture. At-home blood draw kit ships next day. Results in 3–5 business days. Physician interpretation call included. HSA/FSA eligible.

72 biomarkers. At-home collection. Physician interpretation. Results in 3–5 days.

Frequently Asked Questions