Bloodwork should come before your first dose of a GLP-1. A basic lab panel tells your provider whether a medication like semaglutide or tirzepatide is appropriate for you, which starting dose makes sense, and whether something else, like an underactive thyroid or creeping blood sugar, has been working against your weight all along.
Plenty of online programs will ship medication to your door after a five-minute questionnaire. Before you sign up anywhere, ask what they checked first.
The Quick Answer
Before starting a GLP-1 like semaglutide or tirzepatide, most providers check a metabolic panel (kidney and liver function, blood glucose), an A1C, a lipid panel, and thyroid function (TSH). These labs screen for conditions that change how a GLP-1 should be prescribed and give you a baseline to measure real progress against. At Defiant in Lisle, IL, lab review is built into every GLP-1 program: we write the order, you complete the draw through your PCP or Rythm Health, and your provider walks through the results with you before your protocol starts.
Why Labs Come Before the Prescription
GLP-1 medications are effective. In the STEP 1 trial, adults on 2.4 mg of semaglutide lost an average of 14.9% of their body weight over 68 weeks,1 and in SURMOUNT-1, participants on the highest dose of tirzepatide lost an average of 20.9% over 72 weeks.2 Numbers like that are why demand has exploded, and why so many programs now hand out prescriptions with almost no workup.
Skipping the workup is a problem. A GLP-1 changes how your body handles glucose, digestion, and appetite, so your provider needs to know what your body is doing before the medication starts changing it. If your thyroid is underactive, that's a separate issue worth addressing, and it may explain weight that hasn't budged with diet changes. If your A1C sits in the diabetic range, your medication plan and monitoring look different than they would for someone with normal blood sugar. If your kidney or liver values are off, your provider wants to know that on day one, not month three. If you're not sure you're even a candidate, our guide to who qualifies for a GLP-1 walks through the criteria.
You also can't measure improvement without a starting point. Baseline labs let you see your A1C, lipids, and metabolic markers actually move over the course of your program, which matters because research suggests GLP-1s may support improvements in several of those markers alongside weight loss.1 Watching your bloodwork improve is a very different experience than watching a number on a scale.
What the Panel Actually Checks
The exact panel is tailored to your history, but a typical pre-GLP-1 workup covers this ground:
| Lab | What it tells your provider |
|---|---|
| A1C and fasting glucose | Where your blood sugar sits: normal, prediabetic (A1C 5.7 to 6.4%), or diabetic (6.5%+)3 |
| Comprehensive metabolic panel (CMP) | Kidney function, liver enzymes, and electrolytes, which affect how your body processes medication |
| Lipid panel | Cholesterol and triglycerides, a baseline for tracking metabolic improvement |
| TSH (thyroid) | Whether an underactive or overactive thyroid is influencing your weight or energy |
| CBC (complete blood count) | General screen for anemia and other issues worth knowing about first |
Your provider may add markers based on your history, like fasting insulin if insulin resistance is suspected. And separate from labs, your intake covers the history questions that matter for GLP-1s specifically: per FDA labeling, these medications are contraindicated for anyone with a personal or family history of medullary thyroid carcinoma or MEN 2, and a history of pancreatitis calls for extra caution.4
Some of these results open their own conversations. If your A1C lands in the prediabetic range, our post on GLP-1s and prediabetes covers what that means. Elevated liver enzymes connect to GLP-1s and fatty liver, and the kidney values to GLP-1s and kidney health.
What Your Results Change
Bloodwork isn't a formality that ends in the same prescription either way. Results shape real decisions.
They influence which medication fits you best. Semaglutide and tirzepatide work through related but different mechanisms, and your glucose picture, your history, and your goals all factor into the choice. If you're weighing the two, the comparison in tirzepatide vs semaglutide covers how they differ.
They influence your starting dose and how quickly it moves. Every Defiant protocol titrates bi-weekly rather than monthly, so your dose gets adjusted based on how you're actually responding. Labs give that process an informed starting point instead of a guess.
And sometimes they surface something more important than the prescription itself. A thyroid result or a liver value outside the normal range is worth knowing regardless of your weight goals, and it's the kind of finding a questionnaire-only program will never catch. When something needs a closer look, we'll say so and point you to the right follow-up.
How Bloodwork Works at Defiant
We don't draw blood in the clinic.
Your GLP-1 program starts with a $50 consultation at our Lisle office. From there, your provider writes the lab order and you complete the draw wherever is convenient, either through your own PCP or through Rythm Health. If you use our Rythm Health referral link, you save $20 on the draw. Results typically come back within days, and your provider reviews them with you before your protocol begins.
Labs are one of two baselines we set. The other is a Styku 3D body composition scan, which tracks fat and lean mass monthly so your progress is measured in body composition, not just pounds. From there, your program runs from $295 a month and includes the medication, provider oversight, bi-weekly titration, monthly scans, and weekly nurse check-ins. Research suggests medically supervised programs with ongoing monitoring may support better long-term outcomes than medication alone, and the labs are where that supervision starts.
We serve Lisle, Naperville, Downers Grove, Wheaton, and Chicago's western suburbs.
- Baseline bloodwork before a GLP-1 screens for conditions that change how the medication should be prescribed, including thyroid dysfunction, elevated blood sugar, and kidney or liver issues.
- A typical panel includes an A1C, comprehensive metabolic panel, lipid panel, TSH, and CBC, tailored to your history.
- Lab results influence medication choice, starting dose, and monitoring, and they give you a baseline to measure metabolic improvement against.
- Per FDA labeling, GLP-1s are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2, which is screened at intake.
- Defiant writes the lab order and reviews results with you; the draw happens through your PCP or Rythm Health (the referral link saves $20). Programs start at $295/mo.
Frequently Asked Questions
Start With Your Biology.
Every Defiant GLP-1 protocol begins with labs, a body composition scan, and a real conversation with a provider. The consultation is $50.
Keep Reading
Last updated October 27, 2026.
References
- Wilding JPH, Batterham RL, Calanna S, et al; STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021;384(11):989-1002. PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al; SURMOUNT-1 Investigators. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. PubMed
- American Diabetes Association. Standards of Care in Diabetes (2026): Diagnosis and Classification. ADA
- U.S. Food and Drug Administration. Semaglutide 2.4 mg injection prescribing information (boxed warning and contraindications). FDA label