What Blood Tests Should You Get Before Starting GLP-1 Therapy?

A man came into my Southlake office in July carrying a vial of compounded semaglutide he'd bought from an online outfit two states away. No labs. No exam. A web form, a credit card, and the medication showed up at his house in Colleyville three days later. Six weeks in, he'd dropped eleven pounds and felt awful. Not queasy awful. Wrung out, foggy, couldn't-finish-a-set awful.

His bloodwork explained it in about four minutes. Ferritin in the basement. A TSH drifting well past where I'd want it. Total testosterone of 214. The GLP-1 was doing exactly what GLP-1s do. Everything underneath it was not.

That's the argument for testing first, in one patient. The medication is genuinely good. The medication is also blind. It doesn't know what your thyroid is up to, whether your pancreas has a history, or whether the fatigue you're about to blame on "the shot" was already sitting in your labs six months ago. So here's the panel, what each piece is doing there, and what your starting numbers say about how you're likely to respond.

What Is a Baseline GLP-1 Panel Actually Screening For?

A baseline panel before semaglutide or tirzepatide does three jobs at once: it rules out the handful of conditions that make a GLP-1 unsafe, it measures the metabolic problem you're actually treating, and it captures a starting point so that three months later we can prove the medication worked instead of guessing from the bathroom scale.

Those three jobs matter in that order. Safety first, then diagnosis, then measurement. Most men fixate on the third one because the scale is the thing they can see. I care most about the first two, because that's where a physician earns his keep.

The panel I order runs roughly fifteen markers. It's one blood draw, eight to twelve hours fasted, water only. At our Southlake lab partners most of it results inside 24 to 48 hours, so nobody waits a month to start. Every man who enrolls in our GLP-1 weight loss program in Southlake gets this draw before his first injection, no exceptions. Here's how it breaks down.

Which Metabolic Markers Come First?

Hemoglobin A1c, fasting glucose, and fasting insulin form the core. Together they show where you sit on the road from normal metabolism to prediabetes to type 2 diabetes. Fasting insulin is the one most primary care panels skip, and it's usually the earliest number to go wrong in men.

A1c gives us your average blood sugar over roughly three months. Fasting glucose is a single snapshot. Neither one, on its own, catches the man whose pancreas is working overtime to keep his glucose looking normal. That's what fasting insulin is for.

I've had men in Grapevine and Trophy Club come in with a perfectly respectable A1c of 5.4 and a fasting insulin of 22. Their sugar looked fine because their pancreas was screaming to keep it there. That pattern is insulin resistance, and it's the exact physiology a GLP-1 is built to interrupt. Finding it pre-treatment tells me a lot about dosing and about how fast to expect movement.

The lipid panel and why triglycerides get special attention

Full lipids go on the panel too: total cholesterol, LDL, HDL, triglycerides. Triglycerides carry extra weight here for two reasons. First, a triglyceride-to-HDL ratio above about 3 is a decent fingerprint for insulin resistance in men, and it costs nothing extra to calculate. Second, severely elevated triglycerides raise pancreatitis risk on their own, which matters for the pancreas conversation below.

Triglycerides also tend to be the marker that moves first and moves hard once treatment starts. Men who watch their numbers like a stock ticker (and plenty of my patients do) usually get their first real win here, well before the waistline catches up.

Why Does Your Thyroid Matter Before a GLP-1?

Two reasons. An underactive thyroid produces fatigue, weight gain, and sluggish metabolism that no GLP-1 will correct, so it needs its own treatment. And GLP-1 receptor agonists carry a boxed warning tied to medullary thyroid carcinoma, which means personal or family history has to be asked about directly.

I order TSH and free T4 on everybody, and add thyroid antibodies when the history or the TSH suggests autoimmune thyroid disease. If your thyroid is undertreated, you can lose weight on a GLP-1 and still feel flat the entire time, which is a miserable way to spend six months. Treat the thyroid, then judge the medication honestly. There's a similar interplay on the hormone side, which I covered in more detail in the piece on how TRT and thyroid function overlap.

The carcinoma piece is a history question more than a lab one. GLP-1 receptor agonists are not prescribed to people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia type 2. That's a hard line, and it's one of the specific things I'm asking about at the first visit rather than leaving to a checkbox on an intake form.

What Do the Pancreas, Liver, and Kidney Numbers Tell Us?

A complete metabolic panel covers liver enzymes, kidney function, and electrolytes. Lipase gets added for men with any history of pancreatitis, gallstones, or heavy alcohol use. These aren't formalities. They set dosing pace, flag who needs closer monitoring, and catch fatty liver disease, which is quietly common in men over forty.

Start with the liver. Elevated ALT and AST in a man carrying extra abdominal weight usually means metabolic fatty liver, and that's good news in a strange way: GLP-1 therapy tends to improve it. But I want the starting enzymes on record so that a rise later gets investigated instead of shrugged at.

Kidneys next. Creatinine and eGFR guide how carefully we titrate. The nausea and reduced fluid intake that can come with the first few weeks of therapy are manageable in a man with normal kidney function and require a slower, closer approach in a man without. That's a monitoring decision, and you can only make it if you have the number.

Pancreatitis history changes the conversation

Pancreatitis is a listed adverse event for this drug class. A man with prior pancreatitis or symptomatic gallstones isn't automatically excluded, but he gets a different discussion, a baseline lipase, and tighter follow-up. If you want the fuller picture of what to expect physically once dosing begins, I wrote about that in the side effects men should actually plan for.

Should Men Check Testosterone Before Starting a GLP-1?

Yes, and it's the marker most weight-loss clinics leave off entirely. Adipose tissue converts testosterone into estradiol through aromatase, so men carrying significant fat mass frequently test low. Knowing the starting number tells us whether hormones recover on their own with weight loss or need direct support.

Total testosterone, free testosterone, SHBG, and estradiol go on the panel. This is where men's weight loss diverges sharply from the generic protocol, and it's the part I'd most want a friend to insist on.

Here's the mechanism. Fat tissue, especially visceral fat around the abdomen, is metabolically busy. It expresses aromatase, which converts testosterone into estradiol. More fat, more conversion, less circulating testosterone, more fat storage. The loop feeds itself, which is why stubborn belly fat in men so often coexists with hormone numbers in the tank.

Weight loss alone breaks part of that loop. Plenty of men see testosterone climb meaningfully after dropping fifteen percent of their body weight, and that's the outcome I'm hoping for. Others don't recover, usually because the underlying problem was testicular or pituitary rather than fat-driven. The only way to sort those two groups is to measure at the start and remeasure at twelve weeks. There's more on how the two therapies interact in this post on GLP-1s and testosterone levels, and on running them together in the combined-therapy article.

What About Iron, B12, and the Blood Count?

A CBC with ferritin and B12 catches the deficiencies that mimic side effects. Low ferritin looks like GLP-1 fatigue. Low B12 looks like GLP-1 brain fog. Correcting them before treatment means that when a man tells me he's tired at week four, I know where to look.

The patient I opened with is the case study. His ferritin was 14. He'd have blamed the medication for another three months, tapered off, and concluded that GLP-1s "didn't work for him." Iron repletion plus the semaglutide, and by September he was down twenty-six pounds and back to lifting four days a week.

Vitamin D goes on the panel as well. It's inexpensive, deficiency is common even in North Texas (we spend the hot months indoors, same as everyone), and it sits at the intersection of energy, mood, and testosterone production.

Who Gets the Most Out of a Physician-Run GLP-1 Program?

The man who benefits most is the one whose labs show real insulin resistance, a metabolic pattern that diet alone hasn't shifted, and hormone numbers worth tracking. For him, testing first turns a generic prescription into a plan with a target, a timeline, and a way to prove it's working.

If that's you, the labs are what make the difference between a shot and a program. Preserving muscle while you lose fat, for example, depends on protein intake, resistance training, and monitoring that a mail-order vial simply doesn't include. I laid out that approach in how men can protect lean mass on a GLP-1.

When you're comparing options around DFW, ask three specific questions. Does the program include baseline and follow-up lab work, or just the medication? Does a physician review the results with you? And if it's compounded, where does it come from and can they show you the pharmacy's credentials? That last one deserves real scrutiny, and I walked through how to check in this guide to verifying your compounding pharmacy. Our medically supervised weight loss program builds all three in, and the same protocol runs at our Keller GLP-1 clinic for patients on that side of 114.

For the longer version of everything here, including dosing schedules and food strategy, the GLP-1 weight loss guide for men is the place to start. If you're still comparing clinics, our roundup of the best GLP-1 weight loss clinics in DFW for 2026 lays out what to look for.

Frequently Asked Questions

Some online services will send a vial after a questionnaire. A baseline panel is what lets your physician dose safely, catch a thyroid or pancreatic issue early, and prove the medication is working rather than guessing from the scale.

Most of the panel results within 24 to 48 hours at our Southlake lab partners. We typically review results and start dosing inside the same week, so testing rarely delays treatment.

Yes. Fast eight to twelve hours with water only. Fasting insulin, glucose, and triglycerides are the numbers that shift most with food, and those three drive a lot of the treatment plan.

Absolutely. Excess body fat converts testosterone to estradiol, so low readings are common before weight loss. Knowing the starting number tells us whether hormones recover on their own or need direct support.

We recheck at roughly twelve weeks, then every six months on a stable dose. Follow-up panels are shorter than the baseline and focus on A1c, metabolic chemistry, lipids, and hormones.

If you're thinking about a GLP-1 and you'd like to see the full picture before the first dose, come in. The first visit is free, it includes a testosterone check and a body composition scan, and you'll leave knowing what your numbers actually say. Book a consultation and we'll go through them together.