How to Read Your GLP-1 Lab Report: A Complete Guide to Understanding Your Blood Work

Sarah stared at the patient portal on her phone, looking at twelve different lab values her doctor had ordered before starting Semaglutide. HbA1c: 6.2%. TSH: 2.4 mIU/L. eGFR: 87 mL/min. What did any of this mean? Was she safe to start treatment? She'd been excited about finally addressing her weight and prediabetes, but now she felt overwhelmed by medical jargon she didn't understand.

If you're like Sarah, you've probably received a lab report that looks like it's written in a foreign language. Here's the truth: understanding your baseline labs isn't just about getting medical clearance. These numbers tell a story about your metabolic health, help predict how you'll respond to GLP-1 medications, and establish benchmarks you'll use to measure your progress. Let's break down exactly what each marker means and why your provider ordered it.

The Glucose Metrics: Your Metabolic Starting Point

The first thing your provider looks at is how your body handles sugar. This isn't just about whether you're diabetic—it's about understanding your entire metabolic picture before starting Semaglutide or Tirzepatide.

Your fasting glucose should ideally be below 100 mg/dL. Between 100-125 mg/dL indicates prediabetes, while 126 mg/dL or higher on two separate tests suggests diabetes. This single measurement captures just one moment in time, which is why it's paired with other markers. You might've fasted for eight hours, or maybe you only managed six. You might've been stressed about the blood draw itself, which can temporarily raise glucose levels.

That's where HbA1c comes in—your three-month glucose average. Think of it as your metabolic report card. An HbA1c below 5.7% is normal. Between 5.7-6.4% indicates prediabetes. At 6.5% or above, you meet diagnostic criteria for type 2 diabetes. This marker matters tremendously for GLP-1 therapy because the STEP 1 trial showed that participants with higher baseline A1c levels often experienced more dramatic improvements. We've seen patients drop their A1c by 1-2 full percentage points within the first three months of treatment.

Some providers also order fasting insulin, which reveals how hard your pancreas is working to control your blood sugar. High insulin with normal glucose suggests insulin resistance—your body needs to produce extra insulin to keep sugar levels in check. This is actually one of the earliest metabolic changes we can detect, often appearing years before glucose levels rise. Normal fasting insulin typically falls between 2-20 μIU/mL, though optimal levels are generally below 10 μIU/mL.

If you're already on diabetes medication, don't be surprised if your provider adjusts your doses before starting a GLP-1. These medications are powerful glucose regulators, and continuing high doses of other diabetes drugs can lead to hypoglycemia. We typically reduce or eliminate sulfonylureas and decrease basal insulin doses by 20-30% when initiating GLP-1 therapy.

Kidney Function Tests: Why Your Nephrons Matter

Your kidneys filter waste from your blood, regulate fluid balance, and perform dozens of other critical functions. They're also responsible for clearing GLP-1 medications from your system, which is why kidney function tests are non-negotiable before starting treatment.

Creatinine is a waste product from normal muscle breakdown. Your kidneys filter it out, so elevated levels suggest your kidneys aren't working efficiently. Normal ranges vary by sex and muscle mass: typically 0.6-1.2 mg/dL for men and 0.5-1.1 mg/dL for women. But here's what many patients don't realize—creatinine alone doesn't tell the whole story. A bodybuilder might have slightly elevated creatinine simply because they have more muscle mass, while an elderly patient with low muscle mass might have normal creatinine despite poor kidney function.

That's why we rely more heavily on eGFR (estimated glomerular filtration rate), which adjusts for age, sex, and race to estimate how well your kidneys filter blood. An eGFR above 90 mL/min/1.73m² is normal. Between 60-89 suggests mild reduction. Below 60 indicates chronic kidney disease, and below 30 represents severe kidney impairment. The SURMOUNT-1 trial included patients with eGFR as low as 60, and they showed similar safety profiles to those with normal kidney function.

For patients with reduced kidney function, GLP-1 medications aren't necessarily off the table. Both Semaglutide and Tirzepatide can be used in patients with eGFR above 15-30, though dosing adjustments may be needed. In fact, the SELECT trial demonstrated that Semaglutide actually improved kidney outcomes in high-risk patients, reducing the progression of kidney disease by 22%.

Some labs also include BUN (blood urea nitrogen), another waste product filtered by kidneys. Normal BUN ranges from 7-20 mg/dL. Elevated BUN can indicate kidney problems, but it can also rise from dehydration, high protein intake, or certain medications. We look at the BUN-to-creatinine ratio to distinguish between these possibilities—a ratio above 20:1 often suggests dehydration rather than kidney disease.

Pancreatic and Liver Markers: Monitoring Safety Signals

Your pancreas produces digestive enzymes and hormones like insulin. Your liver processes medications, produces proteins, and performs over 500 different functions. Both organs deserve attention before starting GLP-1 therapy.

Lipase is a pancreatic enzyme that helps digest fats. Normal levels typically range from 0-160 U/L, though this varies by laboratory. Why do we check this? Because pancreatitis—inflammation of the pancreas—is a rare but serious potential side effect of GLP-1 medications. By establishing your baseline lipase level, we can better interpret any symptoms that develop during treatment. If you experience severe abdominal pain that radiates to your back while on Semaglutide or Tirzepatide, your provider will likely recheck this value.

The actual risk is quite low. Large trials showed pancreatitis rates of about 0.2% with GLP-1 medications versus 0.1% with placebo—a tiny absolute difference. But if you have a history of pancreatitis or gallstones, your provider needs to know your baseline lipase and discuss your individual risk factors.

Liver function tests include several markers. ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes that leak from liver cells when they're damaged or inflamed. Normal ranges are typically 7-56 U/L for ALT and 10-40 U/L for AST, though men often run slightly higher than women. Mild elevations—up to two times the upper limit of normal—are common in people with fatty liver disease, which affects about 25% of adults in the United States.

Here's the interesting part: GLP-1 medications often improve liver function. We frequently see ALT and AST levels drop as patients lose weight and improve their metabolic health. The STEP 1 trial showed improvements in liver fat content and inflammation markers, even in participants who didn't have diagnosed liver disease at baseline.

Bilirubin, a breakdown product of red blood cells, should typically be below 1.2 mg/dL. Elevated bilirubin can indicate liver problems, but it can also occur with Gilbert's syndrome, a harmless genetic condition affecting about 3-7% of people. Your provider looks at the pattern of liver markers together, not just individual values.

Thyroid Function: A Critical Screening

Before starting any GLP-1 medication, you'll see TSH (thyroid stimulating hormone) on your lab order. This isn't optional—it's required screening because of a specific concern with one medication in the GLP-1 class.

In rodent studies, Semaglutide and Tirzepatide caused thyroid C-cell tumors at exposures much higher than human therapeutic doses. We don't have evidence this occurs in humans, but out of abundance of caution, these medications carry a black box warning about medullary thyroid carcinoma. If you have a personal or family history of medullary thyroid cancer or Multiple Endocrine Neoplasia syndrome type 2, GLP-1 receptor agonists are contraindicated.

TSH testing helps identify underlying thyroid dysfunction that might need treatment. Normal TSH ranges from about 0.4-4.0 mIU/L, though optimal levels for most people fall between 1.0-2.5 mIU/L. Low TSH suggests hyperthyroidism (overactive thyroid), while elevated TSH indicates hypothyroidism (underactive thyroid). Both conditions can affect your metabolism and weight, so they need to be addressed as part of your overall care plan.

What Women Should Know

Women of childbearing potential should expect a pregnancy test before starting GLP-1 therapy. Both Semaglutide and Tirzepatide are not recommended during pregnancy, and you should use reliable contraception during treatment. If you're planning to become pregnant, you'll need to stop these medications at least two months before trying to conceive.

Some providers also check prolactin and testosterone levels in women with irregular periods or polycystic ovary syndrome (PCOS). Here's something important: as you lose weight on GLP-1 therapy, your hormonal balance often shifts. We've seen patients with PCOS resume regular ovulation, which means pregnancy becomes possible even if you've had fertility challenges. This is wonderful if you're trying to conceive, but it requires planning if you're not.

What Men Should Know

Men may have testosterone checked as part of baseline labs, especially if you've mentioned fatigue, low libido, or difficulty losing weight. Low testosterone (typically below 300 ng/dL) is common in men with obesity and can make weight loss more challenging. The good news? Weight loss through GLP-1 therapy often naturally increases testosterone levels as you shed visceral fat.

Your baseline creatinine will typically run higher than women's reference ranges because you have more muscle mass on average. Don't be alarmed if your creatinine is 1.1 or 1.2 mg/dL—this is often normal for men. The eGFR calculation accounts for sex differences and gives a more accurate picture of kidney function.

From the Ozari Care Team

We recommend taking a photo of your baseline lab results and keeping them in a dedicated health folder on your phone. You'll want to compare these numbers to follow-up labs at three and six months to see your progress. In our experience, watching these markers improve—your A1c dropping, your liver enzymes normalizing, your lipid panel getting healthier—provides incredible motivation to stay consistent with treatment. What we tell our patients is this: these aren't just numbers on a page. They're measurements of your body healing at the cellular level.

Key Takeaways

• Your HbA1c and fasting glucose establish your metabolic baseline and help predict how dramatically you'll respond to GLP-1 therapy—higher baseline values often lead to more significant improvements
• Kidney function tests (creatinine and eGFR) determine medication safety and dosing, but most patients with eGFR above 60 can safely use Semaglutide or Tirzepatide without adjustments
• Baseline lipase and liver enzymes (ALT, AST) let your provider distinguish normal values from potential side effects if symptoms develop during treatment
• TSH screening is mandatory to identify thyroid conditions and ensure you don't have contraindications related to family history of medullary thyroid cancer
• Save your baseline labs to compare with future testing—watching these markers improve over time provides powerful evidence that GLP-1 therapy is working at the metabolic level

Frequently Asked Questions

Do I really need to fast for 12 hours before my GLP-1 lab work?

Most providers require an eight-hour fast, not twelve, before baseline labs. This means no food or caloric beverages after midnight if you're having blood drawn in the morning. You can drink water, black coffee, and take your usual medications unless specifically told otherwise. The fasting requirement ensures accurate glucose, insulin, and lipid measurements that aren't affected by recent meals. If you can't tolerate fasting due to medications or health conditions, talk to your provider—they may be able to work with non-fasting values or adjust the timing of your labs.

What happens if my labs come back abnormal?

It depends on which values are abnormal and by how much. Mild abnormalities like slightly elevated liver enzymes or borderline A1c don't necessarily disqualify you from GLP-1 therapy—in fact, these medications often improve these markers. However, severe kidney impairment (eGFR below 30), significantly elevated lipase, or uncontrolled thyroid disease may require treatment or further evaluation first. Your provider will discuss any concerning values with you and create a plan, which might include retesting, starting at a lower dose, or addressing the underlying issue before beginning GLP-1 therapy. We see patients with less-than-perfect labs start treatment successfully all the time.

How often will I need follow-up labs while on Semaglutide or Tirzepatide?

Standard practice involves repeat labs at three months after starting treatment, then every six months during the first year. These check-ins monitor kidney function, ensure you're not developing side effects, and document improvements in metabolic markers like A1c and lipids. If you have diabetes or kidney disease at baseline, your provider may want more frequent monitoring—some patients with diabetes get A1c checked every three months. After the first year, if everything looks stable, many patients move to annual lab work unless symptoms or concerns develop.

Why did my doctor order some tests that aren't on this list?

Providers often customize lab panels based on your individual health history, symptoms, and medications. If you're taking other medications, you might get drug levels checked. If you mentioned fatigue, you might get vitamin D, B12, or iron studies. If you have a history of heart disease, you'll likely get a complete lipid panel with particle size analysis. Some providers order inflammatory markers like CRP or metabolic markers like uric acid to get a more complete picture. These additional tests help create a personalized treatment plan and identify other factors that might affect your weight loss journey or overall health.

Can I start GLP-1 medication before all my lab results come back?

No, and here's why: certain lab abnormalities represent true contraindications or require dose adjustments before safely starting treatment. Your provider needs to see your kidney function to ensure proper dosing, your thyroid function to rule out contraindications, and your baseline metabolic markers to monitor for changes. Most labs return within 24-48 hours, and some basic metabolic panels come back the same day. While waiting feels frustrating when you're ready to start, this screening process protects your safety and ensures you get the maximum benefit from treatment. Think of it as building a strong foundation for your weight loss journey—worth the short delay.

At Ozari Health, we offer compounded Semaglutide and Tirzepatide as low as $99/month, shipped to your door. Our care team reviews your labs, answers your questions, and supports you throughout your entire treatment journey. Learn more at ozarihealth.com.