Labs to Get Before Starting Ozempic, Wegovy, or Mounjaro (GLP-1 Guide)

Medically Approved by Dr. Edward Salko

Medically Reviewed | Updated: February 2026 Category: GLP-1 & Weight Loss | Reading Time: 8 min

If you’re preparing to start a GLP-1 receptor agonist — whether that’s semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), or another agent in this class — baseline lab testing is one of the most important steps you can take before your first dose. This guide explains which blood tests to get, why each one matters, and how to order them without waiting weeks for a doctor’s appointment.

Why Baseline Labs Matter Before GLP-1 Therapy

GLP-1 receptor agonists are among the most effective metabolic medications available today. Clinical trials show semaglutide produces an average body weight reduction of 15% or more, and tirzepatide produces reductions exceeding 20% in some populations. But these medications interact with multiple organ systems, the pancreas, kidneys, thyroid, and liver chief among them. Starting without a documented baseline creates two significant problems.

First, pre-existing conditions in those organ systems may represent contraindications or risk factors that affect whether GLP-1 therapy is appropriate for you. Second, without a pre-treatment measurement, there is no way to distinguish a medication-related change in your labs from a change that was already present before you started. Your baseline is your reference point for everything that follows.

Prescribers typically request lab work completed within the past six months before initiating GLP-1 therapy. If your last blood panel was more than six months ago or if you’ve never had a comprehensive metabolic workup getting current results before starting is the standard of care.

The Core Panel: Blood Tests Most Providers Require

1. Hemoglobin A1c (HbA1c)

Why it matters: HbA1c reflects your average blood glucose over the prior two to three months and is the single most important baseline marker for anyone starting a GLP-1 agent. It establishes your glycemic status before treatment, confirms whether you have prediabetes or type 2 diabetes (which affects both the prescription pathway and insurance coverage), and creates a benchmark against which your provider will track therapeutic response. If your A1c is already elevated, read our detailed guide on what it means if your Hemoglobin A1c is high and how to lower it to understand potential causes and next steps before starting therapy.

GLP-1 medications lower A1c significantly in people with elevated levels. Clinical trial data from the STEP program showed that people with prediabetes at baseline achieved normal A1c in 84–85% of cases after 68 weeks of semaglutide. Without a pre-treatment A1c, that improvement is invisible.

Normal reference range: Below 5.7% (prediabetes: 5.7–6.4%; diabetes: 6.5% and above)

2. Fasting Glucose

Why it matters: While A1c provides a longer-term picture, fasting glucose captures your blood sugar at a single point in time and can reveal patterns that A1c may miss particularly in people with certain hemoglobin variants that affect A1c accuracy. It also establishes your baseline hypoglycemia risk, which is relevant if you are taking other glucose-lowering agents alongside a GLP-1 medication.

Normal reference range: 70–99 mg/dL (fasting)

3. Comprehensive Metabolic Panel (CMP)

Why it matters: The CMP is arguably the most essential single panel before GLP-1 initiation because it assesses both kidney function and liver function simultaneously — the two organ systems most relevant to medication safety monitoring.

Kidney function (creatinine, BUN, eGFR): GLP-1 medications have been associated with rare cases of acute kidney injury, typically linked to dehydration from gastrointestinal side effects such as nausea and vomiting. Pre-existing renal impairment is a critical factor in prescribing decisions. Your eGFR establishes where your kidneys are functioning before treatment begins.

Liver enzymes (ALT, AST): Elevated liver enzymes before starting GLP-1 therapy — common in people with non-alcoholic fatty liver disease, which frequently accompanies the metabolic conditions these medications treat — need to be documented. Research shows liver enzymes often improve during GLP-1 treatment as weight loss reduces hepatic fat accumulation, but only a documented baseline makes that improvement verifiable.

Electrolytes: Rapid weight loss and reduced food intake can affect sodium, potassium, and magnesium balance. A pre-treatment electrolyte panel identifies any existing imbalances before the medication is added to the picture.

4. Lipid Panel (Total Cholesterol, LDL, HDL, Triglycerides)

Why it matters: Many patients initiating GLP-1 therapy have elevated triglycerides or dyslipidemia as part of their broader metabolic picture. GLP-1 agents have been shown to improve lipid profiles — reducing total cholesterol, LDL, and triglycerides while raising HDL in many patients. A pre-treatment lipid panel documents your cardiovascular risk baseline and enables your provider to measure this improvement over time.

For patients with established cardiovascular disease, baseline lipids also inform the overall risk-benefit calculation for GLP-1 therapy, which has demonstrated cardiovascular outcome benefits in high-risk populations.

5. Complete Blood Count (CBC)

Why it matters: A CBC with differential provides a baseline assessment of red blood cells, white blood cells, and platelets. GLP-1 medications are not known to cause primary hematologic effects, but the significant dietary changes and reduced caloric intake that accompany treatment can affect iron stores and B12 levels over time. A CBC at baseline identifies any pre-existing anemia or other blood abnormalities that could complicate your treatment course.

6. Thyroid Function (TSH)

Why it matters: This is one of the most clinically significant pre-treatment tests for GLP-1 therapy. The FDA prescribing information for semaglutide-based medications includes a boxed warning regarding the potential risk of thyroid C-cell tumors (medullary thyroid carcinoma, or MTC) observed in rodent studies, though human relevance has not been established. Regardless, GLP-1 medications are contraindicated in patients with a personal or family history of MTC or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

Beyond the contraindication question, hypothyroidism is a common and frequently underdiagnosed condition that causes weight gain, fatigue, and metabolic slowdown — symptoms that may be mistakenly attributed to poor GLP-1 response if thyroid dysfunction is not identified and treated. A TSH (thyroid-stimulating hormone) test at baseline screens for both hypothyroidism and hyperthyroidism before attributing any metabolic changes to the medication.

Additional Tests Worth Considering

Fasting Insulin & HOMA-IR

Fasting insulin levels are among the most sensitive available markers for insulin resistance — the metabolic condition that underlies both type 2 diabetes and obesity in many patients. Insulin resistance can be present for years before A1c or fasting glucose become abnormal, which means standard glucose tests may appear normal while significant metabolic dysfunction is already underway. Despite its clinical value, fasting insulin is not routinely ordered by most primary care providers. Getting it at baseline provides a more complete picture of your metabolic health and helps quantify your response to GLP-1 treatment over time.

hsCRP (High-Sensitivity C-Reactive Protein)

Inflammatory burden is an important driver of metabolic disease and cardiovascular risk. hsCRP is a sensitive marker of systemic inflammation that frequently decreases with GLP-1 treatment and weight loss. Establishing a pre-treatment baseline allows you and your provider to track this improvement as a distinct measure of therapeutic benefit beyond weight loss alone.

Uric Acid

GLP-1 therapy and the associated caloric restriction can affect uric acid levels. In patients with gout or hyperuricemia, a pre-treatment baseline helps distinguish medication effects from pre-existing conditions. This test is inexpensive and adds meaningful context for metabolic monitoring.

Vitamin B12

Reduced appetite and caloric intake during GLP-1 treatment can lead to nutritional deficiencies over time. Vitamin B12 deficiency is particularly relevant in older patients and in anyone taking metformin concurrently, as metformin is known to reduce B12 absorption. A baseline level identifies pre-existing deficiency before the medication is initiated.

Ongoing Monitoring Schedule

Starting GLP-1 therapy is the beginning of a monitoring relationship, not a one-time event. Most clinical guidance recommends:

At 3 months: A1c recheck (HbA1c reflects the prior 3-month average, making this the earliest timepoint for meaningful assessment of glycemic response), metabolic panel if any GI side effects were significant
At 6 months: Full panel repeat — A1c, CMP, lipids, CBC — to document treatment response comprehensively
Annually: Full panel plus thyroid function, B12, and any additional markers relevant to your individual health picture

If you experience severe or persistent gastrointestinal side effects, signs of dehydration, unusual fatigue, or any concerning symptoms, kidney function should be rechecked without waiting for a scheduled interval.

GLP-1 Baseline Lab Checklist

Test	Why It Matters	Required By Most Providers?
HbA1c	Establishes blood sugar baseline	Yes
CMP	Evaluates kidney & liver safety	Yes
TSH	Screens thyroid function	Yes
Lipid Panel	Documents cardiovascular risk	Often
CBC	Identifies baseline anemia	Often

Frequently Asked Questions

Do I need a doctor’s order to get these labs? In most U.S. states, you can order your own lab tests directly without a physician’s order. Direct-access laboratory testing allows you to get results quickly, often at significantly lower cost than through traditional channels, and without waiting for an appointment.

How current do my labs need to be before starting a GLP-1 medication? Most prescribers will accept lab results from within the past six months. Results older than six months are typically repeated before initiating treatment, since metabolic markers can change meaningfully in that window.

Which tests are most important if I can only do a few? If you need to prioritize, the three most critical baseline tests are HbA1c, a Comprehensive Metabolic Panel, and TSH. These three together address glycemic status, organ function safety screening, and the thyroid contraindication question.

Will insurance cover these tests? Coverage varies depending on your plan and diagnosis codes. Many patients find it faster and more cost-effective to order baseline labs directly, particularly when they want results quickly and don’t want to navigate referral processes or insurance prior authorization.

What if my labs show something abnormal? Abnormal results before starting GLP-1 therapy are not necessarily disqualifying — they are informative. Mildly elevated liver enzymes, impaired kidney function, or thyroid dysfunction may require further evaluation or treatment before or alongside GLP-1 initiation. Your prescribing provider uses this information to make the safest possible treatment decision for your specific situation.

Why Telehealth Providers Often Skip Baseline Labs

Some telehealth platforms initiate GLP-1 therapy without requiring comprehensive baseline lab testing. While convenient, skipping pre-treatment labs can delay identification of underlying thyroid dysfunction, kidney impairment, or metabolic abnormalities that may influence medication safety and dosing. Independent baseline testing ensures you begin therapy with a complete clinical picture.

Order Your Pre-GLP-1 Baseline Labs Today

Personalabs offers direct-access lab testing through a nationwide network of over 4,000 Labcorp patient service centers. No doctor’s visit required, no insurance required. Order online, get tested at a location near you, and receive results typically within 1–3 business days.

Relevant tests available at Personalabs:

This article is for informational purposes only and does not constitute medical advice. Lab testing should be used in conjunction with guidance from a qualified healthcare provider. GLP-1 medications require a valid prescription from a licensed clinician.