What Labs Should You Do?

You started taking a GLP-1 medication for weight loss and you are wondering whether you need lab work. Your friend mentioned their doctor checks their kidney function every few months. Someone online said you absolutely need baseline labs before starting. Another person says labs are unnecessary. The conflicting information is confusing, and you want to know what is actually required versus what is optional.

Here is the straightforward answer: labs are not required to receive or continue GLP-1 medications for weight management. You can successfully take semaglutide or tirzepatide without any blood testing. However, some patients and providers find that certain lab tests provide helpful information for monitoring progress, tracking metabolic improvements, or catching potential issues early. The decision about whether to do lab testing should be made collaboratively between you and your provider based on your individual health situation, goals, and circumstances.

This article explains what biomarkers can optionally be monitored on GLP-1 therapy and why, who might benefit from testing versus who likely does not need it, what baseline and ongoing monitoring might involve if you choose to do it, and how to decide what makes sense for your situation.

Understanding the Difference: Required Versus Optional

Before discussing specific tests, it is crucial to understand that lab monitoring on GLP-1 medications exists on a spectrum from not needed to potentially helpful to medically necessary in specific situations.

Not required for most people: If you are healthy aside from weight concerns, have no chronic conditions, are not taking other medications that interact with GLP-1s, and are tolerating treatment well, you may not benefit from routine lab testing. Many people successfully use these medications with excellent outcomes without any blood work.

Potentially helpful for some: If you have certain health conditions, take medications that might interact, want to track metabolic improvements beyond the scale, or have specific health goals, selective lab testing might provide valuable information. This is a personal choice made with your provider.

Medically necessary in specific situations: If you have diabetes and take insulin or sulfonylureas (which can cause low blood sugar when combined with GLP-1s), blood sugar monitoring becomes important for safety. If you have kidney disease, periodic kidney function checks help ensure GLP-1s are not worsening kidney health. If you have certain other medical conditions, targeted monitoring makes medical sense.

The key is that testing should be individualized based on your health needs, not automatically imposed on everyone taking these medications.

Biomarkers That Can Be Monitored: What and Why

If you and your provider decide that lab monitoring would be helpful for your situation, here are the biomarkers most commonly considered and the rationale for each.

Blood Sugar Control: A1C and Glucose

What it measures: Hemoglobin A1C reflects your average blood sugar over the past two to three months. Fasting glucose measures blood sugar at a single point in time.

Why it might be helpful: If you have prediabetes or diabetes, these markers track whether your blood sugar is improving with treatment. For people without diabetes, A1C can confirm that blood sugar remains in the healthy range during weight loss. Some people find it motivating to see A1C normalize from prediabetes levels.

Who might benefit: People with diabetes or prediabetes who want to track glucose improvements. People with family history of diabetes monitoring for risk.

Who likely does not need it: People with no diabetes risk factors and normal baseline blood sugar.

Kidney Function: Creatinine, eGFR, BUN

What it measures: Creatinine is a waste product filtered by kidneys. eGFR (estimated glomerular filtration rate) estimates how well kidneys are filtering. BUN (blood urea nitrogen) measures another waste product.

Why it might be helpful: GLP-1 medications can occasionally cause dehydration through nausea, vomiting, or reduced fluid intake. Dehydration stresses kidneys. Monitoring kidney function helps catch any decline early, particularly in people with existing kidney disease or risk factors.

Who might benefit: People with pre-existing kidney disease or reduced kidney function. People with diabetes (which affects kidney health over time). People experiencing significant GI side effects that might cause dehydration.

Who likely does not need it: Young, healthy people with no kidney disease risk factors and good hydration.

Liver Function: ALT, AST

What it measures: ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes that leak into blood when liver cells are damaged or inflamed.

Why it might be helpful: Many people with obesity have fatty liver disease. Weight loss generally improves liver health, and monitoring liver enzymes can document this improvement. Some studies show GLP-1s reduce ALT levels, with maximum impact around 30 weeks of treatment.

Who might benefit: People with known fatty liver disease or elevated baseline liver enzymes. People with history of liver disease. Those who want to track liver health improvements with weight loss.

Who likely does not need it: People with no liver disease and normal liver function.

Lipid Panel: Cholesterol and Triglycerides

What it measures: Total cholesterol, LDL (bad cholesterol), HDL (good cholesterol), and triglycerides.

Why it might be helpful: Weight loss typically improves lipid profiles. Monitoring can document improvements in cardiovascular risk factors. Some people find it motivating to see cholesterol levels improve with treatment.

Who might benefit: People with high cholesterol or cardiovascular disease. People taking statins who might be able to reduce doses with weight loss. Anyone interested in tracking cardiovascular risk improvements.

Who likely does not need it: Young people with no cardiovascular risk factors and normal baseline lipids.

Thyroid Function: TSH

What it measures: TSH (thyroid-stimulating hormone) indicates whether your thyroid is producing appropriate amounts of hormone.

Why it might be helpful: Some evidence suggests weight loss can affect thyroid hormone requirements in people taking levothyroxine. For people with hypothyroidism, monitoring TSH during significant weight loss helps determine if medication doses need adjustment.

Who might benefit: People with hypothyroidism taking levothyroxine, especially during active weight loss. People with family history of thyroid disease.

Who likely does not need it: People without thyroid conditions and no thyroid medication use.

Vitamin and Mineral Levels

What it measures: Various tests measure vitamin B12, vitamin D, iron/ferritin, and magnesium levels.

Why it might be helpful: Eating significantly less food can lead to nutrient deficiencies over time, particularly if you are not consciously focusing on nutrient-dense choices. B12, vitamin D, iron, and magnesium are commonly deficient even in the general population and may become more so with reduced food intake.

Who might benefit: People eating very limited amounts or very restricted diets. People with symptoms of deficiency (fatigue, weakness, hair loss). People interested in optimizing nutrition during weight loss.

Who likely does not need it: People eating varied, nutrient-dense diets and taking multivitamins without symptoms of deficiency.

Making the Decision: Do You Need Lab Testing?

The choice about lab monitoring should be based on your individual circumstances through conversation with your provider.

Questions to guide the decision: Do you have any chronic health conditions like diabetes, kidney disease, liver disease, or thyroid disorders? Are you taking other medications that might interact with GLP-1s or require monitoring? Do you have cardiovascular risk factors where tracking improvements would influence other treatment decisions? Are you experiencing significant side effects that might affect organ function? Do you want objective data about metabolic improvements beyond weight alone?

If you answered yes to several of these questions, selective lab monitoring might provide valuable information. If you answered no to most or all, you likely do not need routine testing.

Cost considerations matter: Lab testing costs money, and not all insurance plans cover labs for weight management when diabetes is not present. If cost is a barrier, it is perfectly acceptable to skip testing and monitor your health through clinical signs and symptoms instead. You do not need labs to use GLP-1 medications successfully.

Symptoms trump labs: Regardless of whether you do lab testing, pay attention to how you feel. If you develop new symptoms (persistent nausea and vomiting, signs of dehydration, unusual fatigue, changes in urination, yellowing of skin or eyes), contact your provider regardless of whether you have recent lab work.

If You Choose to Start Monitoring

If you and your provider decide that some baseline testing makes sense before starting GLP-1 therapy, common initial tests might include:

A comprehensive metabolic panel (CMP) covering kidney function, liver enzymes, electrolytes, and glucose. Hemoglobin A1C if you have diabetes, prediabetes, or risk factors. Lipid panel if you have cardiovascular risk or high cholesterol. TSH if you have thyroid conditions or take thyroid medication. These baseline values provide comparison points for monitoring changes during treatment.

Some providers also check vitamin D, B12, and iron at baseline if nutritional deficiencies are suspected, though this is optional.

The decision about which baseline tests (if any) should be based on your individual health history and goals, not a standardized protocol applied to everyone.

Ongoing Monitoring: Frequency and Selection

If you start with baseline testing, ongoing monitoring frequency depends on what you are tracking and why.

For people with diabetes: A1C every three to six months helps track blood sugar improvements. More frequent testing makes sense if your diabetes treatment is changing or you are not meeting glucose targets. Less frequent testing (every six months) is appropriate when blood sugar is stable and well-controlled.

For people with kidney or liver concerns: Kidney and liver function tests every three to six months during active weight loss, then less frequently once weight stabilizes. More frequent monitoring if baseline function is abnormal.

For people tracking metabolic improvements: Lipid panels every six to 12 months can document cardiovascular risk factor improvements. A1C at six to 12 months can show whether prediabetes is resolving.

For people on thyroid medication: TSH every three to six months during active weight loss if taking levothyroxine, as weight changes can affect thyroid hormone requirements.

These are general patterns, not requirements. Your provider can help determine what monitoring schedule (if any) makes sense for your situation.

What Improvements You Might See in Labs

For people who do choose lab monitoring, understanding what improvements are commonly seen helps set expectations.

GLP-1 medications in people with prediabetes often improve A1C into the normal range (below 5.7%). Clinical trials showed 84% to 85% of people with baseline prediabetes achieved normal A1C after 68 weeks of semaglutide treatment.

Weight loss generally improves lipid profiles with decreases in total cholesterol, LDL cholesterol, and triglycerides, and increases in HDL (good) cholesterol. These changes reduce cardiovascular risk.

Liver enzymes (ALT, AST) often improve in people with fatty liver disease as weight loss reduces liver fat. Studies show maximum ALT reduction occurs around 30 weeks of GLP-1 treatment.

Inflammatory markers like high-sensitivity C-reactive protein (hsCRP) typically decrease with weight loss and GLP-1 treatment, reflecting reduced systemic inflammation.

For people with diabetes taking GLP-1s, kidney function markers like urine albumin-to-creatinine ratio may improve, suggesting kidney protective effects, though the magnitude of benefit is less than with some other diabetes medications like SGLT2 inhibitors.

Not everyone sees identical improvements. Individual results vary based on baseline health status, amount of weight lost, lifestyle changes, and other factors.

The Bottom Line

Lab testing on GLP-1 medications is a tool, not a requirement. For many people taking these medications for weight loss, clinical monitoring (how you feel, weight trends, side effects) provides sufficient information without lab work.

For others with specific health conditions or goals, selective lab testing offers valuable data that guides treatment decisions and documents health improvements. The key is making informed decisions about what monitoring makes sense for your individual situation rather than following a one-size-fits-all protocol.

At Mochi Health, we recognize that every person's health journey is unique. Our providers work with you to determine what monitoring (if any) makes sense based on your health status, goals, and preferences. Labs are never required for GLP-1 treatment, but if you and your provider decide testing would be helpful, we can facilitate appropriate lab orders. The decision is always based on shared decision-making about what serves your individual needs.

Beyond GLP-1 medications, we offer comprehensive weight management support including registered dietitian nutritionists who can help ensure you are meeting nutritional needs during weight loss, and access to medications that support various aspects of your health. You can explore treatment options at https://joinmochi.com/medications.

Check Your Eligibility

If you want to learn whether GLP-1 treatment is right for you and receive personalized guidance from providers who understand individualized approaches to monitoring and care, you can start by completing Mochi's eligibility questionnaire. Check your eligibility here: https://app.joinmochi.com/eligibility.

References

American Diabetes Association. (2023). Standards of medical care in diabetes—2023. Diabetes Care, 46(Supplement 1), S1-S291. https://doi.org/10.2337/dc23-Sint

Davies, M., Færch, L., Jeppesen, O. K., Pakseresht, A., Pedersen, S. D., Perreault, L., Rosenstock, J., Shimomura, I., Viljoen, A., Wadden, T. A., & Lingvay, I. (2021). Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): A randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial. The Lancet, 397(10278), 971-984. https://doi.org/10.1016/S0140-6736(21)00213-0

Garvey, W. T., Frias, J. P., Jastreboff, A. M., le Roux, C. W., Sattar, N., Aizenberg, D., Mao, H., Zhang, S., Ahmad, N. N., Bunck, M. C., Benabbad, I., Zhang, X. M., Hope, K., Haluzík, M., & SURMOUNT-2 Investigators. (2023). Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): A double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. The Lancet, 402(10402), 613-626. https://doi.org/10.1016/S0140-6736(23)01200-X

National Kidney Foundation. (2025). GLP-1 receptor agonists (GLP-1 RAs). https://www.kidney.org/kidney-topics/glp-1-receptor-agonists-glp-1-ras

Perreault, L., Davies, M., Frias, J. P., Laursen, P. N., Lingvay, I., Machineni, S., Varbo, A., Wilding, J. P. H., Wallenstein, S. O. R., & le Roux, C. W. (2023). Changes in glucose metabolism and glycemic status with once-weekly subcutaneous semaglutide 2.4 mg among participants with prediabetes in the STEP program. Diabetes Care, 46(12), 2252-2262. https://doi.org/10.2337/dc21-1785

Wilding, J. P. H., Batterham, R. L., Calanna, S., Davies, M., Van Gaal, L. F., Lingvay, I., McGowan, B. M., Rosenstock, J., Tran, M. T. D., Wadden, T. A., Wharton, S., Yokote, K., Zeuthen, N., & Kushner, R. F. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989-1002. https://doi.org/10.1056/NEJMoa2032183

This article is for educational purposes only and should not be considered medical advice. Consult with healthcare providers about whether lab monitoring is appropriate for your individual health needs and circumstances while taking GLP-1 medications.