GLP-1 Blood Work: Labs Before and During Semaglutide or Tirzepatide

If you have type 2 diabetes

The ADA advises checking A1c at least twice a year when you meet your goals, and more often, such as every 3 months, after a treatment change or when you are not at goal^[1]. Starting a GLP-1 is a treatment change, so most people get an A1c about 3 months in. A goal under 7% fits many adults, but your goal may be higher or lower based on your health and hypoglycemia risk^[1].

Kidney checks are also on a set schedule. People with type 2 diabetes should have eGFR and a urine albumin test at least once a year, and one to four times a year if they already have kidney disease^[9]. A yearly lipid panel is reasonable for adults with diabetes who are not on a statin^[8].

Learn more about these markers in our pages on type 2 diabetes labs and what a high A1c means.

If you are taking it for weight without diabetes

If you use Wegovy or Zepbound for weight and do not have diabetes, there is no guideline lab schedule written just for you. The big trials, STEP 1 and SURMOUNT-1, enrolled only people without diabetes^[10][11], and both saw better cardiometabolic risk factors on the drug. Repeat labs show whether that is happening for you.

A practical pattern many prescribers use: a baseline panel, a recheck once you reach your maintenance dose, then yearly. The ADA advises check-ins at least every 3 months during active weight treatment^[5], and a lab draw often lines up with one of those visits. Extra tests make sense with side effects, such as kidney tests after days of vomiting. If your baseline showed prediabetes or insulin resistance, a repeat A1c shows whether your blood sugar is moving back toward normal.

A1c and fasting glucose

These drugs lower blood sugar, so A1c and fasting glucose usually fall. Because A1c reflects blood sugar over the past few months, an early recheck can understate the full effect. That is one reason the ADA suggests every 3 months after a change rather than every few weeks^[1].

The risk to watch is low blood sugar. On their own, these drugs rarely push glucose too low. The risk rises when they are combined with insulin or a sulfonylurea such as glipizide or glimepiride^[12]. In a Zepbound trial in people with type 2 diabetes, readings under 54 mg/dL happened in 10.3% of people also taking a sulfonylurea, versus 2.1% of those who were not^[3]. The labels also note low blood sugar can occur in people without diabetes^[3].

Will my cholesterol go down on tirzepatide or semaglutide?

Often, yes, especially triglycerides. In SURMOUNT-1, every prespecified cardiometabolic measure improved with tirzepatide^[11], and STEP 1 also reported better cardiometabolic risk factors with semaglutide^[10]. Triglycerides tend to respond most to weight loss and lower blood sugar. LDL often moves less.

A lipid panel before you start and about a year in shows your own change. If you start or change a statin, the ADA advises a lipid panel 4–12 weeks later^[8]. If LDL is your main concern, an apolipoprotein B test or our high cholesterol guide can add detail.

Does Ozempic affect liver enzymes?

For most people, ALT and AST come down as liver fat goes down. Fatty liver, now called MASLD, is common with obesity and type 2 diabetes, and mildly raised ALT is often the first clue. Wegovy is now FDA approved to treat MASH, the inflamed form of fatty liver, with moderate to advanced scarring^[2]. In the ESSENCE trial, liver inflammation resolved without worse scarring in 62.9% of people on semaglutide 2.4 mg versus 34.3% on placebo^[13].

Normal liver enzymes do not rule out liver scarring. That is why the ADA recommends a FIB-4 score for adults with type 2 diabetes or prediabetes, built from age, ALT, AST and platelets^[6]. A FIB-4 of 1.3 or higher should lead to a liver stiffness scan^[6]. A CMP plus a CBC gives everything needed to calculate it.

A sudden ALT or AST jump on treatment is different. It can come with gallstones, which are more common on these drugs^[2]. See our page on labs for fatty liver for more.

Does semaglutide affect kidney function?

Over the long run, semaglutide appears to protect the kidneys in people with type 2 diabetes and kidney disease. In the FLOW trial, semaglutide 1 mg cut the risk of major kidney events by 24% over a median of 3.4 years, and slowed the yearly eGFR decline by 1.16 units^[14]. Ozempic now carries an FDA indication to lower the risk of eGFR decline and kidney failure in that group^[12].

The short-term risk is dehydration. All four labels report acute kidney injury, sometimes needing dialysis, mostly in people who had nausea, vomiting or diarrhea^[2][3]. The labels ask prescribers to monitor kidney function in these patients, especially when starting or raising the dose^[12][4]. A CMP shows creatinine and eGFR. A cystatin C test can help when muscle loss makes creatinine harder to read.

CBC, vitamins and nutrition during fast weight loss

Eating much less can mean taking in fewer vitamins, minerals and protein. The ADA advises that people losing weight on purpose be counseled and monitored for adequate nutrition, with special attention to protein and micronutrients^[5]. In a large U.S. study of people prescribed GLP-1 drugs, nearly 13% had a nutritional deficiency diagnosed by 6 months and over 22% by 12 months, most often vitamin D^[5].

The ADA says people with weight loss over 20%, or faster than 4% per month, should be screened for micronutrient deficiencies^[5]. There is no set schedule. Nutrients of concern include iron, vitamin D and vitamin B12^[5]. Useful tests include vitamin D, vitamin B12, ferritin and a CBC for anemia. If you also take metformin, the ADA lists a B12 check after more than 5 years of use^[6].

Lipase, amylase and pancreatitis

Acute pancreatitis, including rare severe cases, has been seen with GLP-1 drugs. The labels tell clinicians to watch for persistent, severe belly pain that may spread to the back, with or without vomiting^[2]. Separately, the pancreas enzymes lipase and amylase tend to rise a little in people who feel fine. The table shows the mean rises reported in each label.

In a meta-analysis of 17 trials with 14,645 people, tirzepatide raised amylase and lipase more than placebo, yet pancreatitis risk was similar to placebo^[15]. That is why lipase is not a routine screening test on these drugs. It is useful when you have symptoms. In Wegovy's liver trial, lipase above 3 times the upper limit occurred in 4.7% of treated people versus 1.3% on placebo^[2]. If you need it, the lipase test or the pancreatic enzymes panel covers it.

Gallbladder problems

Gallstones and gallbladder inflammation are more common on these drugs. In Wegovy weight trials, gallstones were reported in 1.6% of adults on the injection versus 0.7% on placebo^[2]. In Zepbound trials, gallbladder inflammation occurred in 0.7% versus 0.2%^[3]. Fast weight loss itself raises the risk^[2].

No routine blood test predicts gallstones. If you have pain in the upper belly, fever, yellow skin or eyes, or clay-colored stools, the label says to tell your provider right away^[3]. They may then order an ultrasound and liver tests such as a hepatic panel.

Do you need a thyroid test or calcitonin before Wegovy?

All four drugs carry a boxed warning because they caused thyroid C-cell tumors in rodents. It is unknown whether they cause these tumors, including medullary thyroid cancer (MTC), in humans^[2][3]. They should not be used by anyone with a personal or family history of MTC or with MEN 2, a genetic syndrome.

The labels do not ask for a calcitonin blood test. They say routine calcitonin monitoring or thyroid ultrasound is of uncertain value for catching MTC early, and may lead to unneeded procedures because the test is not specific and thyroid disease is common^[2][3]. If calcitonin is measured and found high, more evaluation is needed. People with MTC usually have values above 50 ng/L^[2].

What matters most is your family history and your symptoms: a lump in the neck, trouble swallowing, shortness of breath or lasting hoarseness^[2]. A TSH test checks overall thyroid function. It is a reasonable baseline, but it does not screen for C-cell tumors. Our pages on high TSH and hypothyroidism labs explain what it does show.

Eyes and heart rate

Two warnings have no blood test at all. In a 2-year semaglutide trial in people with type 2 diabetes, eye complications occurred in 3% versus 1.8% on placebo, with the larger rise in people who already had diabetic eye disease^[2]. Fast drops in blood sugar can briefly worsen retinopathy, so people with a history of it should keep their eye exams^[3].

Resting heart rate rose by a mean of 1 to 4 beats per minute on Wegovy^[2]. The label asks clinicians to check heart rate at regular visits. Tell your prescriber about a racing heartbeat at rest.