Semaglutide Blood Work: The Labs Before and During Treatment

These are the markers we want before treatment starts. We do not publish target values or ranges on this page; what counts as a concern depends on the person, and the reference range printed on a lab report is only part of it.

HbA1c

HbA1c reflects average blood sugar over the past two to three months. It is how prediabetes and type 2 diabetes are usually picked up, and it matters here in two ways. If it shows diabetes, the plan changes: the Wegovy label warns that taking a GLP-1 alongside insulin or a sulfonylurea raises the risk of low blood sugar, and it flags diabetic eye disease for monitoring in people with type 2 diabetes. And because it moves slowly, it is one of the clearest markers of whether treatment is changing metabolic health.

Fasting glucose and fasting insulin

Fasting glucose is a snapshot of blood sugar on the morning of the draw. Fasting insulin shows how hard the pancreas is working to hold it there. Together they give HOMA-IR, an estimate of insulin resistance. Someone with normal glucose but high insulin is compensating, and that can show up before HbA1c moves at all.

Lipids

A cholesterol panel gives LDL, HDL and triglycerides, which together describe cardiovascular risk, and a baseline shows whether treatment is moving them. Some patients also benefit from ApoB, which counts the particles that drive plaque; whether it is worth adding is a judgment for the clinician.

Kidney function

Creatinine and the estimated filtration rate (eGFR) show how well the kidneys are filtering. The Wegovy label reports acute kidney injury after semaglutide, mostly in people who became dehydrated from nausea, vomiting or diarrhea, and it tells clinicians to monitor kidney function in patients with those side effects. A baseline value is what makes a later reading interpretable.

Liver enzymes

ALT and AST are the liver enzymes most often raised by fatty liver, which is common in people carrying extra weight. A raised value is a reason to look further, not a reason to start the drug; our page on semaglutide and fatty liver covers that. Liver tests are also part of working up gallbladder symptoms, which the Wegovy label lists as more common on the drug than on placebo.

Thyroid

TSH shows how well the thyroid is working. An underactive thyroid slows metabolism and causes fatigue, weight gain and hair thinning, so it is worth ruling out before blaming everything on weight. TSH is a test of thyroid function. It is not a cancer screen. The Wegovy label carries a boxed warning about thyroid C-cell tumors seen in rodents, and it says routine calcitonin testing or thyroid ultrasound is of uncertain value for picking up that cancer early. That warning is handled through history (a personal or family history of medullary thyroid cancer or MEN 2 rules the drug out), not through a blood test. If you take levothyroxine and are considering the oral form, see oral semaglutide and thyroid medication.

Lipase, where indicated

Lipase is the test used to look for pancreatitis. It is not a routine screen on semaglutide, and the label explains why: in Wegovy's weight-reduction trials, lipase rose from baseline on average with no matching rise on placebo, and the label says the meaning of that rise is unknown without symptoms of pancreatitis. A raised number on its own would cause more alarm than it resolves. Lipase is checked where there is a reason: a past history of pancreatitis, or symptoms such as severe abdominal pain spreading to the back, which the label says should prompt stopping the drug and seeking care.

There is no single published schedule for this, and we do not pretend otherwise. What we do is built on how quickly each marker can change.

Before starting. The full baseline above.

A few months in. HbA1c reflects about three months of blood sugar, so rechecking it sooner tells you little. A recheck once you have been on treatment for a few months shows whether the metabolic markers are moving, and whether kidney and liver values have stayed steady.

Once things are steady. Longer gaps between panels, set by your clinician according to what the baseline showed. Someone with prediabetes or a raised liver enzyme is rechecked more often than someone whose panel was clean.

Any time something changes. Persistent vomiting or diarrhea, signs of dehydration, severe abdominal pain, or yellowing of the skin are reasons to contact your clinician the same day, not reasons to wait for the next scheduled draw. Our GLP-1 side effects FAQ lists the warning signs.

Labs do not predict how much weight a person will lose, and a clean panel does not mean treatment is pointless. They also miss what happens between draws. Weight, waist and body composition fill part of that gap; resting heart rate, which the Wegovy label asks clinicians to monitor, fills another. For people who want to see blood sugar day to day, a continuous glucose monitor on a GLP-1 shows how meals and the medication interact in a way a fasting draw cannot.

The Comprehensive Lab Panel is $199, and our lab testing page explains how the draw works. What lab work costs elsewhere, and how it compares, is on the lab testing cost page.