GLP-1 Bloodwork: What the Trials Actually Measured
Every big GLP-1 trial drew blood. HbA1c was the headline in the diabetes trials, cardiometabolic markers came along in the obesity trials, and the safety programs tracked pancreatic enzymes and calcitonin. Here is what moved, by how much, and which of those tests you can order yourself.
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In SURPASS-2 (1,879 adults with type 2 diabetes), HbA1c was the primary endpoint: from 8.28% at baseline it fell 2.01, 2.24 and 2.30 points on tirzepatide 5, 10 and 15 mg versus 1.86 on semaglutide 1 mg over 40 weeks (Frías et al., NEJM 2021).
The obesity trials put weight first and labs second. STEP 1 (semaglutide 2.4 mg, 68 weeks) and SURMOUNT-1 (tirzepatide, 72 weeks) both reported improvements in cardiometabolic risk factors, which include lipids and glucose (Wilding 2021; Jastreboff 2022).
In pooled SCALE trials of liraglutide 3.0 mg, 43.5% of people had lipase at or above the upper limit of normal versus 15.1% on placebo. Levels returned to baseline after stopping, and the authors found no basis for monitoring enzymes except when pancreatitis is suspected (Steinberg 2017).
In rodents, GLP-1 drugs have been associated with higher calcitonin and C-cell tumors. In over 5,000 people on liraglutide or control therapy, calcitonin measured every 3 months for up to 2 years stayed at the low end of normal, with no consistent dose or time effect (Hegedüs 2011).
What the Data Shows
Which Labs Did the GLP-1 Trials Track?
Each row is a lab the published trials reported, what they found, and where the same test can be ordered. Rows built on liraglutide data say so: it is the older drug in the class with the largest dedicated lab analyses.
HealthLabs links are affiliate links. More context: GLP-1s and the thyroid warning · tirzepatide vs semaglutide · retatrutide TRIUMPH-1.
Key Takeaways
- HbA1c is the lab the diabetes trials were built around: in SURPASS-2 it fell 1.86 points on semaglutide 1 mg and 2.01–2.30 points on tirzepatide over 40 weeks.
- The obesity trials (STEP 1, SURMOUNT-1) measured weight first and reported cardiometabolic risk-factor improvements as secondary results.
- On liraglutide, lipase and amylase rise on average, return to baseline after stopping, and elevated levels did not predict pancreatitis (positive predictive value under 1%).
- Calcitonin, the thyroid C-cell marker, showed no consistent drug effect in over 5,000 liraglutide trial participants followed for up to 2 years.
- In people with type 2 diabetes and chronic kidney disease, semaglutide 1 mg slowed the yearly eGFR decline by 1.16 mL/min/1.73 m² (FLOW).
- Retatrutide cut liver fat by 82.4% (relative) at 24 weeks on 12 mg in its phase 2 substudy, and TRIUMPH-2 reported improved glycemic control.
- The pancreatic-enzyme and calcitonin analyses here are liraglutide data; these papers do not show the same numbers for semaglutide, tirzepatide or retatrutide.
- No trial tested whether self-ordered lab checks improve outcomes for someone taking a GLP-1 drug.
- TRIUMPH-1’s primary outcomes were weight, knee-osteoarthritis pain and sleep apnea; its abstract reports no lab endpoints.
- Calcitonin follow-up ran up to 2 years; the authors said longer-term consequences need further study.
- Trial labs come from the manufacturers’ drug under trial conditions; they say nothing about compounded or research-grade vials.
Frequently Asked Questions
What blood tests did the semaglutide and tirzepatide trials track?
The diabetes trials made HbA1c the main lab: in SURPASS-2 it fell 1.86 points on semaglutide 1 mg and up to 2.30 on tirzepatide. The obesity trials, STEP 1 and SURMOUNT-1, reported improved cardiometabolic risk factors. Liraglutide’s safety program tracked lipase, amylase and calcitonin. Which tests suit you is a prescriber question.
Do GLP-1 drugs like Ozempic raise lipase?
The largest dedicated analysis is for liraglutide, an older drug in the same class. Across 5,358 people, lipase rose 31% on average versus placebo, and 43.5% had a level at or above normal limits versus 15.1% on placebo. Levels fell back after stopping, and elevations did not predict pancreatitis.
Does semaglutide or tirzepatide raise calcitonin?
The human data come from liraglutide. In over 5,000 trial participants, calcitonin measured every 3 months for up to 2 years stayed at the low end of normal, with no consistent dose or time effect. The rodent thyroid finding behind the boxed warning did not show up as rising calcitonin.
What did the retatrutide trials measure besides weight?
TRIUMPH-2, in adults with obesity and type 2 diabetes starting at an average HbA1c of 7.71%, reported improved glycemic control. A phase 2 substudy measured liver fat, which fell 82.4% at 24 weeks on 12 mg. TRIUMPH-1’s primary outcomes were weight, knee pain and sleep apnea.
Can I order GLP-1 bloodwork myself?
Yes. Direct-to-consumer lab services such as HealthLabs sell HbA1c, lipid panels, comprehensive metabolic panels, lipase, amylase and liver function tests online, and you get drawn at a local lab. Results are only useful with context, so share them with whoever prescribes your medication.
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This page summarizes which labs published trials measured. It is not a testing schedule; decide on bloodwork with the clinician who prescribes your medication.
Retatrutide is an investigational drug.