What Blood Work Should You Track on GLP-1s and Peptides?

On a GLP-1 such as semaglutide or tirzepatide, hs-CRP (an inflammation marker), fasting insulin and HbA1c are the labs most likely to show the treatment working, sometimes before the scale does. ApoB and Lp(a) set your heart-risk baseline. Nutrient and kidney checks catch the problems that long-term use can bring. Test before you start, so every later result has a starting point to compare against.

Which blood tests show a GLP-1 is working besides the scale?

hs-CRP is the clearest one. In three 68-week semaglutide trials, semaglutide 2.4 mg lowered CRP by 44%, 39% and 48% more than placebo.

In those trials, the drop in CRP moved together with drops in weight, waist size, fasting glucose, fasting insulin and HOMA-IR. HOMA-IR is an insulin resistance score worked out from your fasting glucose and fasting insulin. The links were weak to moderate, and the strongest was with weight loss.

CRP-based inflammation markers can still improve when the scale barely moves. A six-month real-world study followed 97 adults (80% women, average age 41) on semaglutide, liraglutide or tirzepatide. Their CRP-to-albumin ratio, an inflammation marker built on CRP, fell 35%. The drop wasn't tied to how much weight they lost, and people who lost less than 5% still saw it fall. This study was a conference abstract.

Tirzepatide has its own evidence in the Zepbound prescribing information. In both of its sleep apnea trials, people on the drug had a bigger drop in hs-CRP than people on placebo.

To read your own number, the semaglutide trials used the standard heart-risk cutoffs. Under 1 mg/L is low, 1 to 3 mg/L is intermediate and above 3 mg/L is high. More people on semaglutide than on placebo moved down a category, although the trials only described this result and did not test it statistically.

If you hit a stall, ask your clinical team to compare these numbers to your baseline. A falling hs-CRP or fasting insulin tells you something the scale can't.

Do you need ApoB and Lp(a) if your cholesterol is normal?

ApoB counts the cholesterol-carrying particles that can build plaque in your arteries, not only the cholesterol inside them. Quest notes that some people with normal LDL still have a high ApoB or Lp(a).

Lp(a) is 80 to 90% inherited, and levels usually stay stable over your lifetime, so you usually only need to test it once.

Treat ApoB and Lp(a) as your heart-risk starting point. They are not a running score for your GLP-1. The studies here don't show how much GLP-1s move ApoB, so don't expect it to track your progress the way hs-CRP does.

Women also have heart risks that standard calculators can miss. A 2018 National Lipid Association review says smoking, PCOS, pregnancy complications, autoimmune disease and past radiation for breast cancer should raise a woman's estimated risk. It notes that preeclampsia is linked to twice the risk of dying from heart disease, and that one study found gestational diabetes raised heart attack risk by 92%. It also lists a high hs-CRP as a factor that raises heart risk. If any of these fit you, tell your clinical team.

What else should you test when you stay on a GLP-1 for years?

Check your nutrients, because eating less can leave you short. A 2026 review found signs of low iron, vitamin B12, vitamin D, calcium, magnesium, potassium and zinc in people on GLP-1s and tirzepatide. It recommends targeted lab testing for people at higher risk.

If you have ongoing vomiting or diarrhea, or you can't keep fluids down, you also need your kidney function and electrolytes such as potassium checked. The prescribing information for semaglutide and tirzepatide advises kidney monitoring when stomach side effects could leave you low on fluids, especially when you start or move up a dose.

Keep checking HbA1c even after it settles. One 65-year-old woman who has been on tirzepatide for more than three years wrote: "Problem now is that exact same behavior (logging food & exercise) is resulting in slowly increasing AIC."

You can skip a routine calcitonin test or thyroid ultrasound. The tirzepatide label says routine checks are of uncertain value for catching medullary thyroid cancer (MTC) early. The important step is telling your clinical team about any personal or family history of MTC or MEN 2, because the drug is not for you if you have either.

Normal labs don't overrule how you feel. One woman who stopped Zepbound after two ER visits wrote: "All my labs look good. Gallbladder and pancreas look good." She still felt too sick to keep going, and her advice was: "Listen to your body while it whispers, before it starts to yell."

Do growth hormone peptides need different blood work?

Yes. The marker researchers watch is IGF-1, the hormone your body makes in response to growth hormone. In a 12-month trial of tesamorelin, a growth-hormone-releasing peptide, the participants were adults with obesity and reduced growth hormone. Their IGF-1 rose from 30% to 49% of the upper limit for their age, while the placebo group went from 34% to 33%. Three people had IGF-1 levels high enough that they needed a lower dose, and two people stopped the drug even after their dose was adjusted.

Researchers also watched blood sugar, because growth hormone given directly is known to worsen insulin resistance. Compared with placebo, tesamorelin did not raise fasting glucose, 2-hour glucose or HbA1c.

The same trial found less fat around the organs, lower triglycerides and lower CRP on tesamorelin. These are the same inflammation and metabolic markers worth tracking on a GLP-1.

These results apply to tesamorelin only. Sermorelin, ipamorelin and CJC-1295 work on the same growth hormone system but haven't been studied the same way, so ask your clinical team whether IGF-1 and glucose belong on your panel. Our clinical team can prescribe these peptides if they fit your goal.

How much does each blood test cost without insurance?

These are the lowest all-in prices for each test bought on its own through Quest or Labcorp direct-access ordering.

Fasting insulin isn't on this price list.

A bundle can cost more than the separate tests. Quest's Advanced Heart Health panel costs $215 plus a $6 physician service fee. It includes hs-CRP, ApoB, Lp(a), lipids and one extra test, Lp-PLA2. Quest accepts HSA and FSA payment and does not bill insurance. At the lowest prices above, hs-CRP, ApoB, Lp(a) and a lipid panel bought separately come to $80.

Here is the order to follow. Get your baseline before you start. Recheck the "is it working" markers once you're settled on a dose. Add nutrient tests if you're eating much less. In the real-world study, inflammation and metabolic markers had improved by the six-month check.

Take the quiz to see which plan fits your goal. Bring your baseline labs so your clinical team can show you what's changing, even in the weeks when the scale won't.