GLP-1 monitoring · Mounjaro, Wegovy, Ozempic
Most people on Mounjaro in the UK get weighed and nothing else. That misses both halves of the story: the markers that should be improving (HbA1c, fasting insulin, liver enzymes, ApoB, blood pressure) and the ones that quietly fall when you eat half as much for a year (ferritin, B12, vitamin D, muscle). A blood test at three months, six months and then every six months shows both, and tells you whether the dose, the diet or the drug needs to change.
Venous draw at 103 UK clinics or at home. Report within 48 hours of the lab receiving your sample. Every result compared against your last one.
Last reviewed 15 September 2026
The short answer
On Mounjaro, test at three months, six months and then every six months: HbA1c and fasting insulin to see the metabolic gain, a full liver and lipid panel including ApoB to see the cardiovascular gain, and ferritin, B12, vitamin D, thyroid and albumin to catch what a long calorie deficit takes away. A kidney panel with cystatin C tells you whether you are losing muscle as well as fat. All of it is in one venous draw, and the value is in the trend, not the single result.
Educational, not a substitute for your prescriber. Dose changes, hypoglycaemia symptoms, severe abdominal pain or persistent vomiting need a clinical conversation, not a blood test.
What to monitor
| Marker | What you want to see | What a warning looks like | Panel |
|---|---|---|---|
| HbA1c | Falling steadily; prediabetes reversing below 42 mmol/mol | Falling too fast if you also take insulin or a sulfonylurea (hypo risk); not moving at all after six months | All panels |
| Fasting insulin, HOMA-IR | Insulin resistance falling; the earliest and clearest proof the drug is working | Still high with weight loss stalled: dose or diet review | Ultimate, Signature |
| ALT, GGT, liver panel | Fatty liver enzymes normalising as weight comes off | A sharp rise, or raised bilirubin and ALP, which can point to gallstones (more common with rapid weight loss) | All panels |
| ApoB, triglycerides, HDL | Triglycerides down, HDL up, ApoB falling: cardiovascular risk genuinely improving | ApoB unchanged despite weight loss, which points to a genetic component worth knowing about | All panels; Lp(a) in Ultimate and Signature |
| hs-CRP | Falling as visceral fat goes | Rising, which can mean gum disease, infection, or a gallbladder problem | All panels |
| Ferritin, iron studies | Stable above 50 | Drifting down month on month; below 30 is deficiency and explains most GLP-1 tiredness | All panels |
| B12, folate | Stable | Falling; slowed stomach emptying reduces absorption, worse on metformin or acid suppressants | All panels |
| Vitamin D | Above 75 nmol/L | Falling with the winter and lower intake; muscle aches and low mood follow | All panels |
| Albumin, creatinine, cystatin C | Albumin stable (protein intake is enough); cystatin C stable (kidneys fine) | Creatinine falling while cystatin C is flat: you are losing muscle, not kidney function. Low albumin: protein too low | Albumin and creatinine in all; cystatin C in Ultimate and Signature |
| Thyroid (TSH, free T4, free T3) | Stable | TSH moving after significant weight loss, especially on levothyroxine: dose needs reviewing | All panels |
| Testosterone (men), oestradiol | Testosterone often rises as weight falls | Falling with rapid weight loss and low protein: a sign of over-restriction | Core hormones in Advanced; complete set in Ultimate and Signature |
Read the individual guides: HbA1c, ApoB, liver, kidney and cystatin C, ferritin, B12, vitamin D, hs-CRP.
When to test
| When | Why | What you are looking for |
|---|---|---|
| Before you start | The baseline everything else is measured against | Your true starting HbA1c, insulin, liver, lipids and nutrients. Before Mounjaro guide. |
| Month 3 | You are usually at or near the maintenance dose and have lost the first 8 to 12 percent | Insulin and HbA1c moving; ferritin, B12 and vitamin D holding; albumin stable; thyroid unchanged |
| Month 6 | The point at which nutrient stores run down if intake has been poor, and when muscle loss shows | Liver enzymes normalising, ApoB falling, hs-CRP falling; any nutrient that has dropped since month 3 needs supplementing now |
| Every 6 months after | Maintenance. Weight often plateaus and the question becomes whether to stay on, reduce or stop | Stable metabolic markers make the case for a lower dose; nutrient trends tell you whether the diet is sustainable |
| 3 months after stopping | Weight regain is common; the blood picture tells you whether the metabolic gains held | Insulin and HbA1c holding is the win; creeping back is the early warning |
Each TrueVitals report compares every marker against your previous result, so month six is read against month three and the baseline, not against a population range. That is what turns a blood test into monitoring.
Which panel
Advanced
74 biomarkers · £269
HbA1c, ApoB and full lipids, liver, kidney, ferritin with iron studies, B12, folate, vitamin D, full thyroid, hs-CRP, albumin and electrolytes. Everything except fasting insulin and cystatin C.
View AdvancedThe GLP-1 monitoring panel
Ultimate
114 biomarkers · £349
Adds fasting insulin and HOMA-IR (the clearest measure of the drug working), cystatin C (muscle loss versus kidney function), Lp(a), complete hormones including testosterone and oestradiol, and tumour markers. The panel built for the trend.
View UltimateHealth plans
2, 3 or 4 tests · from £706
Buy the retests upfront at a lower price per test and book each one when it is due. Built for exactly this: baseline, three months, six months, twelve.
View health plansClinic draw £19. At-home £39. Fast from 10pm the night before; take your Mounjaro as normal. Pay monthly available.
Honest comparison
If you were started on Mounjaro by your GP for type 2 diabetes, you will get an HbA1c every three to six months and probably a kidney and liver check once a year, which is good monitoring for the diabetes and nothing else. If you buy it from an online pharmacy for weight loss, most require a weight, a photo and a questionnaire, and no blood test at all after the first one, if they asked for one then. Neither will notice your ferritin sliding from 60 to 20 over a year, or your creatinine falling because you have lost muscle, or your thyroid dose drifting out of range. Those are the things that make people feel worse on a drug that is working, and a monitoring panel every six months costs less than two months of the prescription.
After your result
Every marker is shown against your previous result and explained in context: what improved because of the drug, what dropped because of the diet, and what to do about each in order.
Ferritin, B12 and vitamin D are corrected with food and supplements. The report gives you the targets and the retest date. Tired on Mounjaro? Why, and what to test.
A steep HbA1c fall on insulin, a liver enzyme spike, a thyroid dose that needs changing or a testosterone that has collapsed all need a prescriber. The report tells you which results to show them and why. What to ask your GP for.
FAQs
A baseline before starting, then at three months, six months and every six months while you remain on it, plus once about three months after stopping. More often is rarely useful because nutrient stores and HbA1c both take around three months to change.
HbA1c and fasting insulin to measure the benefit; liver enzymes and ApoB for the cardiovascular and liver gains; ferritin, B12, vitamin D and albumin to catch what reduced eating takes away; cystatin C alongside creatinine to separate muscle loss from kidney change; and a full thyroid panel if you take levothyroxine or have lost a lot of weight.
No. Take it on its normal day. Fast from 10pm the night before with a morning appointment so that fasting insulin, HbA1c and lipids are accurate.
Not directly, but the pattern is clear: creatinine falling month on month while cystatin C stays flat means muscle mass is dropping rather than kidney function changing, and a low or falling albumin points to protein intake being too low. Both are in the Ultimate panel.
If you have type 2 diabetes, HbA1c and an annual kidney and liver check are standard. Ferritin, B12, vitamin D, fasting insulin, ApoB and cystatin C are not part of routine GLP-1 monitoring on the NHS and are rarely offered by online prescribers.
Yes. Semaglutide works by the same mechanism, so the markers, the risks and the retest points are the same.
Advanced and Ultimate reports are delivered within 48 hours of the laboratory receiving your sample, which is usually the same day as your draw.
One venous draw every six months, 114 biomarkers, and a report that reads each result against your last one. See the drug working, catch what the diet is costing you, and know when to change the dose.
Mounjaro blood tests · Before you start · Tired on Mounjaro · Prediabetes · Find a clinic
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