Before starting Ozempic, and every few months while you take it, the blood tests that matter most are HbA1c, kidney function (creatinine and eGFR), liver function and a lipid profile, plus vitamin B12 if you also take metformin. Ozempic is semaglutide licensed in the UK for type 2 diabetes; Wegovy is the same medicine licensed for weight management. Your diabetes team's monitoring comes first. A private test adds a full baseline and the extras they may not check.
Ozempic is the most searched name, but it is not the weight-loss brand. Both pens contain semaglutide, a GLP-1 receptor agonist made by Novo Nordisk. What differs is what each is licensed for in the UK, the doses, and who usually prescribes them.
| Ozempic | Wegovy | |
|---|---|---|
| Active medicine | Semaglutide | Semaglutide |
| UK licence | Adults with insufficiently controlled type 2 diabetes, alongside diet and exercise | Weight management in adults with a BMI of 30 or more, or 27 to under 30 with at least one weight-related condition |
| On the NHS | Prescribed by your GP or diabetes team as part of diabetes care | NICE TA875: within a specialist weight management service, for up to 2 years, for people meeting its criteria |
| Main blood marker | HbA1c, measured by your diabetes team | No single target marker; a baseline helps track changes as weight falls |
| Our guide | This page | Wegovy blood test |
If you have been given Ozempic purely for weight loss, that is outside its UK licence. The MHRA has said Ozempic is authorised for type 2 diabetes, not weight loss, and in October 2023 warned that fake Ozempic pens had been found in the UK. Only use pens supplied on a prescription from a registered pharmacy.
Some of these checks come straight from UK guidance or the product information. Others are sensible but not required by any guideline. We say which is which.
| Marker | Why it matters on Ozempic | Basis |
|---|---|---|
| HbA1c | Your average blood sugar over roughly the last two to three months, and the main measure of whether treatment is working. More in our HbA1c guide. | NICE NG28 |
| Kidney function: creatinine, eGFR, urea, sodium, potassium | Stomach side effects can cause dehydration, which the product information says can rarely worsen kidney function. Kidney function also matters for diabetes itself. See kidney function tests. | Ozempic SmPC |
| Cystatin C | A kidney marker much less affected by muscle mass than creatinine, useful when weight and muscle are changing. | Sensible extra |
| Liver function: ALT, AST, GGT, ALP, bilirubin | A baseline for later comparison. Gallstones are listed as a common side effect, and a blocked bile duct can raise ALP and bilirubin. | Ozempic SmPC (gallstones) |
| Lipase and amylase | Raised levels are listed as common on semaglutide, and the product information says raised enzymes alone don't predict pancreatitis. A baseline helps a doctor read a later result; it is not a screening test. | Ozempic SmPC |
| Lipid profile: cholesterol, HDL, LDL, triglycerides, ApoB | Heart risk is the big long-term concern in type 2 diabetes, and lipids often change as weight and diet change. | Sensible baseline |
| Vitamin B12 | If you also take metformin, the MHRA says low B12 affects up to 1 in 10 people and advises considering periodic checks in those at risk. See our B12 guide. | MHRA Drug Safety Update, June 2022 |
| Iron, ferritin, folate | Eating much less can lower intake. Worth checking if you feel unusually tired, lose hair or eat very little. | Sensible extra |
| Vitamin D | No GLP-1 guideline requires it. It is a common UK deficiency and worth checking if your diet has narrowed. | Sensible extra |
| Thyroid: TSH, free T4 | The product information does not ask for routine thyroid blood tests. Thyroid function is still worth knowing if you have symptoms, because an underactive thyroid affects weight, energy and cholesterol. | Where relevant |
| Full blood count | Picks up anaemia, which can also make HbA1c harder to read. | Sensible baseline |
If you take insulin or a sulfonylurea alongside Ozempic, the product information warns of a higher risk of low blood sugar. That is managed with finger-prick glucose checks and dose changes from your prescriber, not with a lab blood test.
| When | Why | What to check |
|---|---|---|
| Before your first dose | Shows where you started, so later changes are easy to read. Also finds anything your prescriber should know first, such as reduced kidney function. | The full list above |
| About 3 months in | HbA1c has had time to reflect the new treatment. A good point to see whether kidney function, liver and lipids have changed. | HbA1c, kidney, liver, lipids |
| Every 6 months once stable | NICE's interval for HbA1c once it is stable on unchanging treatment. Add B12 if you take metformin. | HbA1c, kidney, B12 if relevant |
| After a bad spell of side effects | Persistent vomiting or diarrhoea can dehydrate you. A kidney check shows whether it has affected your kidneys. | Creatinine, eGFR, electrolytes |
| If you feel unusually tired | Low iron, B12 or folate are common, fixable reasons, especially if you are eating much less. Our GLP-1 monitoring guide covers this in more depth. | FBC, ferritin, B12, folate, vitamin D, thyroid |
Starting a weight loss injection rather than Ozempic? See our blood test before Mounjaro guide; the baseline is very similar.
A result is a pattern, not a diagnosis. Take anything abnormal to the clinician who prescribes your Ozempic.
| Result | What it can mean | What to do |
|---|---|---|
| HbA1c falling towards 48 to 53 mmol/mol | Treatment is working. NICE suggests 48, or 53 if you take a medicine linked to low blood sugar. | Keep to your diabetes team's plan. |
| HbA1c not moving after 3 to 6 months | The current dose or plan may need reviewing | Talk to your prescriber. Don't change your dose yourself. |
| eGFR lower than your baseline, creatinine higher | Possible dehydration or a kidney change | Drink normally and repeat. If it stays low, or you have been vomiting, speak to your prescriber. |
| Raised ALP and bilirubin, with pain under the right ribs | Possible gallstone problem | Get medical advice promptly; urgently if you are yellow or have a fever. |
| Raised lipase on a routine test, no symptoms | Common on semaglutide and not, on its own, a sign of pancreatitis | Mention it to your prescriber at your next review. |
| Low B12 | Often linked to metformin, or to eating much less | See your GP or prescriber. Don't start high-dose supplements without advice. |
| Low ferritin or folate | Low intake while eating much less | Discuss diet and treatment with your GP. |
| Abnormal TSH | Thyroid under- or over-activity | See your GP; thyroid problems are common and treatable. |
Three routes, each good for something different. Competitor details were read on their own website in November 2026.
Does well: free, and the results go straight to the people who adjust your treatment. HbA1c and kidney checks are part of routine diabetes care.
Limits: the checks are focused on diabetes control and may not include B12, iron, vitamin D, thyroid or ApoB unless there is a reason.
Choose it if: you are on Ozempic for type 2 diabetes and mainly need HbA1c and kidney monitoring.
Does well: a focused, low-cost check built for weight loss injection users. £99 for 34 biomarkers covering HbA1c, kidney, liver, lipids, a full blood count, ferritin, folate and lipase. Venous sample, with a doctor's report included; results estimated in 5 working days from the lab receiving the sample. Collection at a clinic or by a nurse costs extra, or you can arrange the draw yourself.
Limits: its marker list does not include B12, vitamin D or thyroid function.
Choose it if: you want a targeted safety check at the lowest price.
Does well: one baseline that covers everything on this page: HbA1c, glucose and fasting insulin, kidney function with cystatin C, liver, amylase and lipase, full lipids with ApoB and Lp(a), full blood count, iron, B12, folate, vitamin D and thyroid. 140 biomarkers (139 for women), £399 including the blood draw at one of 103 partner clinics, or £29 extra for a home or office visit. Nationwide Pathology, a UKAS-accredited lab, runs the tests; the clinician-reviewed report arrives within 4 working days of the lab receiving your sample, written from your own lifestyle quiz and reading the results together across systems.
Limits: it costs more than a focused GLP-1 check, and it measures total rather than active B12.
Choose it if: you want a full starting point, or you feel unwell and want the broader picture. Our full comparison of weight loss injection tests goes marker by marker.
Sources: Ozempic SmPC · Wegovy SmPC · EMA, Ozempic · NICE NG28 · NICE TA875 · MHRA, metformin and B12 · MHRA, fake pens · Medichecks GLP-1 test
A useful baseline is HbA1c, kidney function (creatinine, eGFR and electrolytes), liver function, a lipid profile and a full blood count, plus vitamin B12 if you take metformin. Iron, folate, vitamin D and thyroid function are sensible extras if you expect to eat much less or feel tired. Your prescriber decides what is clinically required; a baseline lets you read later results against your own starting point.
They contain the same medicine, semaglutide, but are licensed for different things. In the UK, Ozempic is licensed for adults with type 2 diabetes that is not well controlled, alongside diet and exercise. Wegovy is licensed for weight management in adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition. The MHRA has said Ozempic is authorised for type 2 diabetes, not for weight loss.
NICE guideline NG28 says adults with type 2 diabetes should have HbA1c measured every 3 to 6 months until it is stable on unchanging treatment, then every 6 months. Your diabetes team sets your own schedule and target; NICE suggests aiming for 48 mmol/mol, or 53 mmol/mol if you take a medicine linked to low blood sugar.
Not routinely. The UK product information lists raised lipase and amylase as common on semaglutide, and says raised pancreatic enzymes alone do not predict acute pancreatitis. A baseline can help a doctor interpret a later result, but the warning sign that matters is severe, persistent stomach pain, which needs urgent medical help rather than a blood test you book yourself.
The bigger B12 issue is usually metformin, which many people on Ozempic also take. The MHRA says reduced vitamin B12 is a common side effect of metformin, affecting up to 1 in 10 people, and advises testing if deficiency is suspected and considering periodic checks in people with risk factors. Eating much less can also lower B12, iron and folate intake.
It can, indirectly. The UK product information warns that nausea, vomiting and diarrhoea can cause dehydration, which in rare cases can worsen kidney function. That is why creatinine and eGFR are worth checking at baseline and again if you have had a spell of stomach upset. Drink enough fluid and tell your prescriber about persistent vomiting or diarrhoea.
It depends on what you need. For a focused, low-cost check, Medichecks' Weight Loss Injection (GLP-1) Monitoring test was £99 for 34 biomarkers when we checked in November 2026, plus a collection fee unless you arrange the draw yourself. For a broader baseline that adds B12, vitamin D, thyroid, ApoB and cystatin C, TrueVitals Ultimate is 140 biomarkers for £399 including the clinic draw. Neither replaces your diabetes team's checks.
Ultimate: 140 biomarkers, £399 including your blood draw. HbA1c, kidney function with cystatin C, liver, lipids with ApoB, B12, iron, vitamin D and thyroid, in a clinician-reviewed report within 4 working days. Klarna or Clearpay at checkout.
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