Ozempic and Wegovy Blood Test Monitoring

Over 100,000 people in the UK are now prescribed semaglutide — sold as Ozempic for type 2 diabetes and Wegovy for weight management. Thousands more are buying it through private clinics and online pharmacies. Yet many users aren't getting the regular blood monitoring that NICE, the BNF, and prescribing guidelines recommend.

Semaglutide is effective. Clinical trials showed average weight loss of 15% of body weight over 68 weeks. But it's not without risks, and some of those risks are only detectable through blood tests. Whether you're prescribed semaglutide by the NHS or buying it privately, here's what you should be monitoring — and when.

Important: This article is for information only. It is not medical advice. Always consult your prescribing doctor about monitoring while taking any medication.

Why Blood Monitoring Matters on Semaglutide

GLP-1 receptor agonists like semaglutide affect multiple organ systems beyond appetite and blood sugar. They alter how your liver metabolises fat, change kidney function through fluid shifts, and in rare cases cause pancreatitis or gallbladder problems. Rapid weight loss itself depletes vitamins and minerals, stresses the liver, and can unmask previously hidden deficiencies.

Without regular blood tests, you won't know about these problems until symptoms appear — and by then, damage may already be done.

Liver Function: ALT, AST, GGT, ALP, Bilirubin

Semaglutide is processed through the liver, and GLP-1 agonists as a class have been associated with changes in liver enzymes. In most people, these changes are positive — semaglutide appears to reduce liver fat and improve non-alcoholic fatty liver disease (NAFLD). But in a small number of users, liver enzymes rise significantly.

Key markers:

• ALT (alanine aminotransferase) — the most liver-specific enzyme. Elevated ALT above 45 IU/L in men or 34 IU/L in women suggests liver cell damage.
• AST (aspartate aminotransferase) — rises alongside ALT in liver injury, but also found in muscle and heart tissue.
• GGT (gamma-glutamyl transferase) — sensitive to bile duct obstruction and alcohol use. Also rises with gallbladder issues, which are more common on GLP-1 drugs.
• ALP (alkaline phosphatase) — elevated in bile duct obstruction, relevant because semaglutide increases gallstone risk.
• Bilirubin — rises when the liver is struggling to process waste or when bile flow is obstructed.

Gallstone formation is a known risk of rapid weight loss. NICE guidelines note that GLP-1 agonists carry an increased risk of cholelithiasis (gallstones) and cholecystitis (gallbladder inflammation). Monitoring GGT and ALP can catch these problems early.

Kidney Function: Creatinine, eGFR, Urea

Semaglutide reduces appetite and thirst, and many users report drinking less water as a result. Combined with nausea and occasional vomiting — the most common side effects — this creates a real risk of dehydration, which stresses the kidneys.

The BNF advises monitoring renal function in patients taking GLP-1 agonists, particularly if they experience gastrointestinal side effects. Key markers:

• Creatinine — a waste product filtered by the kidneys. Rising creatinine suggests declining kidney function.
• eGFR (estimated glomerular filtration rate) — calculated from creatinine, age, and sex. Below 60 mL/min indicates moderate kidney impairment.
• Urea — another waste product that rises with dehydration or kidney stress.

People with existing kidney problems should be particularly vigilant. Even those with healthy kidneys should check at least every 6 months while on semaglutide.

Thyroid Function: TSH and FT4

GLP-1 receptor agonists carry a black box warning in the US (and a noted precaution in UK prescribing information) regarding medullary thyroid carcinoma (MTC). This was observed in rodent studies at very high doses. While no causal link has been established in humans, the precaution exists for good reason — and thyroid monitoring is prudent.

TSH and Free T4 should be checked at baseline and periodically while on treatment. A rising TSH or changes in FT4 warrant further investigation. Anyone with a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2 (MEN 2) should not take semaglutide.

HbA1c: Tracking Progress

If you're taking Ozempic for type 2 diabetes, HbA1c is the primary measure of whether the drug is working. The target for most people with type 2 diabetes is below 48 mmol/mol (6.5%), though your doctor may set a different target based on your individual circumstances.

Even if you're taking Wegovy for weight loss without diabetes, HbA1c is worth monitoring. Semaglutide improves insulin sensitivity, and tracking HbA1c shows you the metabolic benefit beyond the scales.

Pancreatitis Screening

Pancreatitis — inflammation of the pancreas — is a rare but serious side effect of all GLP-1 agonists. Symptoms include severe abdominal pain radiating to the back, nausea, and vomiting. Lipase and amylase are the blood markers for pancreatitis. While routine screening for these enzymes isn't standard, having a baseline measurement before starting treatment allows your doctor to compare if symptoms develop.

Nutritional Markers: The Hidden Cost of Rapid Weight Loss

Rapid weight loss — even when medically supervised — depletes the body's stores of vitamins and minerals. Many semaglutide users eat significantly less than before, which means less nutritional intake. Common deficiencies on GLP-1 therapy include:

• Vitamin D — already low in most UK adults; calorie restriction makes it worse
• B12 — particularly at risk if you're also taking metformin, which impairs B12 absorption
• Ferritin and iron — reduced food intake means less dietary iron, especially if you're eating less red meat
• Folate — requires consistent dietary intake from leafy greens, which many people skip

A full blood count alongside these nutritional markers ensures you're not trading weight loss for deficiency-driven fatigue, weakness, or immune problems.

Recommended Testing Schedule

• Before starting semaglutide: baseline blood test covering liver, kidney, thyroid, HbA1c, vitamins, and FBC
• 3 months after starting: repeat all markers to catch early changes
• Every 6 months thereafter: ongoing monitoring while on treatment
• Any time you experience new symptoms: particularly abdominal pain, excessive fatigue, or dark urine

Which Blood Test to Order

The Core Health 45 test (£120) is the best single test for semaglutide monitoring. It covers liver function (ALT, AST, GGT, ALP, bilirubin), kidney function (creatinine, eGFR, urea), thyroid (TSH, FT3, FT4), HbA1c, vitamin D, B12, ferritin, iron studies, folate, and a full blood count — everything listed in this article.

If you want a focused panel for liver and kidney health only, the Liver & Kidney Function test (£81) covers all hepatic and renal markers at a lower price point.

For the most thorough monitoring, the Peak Insights 70 test (£185) adds lipid panel, hormones, and additional metabolic markers to the standard set — useful if you want the complete picture of how semaglutide is affecting your body.

If you're on Ozempic or Wegovy, regular blood monitoring isn't optional — it's essential. Don't wait for your next GP appointment. Order a blood test, get results in 2-3 working days, and stay on top of your health while losing weight safely.