Before starting Mounjaro (tirzepatide), a structured set of blood tests serves three purposes: checking for contraindications that would make the medication unsafe, establishing a baseline metabolic picture to track your progress against, and identifying any underlying issues — thyroid dysfunction, iron deficiency, or blood sugar problems — that might affect your treatment or results.
Essential Baseline Blood Tests
| Test | Why It Matters Before Mounjaro |
|---|---|
| HbA1c | Establishes baseline blood glucose control. Mounjaro has significant glucose-lowering effects — your starting HbA1c determines whether you're at risk of hypoglycaemia (especially important if on other diabetes medications) and gives a baseline to track metabolic improvement. |
| Fasting glucose | Provides a direct snapshot of current glucose, complementing HbA1c. Identifies undiagnosed type 2 diabetes or impaired fasting glucose (pre-diabetes). |
| Lipid profile | Baseline cholesterol (total, LDL, HDL, triglycerides). Tirzepatide improves lipid profiles — a before/after comparison at 3–6 months shows the full metabolic benefit of treatment. |
| Liver function tests (LFTs) | Non-alcoholic fatty liver disease (NAFLD) is common in people with obesity and often asymptomatic. Knowing your baseline LFTs is important — tirzepatide improves liver function, and raised enzymes pre-treatment require monitoring. |
| Kidney function (eGFR, creatinine) | GLP-1 receptor agonists are generally renoprotective, but significant renal impairment affects how you may tolerate the medication and whether dosing needs adjustment. |
| Thyroid function (TSH) | Thyroid dysfunction causes weight gain and metabolic slowdown — commonly missed. If your thyroid is underactive, treating it is essential alongside weight loss medication. Also: tirzepatide carries a theoretical risk related to thyroid C-cell tumours — relevant if you have a personal or family history of medullary thyroid carcinoma (a contraindication). |
| Full blood count (FBC) | Baseline haematology. Anaemia — particularly iron deficiency — is common and causes fatigue that may be confused with medication side effects. |
| Ferritin | Iron stores are often low before weight loss starts and can fall further as appetite decreases. Identifying iron deficiency early prevents significant fatigue during treatment. |
| Amylase / lipase | Pancreatitis is a rare but documented adverse effect of GLP-1 receptor agonists. Baseline pancreatic enzyme levels are useful if you develop abdominal pain during treatment, and a history of pancreatitis is an important contraindication to consider. |
| Vitamin B12 | Appetite suppression reduces food intake — B12 from animal sources may decline. A baseline level guides whether supplementation is needed. |
What the Blood Tests Tell You Beyond Safety
A pre-treatment metabolic panel gives you a baseline that makes your progress visible. Three months into treatment, repeat HbA1c, lipids, and liver function often show dramatic improvements even before significant weight loss. Understanding your starting position makes the benefits of treatment tangible — and motivating — in a way that weight alone doesn't capture.
Can I Get These Tests Done Privately?
Yes. Lambert Medical Practice offers a pre-weight loss blood panel that covers all the above tests from a single draw. Results are reviewed by Dr Raj Dhillon and discussed at a follow-up consultation before any weight loss prescription is issued. We don't prescribe Mounjaro without a clinical assessment and review of results.
Pre-Mounjaro Blood Tests in Surbiton
Comprehensive metabolic baseline from a single blood draw. Book your private consultation at Lambert Medical Practice.
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