(opens in a new tabThe arrival of GLP-1 receptor agonists has fundamentally changed obesity management. Only a few years ago, sustainable weight loss of 15–20% was rarely achievable without bariatric surgery. Today, medicines such as semaglutide and tirzepatide are helping thousands of UK patients lose clinically significant amounts of weight while reducing cardiovascular risk and improving metabolic health. Last month marked another milestone with the approval of the UK’s first oral GLP-1 treatment for weight management, further expanding access to these medicines. At the same time, the MHRA has strengthened safety advice around GLP-1 therapies, reminding healthcare professionals that while these medicines are highly effective, careful clinical monitoring remains essential.
For clinicians, this raises an important question.
Are we paying enough attention to what happens inside the body while patients are losing weight?
Weight loss isn’t the whole story. Patients often focus entirely on the number displayed on the scales, whereas clinicians know that successful treatment is much broader.
Patients may experience:
- reduced calorie intake
- reduced protein intake
- dehydration
- gastrointestinal symptoms
- changing lipid metabolism
- altered glycaemic control
- nutritional deficiencies
- loss of lean muscle mass alongside fat mass.
Most patients progress extremely well. However, identifying the smaller proportion who require intervention is where pathology becomes valuable. Blood testing cannot tell us everything—but it provides objective data that supports better clinical decisions.
Blood tests should answer clinical questions
Testing should never become a routine “wellness panel” performed without purpose. Instead, every investigation should help answer a specific clinical question.
Interpreting results in context
Perhaps the greatest danger is over-interpreting isolated results. A mildly abnormal liver enzyme in an otherwise well patient may simply require repeat testing. Similarly, a falling HbA1c should be interpreted alongside medication changes, dietary intake and body composition.
Laboratory medicine is most powerful when combined with:
- clinical examination
- medication review
- nutritional assessment
- symptom history
- lifestyle discussion.
This multidisciplinary approach is becoming increasingly important as more patients receive obesity pharmacotherapy across primary care and private practice.
Recent MHRA reminders reinforce the need for vigilance
The MHRA recently strengthened warnings regarding the uncommon but potentially serious risk of acute pancreatitis associated with GLP-1 receptor agonists. Patients should be advised to seek urgent medical attention if they experience severe persistent abdominal pain, particularly if accompanied by nausea or vomiting. Importantly, this does not mean routine blood testing for pancreatitis in asymptomatic patients. Instead, it highlights the importance of appropriate clinical assessment and investigation when symptoms arise.
Nutrition professionals have an increasingly important role
Dietitians and nutritionists often spend more time discussing eating behaviours than prescribing clinicians. This creates opportunities to identify patients whose nutritional intake may no longer meet physiological needs.
Questions around:
- protein intake
- hydration
- fibre
- micronutrient intake
- resistance exercise
- recovery
have become central to successful GLP-1 care.
Where concerns arise, targeted pathology can complement nutritional assessment and help guide appropriate intervention.
Practical blood tests that may be considered
Testing should always be individualised, but depending on clinical circumstances, clinicians may consider:
- HbA1c
- Full Blood Count
- Ferritin (where indicated)
- Vitamin B12
- Folate
- Vitamin D (where clinically appropriate)
- Liver Function Tests
- Renal Function Tests
- Lipid Profile
- High-Sensitivity C-Reactive Protein
VHL has a simple to order Weight Loss Profile Plus (VHLWLP) which looks at all of these markers, plus many more which represents commonly used pathology tests that may assist clinical decision-making when supported by appropriate history and examination.
The future of obesity management is integrated care
GLP-1 medicines represent one of the biggest advances in obesity medicine for decades. Their success, however, should not encourage a “prescribe and forget” approach.
The greatest outcomes will come from combining:
- appropriate prescribing
- nutritional support
- physical activity
- behaviour change
- regular clinical review
- evidence-led laboratory testing where clinically indicated.
Laboratories therefore have an increasingly important role—not in promoting unnecessary testing, but in providing clinicians with reliable data that supports better patient care.
As obesity medicine continues to evolve, pathology will remain one of the most valuable tools for understanding what successful weight loss really looks like beneath the surface.