Wellness . Symptoms guide
Unexplained Weight Loss: When to Test
Quick answer
Unexplained weight loss of more than 5 percent body weight over 6 to 12 months without intentional change warrants assessment. The most common medical causes include hyperthyroidism, undiagnosed diabetes, coeliac disease and inflammatory or infective processes. Bloodwork is the right first step alongside a GP review.
This patient information is being clinically reviewed by our team. The factual content aligns with UK diagnostic frameworks, drawing on NHS primary care pathways, NICE guidelines on coeliac disease and diabetes, and clinical guidance from the British Society of Gastroenterology.
What this might be
- Hyperthyroidism. Raised T3, T4, suppressed TSH.
- Undiagnosed diabetes. Both Type 1 and advanced Type 2 diabetes cause systemic weight loss when a lack of effective insulin prevents cells from absorbing glucose, forcing the body to break down fat and muscle tissue for fuel. Measuring your HbA1c identifies this underlying glycaemic dysfunction immediately.
- Coeliac disease. An autoimmune condition where gluten ingestion causes severe small intestinal inflammation and nutrient malabsorption. Because UK guidelines (NICE) recommend screening for this in all cases of unexplained weight loss, testing for Tissue Transglutaminase (tTG) IgA antibodies alongside Total IgA is a critical baseline requirement, provided you have not already removed gluten from your diet.
- Inflammatory bowel disease. CRP, ESR, full blood count provide signals.
- Malignancy. Less common but routinely considered; bloodwork can help risk-stratify alongside clinical examination and a GP review.
When to seek urgent advice
If any of the following apply, please contact your GP or NHS 111 rather than waiting for private bloodwork.
- Rapid weight loss (more than 5 percent in 1 to 3 months)
- Night sweats
- Persistent abdominal pain or change in bowel habit
- Persistent fever
- Visible blood in your stool or urine (urgent GP or NHS 111 review)
- Vomiting blood, or dark coffee-ground vomit: call 999 or go to A&E immediately, as this can signal a serious internal bleed
Common features that suggest this
- Weight loss not explained by diet or exercise
- Fatigue, anxiety, or palpitations
- Changes in bowel habit
- New persistent abdominal pain
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
Need a marker not in these panels? Build a custom panel and a GMC-registered clinician will design one for you.
Markers your clinician will commonly look at
These are the individual blood markers in the recommended panels above. Click any to read what it measures, its UK reference range, and what high or low values mean.
Testing advice
Fasting recommended for General Wellness. Same-day appointment available. If red flags are present, please contact your GP or urgent care alongside private testing.
Common questions
Can private bloodwork replace a GP review?
Private bloodwork can never replace a face-to-face evaluation by a doctor. Unexplained weight loss is a significant clinical flag that requires a physical examination. However, bloodwork can be done alongside this to help understand the underlying causes.