When Blood Test Results Suggest You Need a Scan

Blood tests measure your body's biochemistry — enzymes, hormones, proteins, cell counts. They're excellent at detecting dysfunction. But they can't show you what a problem looks like structurally. That's where scanning comes in. This guide covers every common blood test abnormality that might lead to an MRI, which scan to get, and the exact biomarker thresholds that doctors use to make referral decisions.

The Blood-Test-to-Scan Decision Map

Detailed Pathways by Blood Test

Liver Enzymes (ALT, AST, GGT, ALP)

Raised liver enzymes are one of the most common triggers for imaging. See our detailed guide: Elevated Liver Enzymes → Liver MRI

• When to scan: ALT >100 U/L on two tests, or any elevation with symptoms (fatigue, abdominal pain, jaundice)
• Which scan: Liver MRI (£299) for liver parenchyma; MRCP (£299) if bile duct obstruction is suspected

PSA (Prostate-Specific Antigen)

PSA above the age-adjusted normal range on two tests warrants prostate MRI. Full guide: High PSA → Prostate MRI

• When to scan: PSA above age-adjusted normal (e.g., >3.5 for men 50–59) on two tests 6+ weeks apart
• Which scan: Multi-parametric prostate MRI (£449)

Thyroid Function (TSH, Free T4, Free T3)

Thyroid blood tests alone don't usually need imaging. It's when you combine abnormal function with structural symptoms. Full guide: Abnormal Thyroid → Thyroid Scan

• When to scan: Neck lump, swallowing difficulty, or ultrasound showing a suspicious nodule
• Which scan: Thyroid MRI (£249) or Neck MRI (£275)

Kidney Function (Creatinine, eGFR)

Full guide: Abnormal Kidney Function → Kidney MRI

• When to scan: eGFR persistently below 60, unexplained decline, haematuria (blood in urine), or abnormal ultrasound
• Which scan: Kidney MRI (£249)

Cholesterol and Cardiovascular Markers

Full guide: High Cholesterol → Cardiac MRI

• When to scan: Total cholesterol >7.5 mmol/L, or high cholesterol with chest pain/breathlessness/family history of heart disease
• Which scan: Cardiac MRI (£349)

CA-125 (Ovarian Cancer Marker)

Full guide: Elevated CA-125 → Pelvic MRI

• When to scan: CA-125 >35 U/mL, especially in postmenopausal women or with pelvic symptoms
• Which scan: Pelvis MRI (£275)

Iron Studies

Full guide: Iron Deficiency → Further Investigation

• When to scan: Persistent iron deficiency despite supplementation, especially with GI symptoms or in men/postmenopausal women
• Which scan: Small Bowel MRI (£399) or Abdomen MRI (£275)

Hormones (Prolactin, Cortisol, Growth Hormone)

Full guide: Hormonal Imbalances → Pituitary MRI

• When to scan: Prolactin >1000 mU/L, or any significant hormonal abnormality suggesting a pituitary cause
• Which scan: Pituitary MRI (£249)

The Smart Screening Approach

If you're not sure what's going on, start broad and narrow down:

1. Order a Peak 70 blood test (£230) — Covers 70 biomarkers across all major organ systems.
2. Review your results — Identify which markers are outside the normal range.
3. Book a targeted scan — Based on which system shows abnormalities. One scan at £249–£449 is far cheaper than a £1,399 full body MRI if you only need one area checked.

This blood-first approach saves money and gives your radiologist clinical context — they know what the scan is looking for, which improves the quality of the report.

Related Guides

• Blood Test Then Scan: Complete Pathway
• Elevated Liver Enzymes → Liver MRI
• High PSA → Prostate MRI
• High Cholesterol → Cardiac MRI
• MRI Scan Cost by Body Part