Blood tests: ruling out reversible causes

Why blood tests are part of the work-up

Several treatable conditions cause cognitive symptoms that can mimic or worsen dementia. NICE NG97 recommends a standard blood panel for every person undergoing dementia assessment. The aim is twofold: rule out treatable contributors, and capture vascular risk factors that influence the trajectory of any underlying dementia.

The standard panel

Full blood count

Looks for anaemia (low haemoglobin), which can reduce cognitive performance, and for low or raised white cell counts (suggesting infection or other concerns).

Renal function and electrolytes

Urea, creatinine, sodium, potassium and estimated glomerular filtration rate (eGFR). Kidney impairment affects medication choices. Sodium disturbance is a classic reversible cause of confusion.

Liver function tests

ALT, AST, alkaline phosphatase, bilirubin, GGT. Raised liver enzymes can suggest alcohol-related disease or other liver problems contributing to cognitive symptoms.

Bone profile

Calcium and corrected calcium. Both high and low calcium can affect cognition.

Thyroid function

Thyroid stimulating hormone (TSH) and free T4. Hypothyroidism is a classic reversible cause of cognitive impairment in older adults. Treatment usually restores function.

Vitamin B12 and folate

B12 deficiency causes a reversible cognitive impairment that can mimic dementia. Folate deficiency similarly affects cognition. Both are treated with supplements or injections.

Vitamin D

Insufficiency is common in the UK. Treatment with daily Vitamin D 10 micrograms is recommended for most people; higher doses for confirmed deficiency. The link with cognitive function is modest but real.

Lipid profile

Total cholesterol, LDL, HDL, triglycerides, total cholesterol to HDL ratio. Used for vascular risk assessment.

HbA1c and random glucose

Glycated haemoglobin assesses average blood glucose over 8 to 12 weeks. Used to diagnose diabetes and assess control. Diabetes is an important contributor to dementia risk.

C-reactive protein and ESR

Inflammatory markers. Raised levels suggest infection, autoimmune or other inflammatory processes contributing to symptoms.

Additional tests sometimes added

• Syphilis serology (rarely a cause of cognitive impairment but routinely tested);
• HIV testing in selected cases;
• Coeliac screening if anaemia or B12 deficiency is unexplained;
• Autoimmune screen if there are suggestive features;
• Toxicology screen in selected cases.

What if a result is abnormal?

The clinician interprets each result in the clinical context. Common scenarios:

• Low Vitamin B12: usually treated with intramuscular injections or high-dose oral supplements. Cognitive symptoms often improve over weeks to months.
• Hypothyroidism: treated with Levothyroxine; cognitive symptoms usually improve when TSH is in target range.
• Raised glucose or HbA1c: confirms diabetes or pre-diabetes; lifestyle and medication addressed.
• Raised cholesterol: vascular risk modification, often with a statin under NICE CG181.
• Anaemia: investigation of cause and treatment.

Where a reversible contributor is identified, treatment first; then re-assess cognitive function in 3 to 6 months.

What blood tests do not show

Blood tests cannot diagnose Alzheimer's Disease, Vascular Dementia or other dementias directly. They identify contributors and exclude alternative causes. Emerging blood-based biomarkers (plasma amyloid, plasma tau) may change this in coming years; they are not yet in routine UK clinical use.

What to bring

Fasting blood samples (for accurate lipid and glucose results) are usually requested. Otherwise no specific preparation is required.