Symptom Guide

Memory Loss & Forgetfulness

Name: Memory Loss: Causes, Blood Tests & When to See a Doctor
Creator: Suman Konda
Published: 2026-07-05

Memory loss can be caused by treatable conditions like thyroid disease, B12 deficiency or depression: or may indicate dementia. Blood tests identify the reversible causes first.¹

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

Blood tests for memory loss

Test	Why ordered	Treatable if abnormal?
TSH	Hypothyroidism: cognitive slowing, confusion	Yes: thyroid hormone replacement
Vitamin B12	B12 deficiency dementia: a reversible cause	Yes: B12 injections or supplements
Folate	Folate deficiency: cognitive impairment	Yes: folic acid supplements
Fasting glucose / HbA1c	Diabetes affects brain function	Yes: blood sugar control
FBC	Anaemia: reduces oxygen to the brain	Yes: treat underlying cause
Calcium	Hypercalcaemia causes confusion	Yes: treat calcium disorder
LFT	Hepatic encephalopathy	Yes: treat liver disease
Syphilis serology (RPR/VDRL)	Neurosyphilis: rare but treatable	Yes: antibiotics

When memory loss is more than normal ageing

Warning signs that need urgent assessment

Normal age-related memory changes include occasionally forgetting names or misplacing objects but remembering them later. Concerning features that need prompt evaluation: forgetting recently learned information repeatedly; getting lost in familiar places; difficulty with everyday tasks (managing finances, cooking); personality or behaviour changes; confusion about time, place or people; repeating the same question multiple times in the same conversation.

Dementia: when blood tests are normal

If all blood tests are normal but significant memory impairment persists, the most common diagnoses are Alzheimer's disease (60–70% of dementias), vascular dementia, Lewy body dementia, or frontotemporal dementia. Further investigation may include: cognitive testing (MMSE, MoCA), brain MRI, and in specialist centres, PET scan or cerebrospinal fluid biomarkers (amyloid, tau). Referral to a memory clinic or neurologist is recommended.

Questions to ask your doctor

Have reversible blood test causes been ruled out?
Should I have a formal cognitive assessment?
Do I need a brain MRI?
Should I see a memory clinic or neurologist?

Frequently Asked Questions

Is memory loss always a sign of dementia?

No. Occasional forgetfulness is normal, and many reversible conditions, thyroid problems, B12 deficiency, depression, poor sleep, and stress, cause memory issues that improve once treated.

What blood tests are done for memory problems?

Doctors typically check thyroid function, vitamin B12 and folate, calcium, glucose, and a full blood count to rule out treatable causes before considering cognitive assessment.

When should memory loss prompt a doctor's visit?

See a doctor if memory problems are progressive, interfere with daily life, or are noticed by family: early assessment identifies treatable causes and enables planning if needed.

References

Sources cited on this page. PubMed links open the original abstract.

Petersen RC, Lopez O, Armstrong MJ, et al. Practice guideline update summary: Mild cognitive impairment. Neurology. 2018;90(3):126–135. PMID 29282327 · doi:10.1212/WNL.0000000000004826

Distinguishing normal ageing from early dementia

Some degree of cognitive slowing is part of normal ageing: processing speed decreases, multitasking becomes harder, and occasional "tip of the tongue" experiences increase. This is distinct from dementia. Key distinguishing features of early dementia:

Progression: Normal ageing memory lapses are stable over years; dementia symptoms progress measurably over months.
Impact on function: Forgetting where you put your keys is normal ageing; forgetting that you have keys, or being unable to manage finances you previously handled confidently, is not.
Orientation: Getting lost in a familiar neighbourhood, forgetting the current year, or repeatedly asking the same questions within the same conversation are not features of normal ageing.
Language: Dementia often causes word-finding difficulties (anomia) that go beyond occasional tip-of-the-tongue phenomena – difficulty naming common objects, substituting wrong words (paraphasias), or reduced conversational complexity.

Cognitive screening tools used in primary care include the Mini-Mental State Examination (MMSE, scored out of 30) and the more sensitive Montreal Cognitive Assessment (MoCA, also scored out of 30 – below 26 suggests impairment). Cognitive tests alone do not diagnose dementia but guide referral decisions.

Blood tests that identify reversible causes of memory loss

Before attributing memory loss to a neurodegenerative condition, blood tests exclude fully reversible causes – some of which can cause profound cognitive impairment if untreated:

TSH (thyroid function): Hypothyroidism is one of the most important reversible causes of cognitive impairment in older adults – causing slowed thinking, depression, and memory difficulty that can closely mimic early Alzheimer's. Fully reversed with thyroxine treatment.
Vitamin B12: Deficiency causes subacute combined degeneration of the spinal cord and – particularly in older adults – cognitive impairment, personality change, and mood disturbance. B12 below 200 pg/mL is deficient; methylmalonic acid (MMA) is a more sensitive functional marker of deficiency when B12 is borderline (200–300 pg/mL).
Folate: Deficiency causes megaloblastic anaemia and can contribute to cognitive impairment, particularly in combination with B12 deficiency.
Fasting glucose / HbA1c: Poorly controlled diabetes – particularly with recurrent hypoglycaemia – impairs cognition. Insulin resistance is also associated with an increased long-term risk of Alzheimer's disease.
Full blood count: Anaemia causes fatigue and cognitive dulling. The type of anaemia (macrocytic, microcytic) guides further investigation.
Calcium: Hypercalcaemia (from hyperparathyroidism, malignancy, or vitamin D toxicity) causes confusion, fatigue, and memory impairment – the "moans, groans, stones, and bones" tetrad.
Syphilis serology and HIV test: Both cause neurocognitive disorders when untreated. Neurosyphilis is rare but fully treatable.
Liver and renal function: Hepatic encephalopathy and uraemia cause reversible cognitive impairment that can progress to coma if untreated.