These key facts are from healthdirect.gov.au (accessed 05 November 2026). Visit the healthdirect website for more information about Alzheimer's disease.
Laboratory tests are increasingly being used along with a clinical assessment and brain imaging, to help diagnose Alzheimer's disease and guide treatment decisions.
Biomarkers
Blood and cerebrospinal fluid (CSF) tests can measure biomarkers that reflect the changes happening in the brain due to Alzheimer’s disease. These changes include a build-up of amyloid beta protein (plaques) and abnormal forms of tau protein (tangles). CSF tests measure amyloid beta (Aβ42/40) and tau proteins in the fluid surrounding your brain and spinal cord. Newer blood tests are much less invasive because they do not require a lumbar puncture.
Other blood tests such as vitamin B12, thyroid function, full blood count, electrolytes, calcium, glucose and kidney and liver function tests are used to rule out conditions that can cause similar memory and thinking problems.
Two important blood biomarkers are p-tau217 and p-tau181, which are abnormal forms of the tau protein that rise when amyloid beta and tau changes are present due to Alzheimer’s disease. p-tau217 testing is the more accurate of the two and a positive result supports a diagnosis but cannot confirm it without other tests. Another biomarker, neurofilament light chain (NfL), reflects damage to nerve cells but is not specific to Alzheimer’s disease.
Genetic testing
Genetic testing is used in some circumstances. Testing for changes in the APOE gene can show whether a person is at an increases risk for Alzheimer’s disease. This test cannot diagnose the disease or tell whether someone will develop it. It would usually be offered is there was a family history of APOE-associated Alzheimer’s disease or if someone had Alzheimer’s disease at a particularly young age. APOE testing is also done before starting some newer anti-amyloid treatments because people with the APOE ε4 variant have a higher risk of side effects such as brain swelling or bleeding.
Testing for variants in the PSEN1, PSEN2 and APP genes is used when a rare inherited form of Alzheimer’s disease called early -onset familial Alzheimer’s disease (EOFAD) is suspected. This form of the disease usually develops before the age of 65 and runs in families. Genetic counselling is recommended before and after these tests.