The Generative Brain

Tests explained

The main tests are an MRI brain scan, an EEG recording of brain activity, and a lumbar puncture whose fluid goes to a national laboratory for the RT-QuIC test and for markers called 14-3-3 and tau. A blood test can look at the prion protein gene, and brain tissue examination is what confirms a diagnosis.

Tests at a glance
Brain imaging and activity
  • MRI
  • EEG
Spinal fluid
  • RT-QuIC
  • 14-3-3 and tau
Genetic
  • PRNP gene sequencing
  • After counselling
In research
  • Skin and nasal samples
  • Blood and urine tests

Each test below answers a different question. No single one of them gives the whole answer, which is why doctors look at them together.

MRI brain scan

The person lies still inside a scanner for half an hour or so. It is noisy and painless. The scan can show a pattern of bright areas in particular parts of the brain that doctors associate with prion disease. Certain scan settings show this best, so it helps if the radiologist knows what the team is looking for. The scan also looks for other causes of the same symptoms, such as a stroke or a tumour.

EEG

Small pads are placed on the scalp with paste and record the brain’s electrical activity for about half an hour. Nothing is given and nothing hurts. In sporadic CJD the recording sometimes shows a particular repeating pattern. A normal EEG does not rule the illness out.

Lumbar puncture and the spinal fluid tests

A doctor numbs the skin of the lower back and takes a small amount of the fluid that surrounds the brain and spinal cord with a fine needle. It takes a few minutes and some people have a headache afterwards for a day or two.

The fluid is sent to a national prion laboratory for three tests. RT-QuIC detects the misfolded prion protein itself by letting it build up in the tube until a machine can see it. On spinal fluid it is right about nine times in ten when the illness is present, and it very rarely reads positive in people who do not have it. It is less reliable for some of the rarer forms, including fatal familial insomnia and Gerstmann-Straussler-Scheinker disease, so a negative result does not always settle the question. The other two, 14-3-3 and tau, rise when brain cells are being damaged by any cause, so they support a picture without naming the illness.

Results take time. At the United States national centre the laboratory work alone takes five working days from the day the sample arrives.

Blood test of the prion protein gene

A standard blood sample can be used to read the prion protein gene and look for an inherited change. For someone who is already ill, the neurology team usually arranges this. For a relative who is well, this is predictive testing, and it starts with a genetic counsellor, before any blood test. Choosing not to be tested is a complete answer.

Tests still being studied

Brushing the lining high in the nose picks up the same misfolded protein and has performed about as well as spinal fluid in research. Skin samples are being studied too, with better results when more than one small sample is taken. A 2026 review reports that blood tests are close to use in the clinic, and that tears and urine are being studied. These are research tests in most places today, and your hospital may not be able to offer them.

For variant CJD, the form linked to BSE in cattle, a tonsil biopsy can show the abnormal prions.

Brain tissue

Examining brain tissue is the only way to confirm the diagnosis. A biopsy during life is rarely done, and only when doctors suspect a different illness that could be treated, because the operation has its own risks. Examination after death is the usual route, and in some countries a national registry arranges and pays for it when the family consents.

How prion disease is diagnosed puts these in order. Questions for your doctor helps with the next appointment, diagnosis and tests is the overview, and the Atlas tests pages hold the technical records.

What any result means for one person is a question for the neurologist who ordered it.

Sources for this page