Dementia diagnostics

Tau protein and ß-amyloid in the cerebrospinal fluid

General points and pathogenesis
Dementia, which is essentially a clinical diagnosis, is characterised by changes in personality and the inability to remember things. Alzheimer’s disease, a neuronal degenerative disease, is the most common cause of dementia, followed by multi-infarct dementia, which is the atherosclerosis of small CNS arteries with multiple CNS infarcts. Mixed forms occur, which are difficult to distinguish clinically. A reliable diagnosis of Alzheimer’s disease or Alzheimer’s dementia can only be achieved by conducting a brain biopsy. For histopathology, evidence of neurofibrillary tangles and senile plaques needs to be found. The main components of these structures are hyperphosphorylated forms of the Tau protein and the ß-amyloid.

Diagnostics
The Tau protein is an intracellular neural protein that is released in all degenerative diseases of the nervous system and is then found in an elevated concentration in the cerebrospinal fluid. This is helpful for differential diagnostics when distinguishing Alzheimer’s disease from Creutzfeldt-Jakob disease, where it can be found in very high concentrations in the CSF.
For histopathology, it is necessary to detect plaques in the brain that contain ß-amyloid when diagnosing Alzheimer’s disease. The plaque formation results in a high „consumption” of ß-amyloid in the cerebrospinal fluid; the concentration is therefore significantly decreased in patients with Alzheimer’s disease.

Test material
Only CSF in polypropylene tubes (request from the laboratory), at least 250 µl of cerebrospinal fluid per request.

Shelf life: 4 °C for approx. 1 week

Result
Tau protein: the reference range is age-related.
Up to 60 years: < 150 ng/l
over 60 years: < 275 ng/l

Diagnosis

< 300 ng/lno Alzheimer’s
300 - 450 ng/lAlzheimer’s cannot be excluded
> 450 ng/lSuspected Alzheimer’s disease
> 1530 ng/lSuspected Creutzfeldt-Jakob disease

Bacterial meningitis or an adrenoleukodystrophy can cause false positive values.

ß-amyloid < 550 ng/l: Suspected Alzheimer’s disease

The use of polystyrene or glass vessels may result in falsely lowered values being found.

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