Based upon recent clinical and research studies in conjunction with the availability of commercial diagnostic testing, the following conclusions can be made on biomarker tests for the assessment of AD or related dementia:
- Several biomarkers are currently available for the diagnostic assessment of individuals with symptoms of AD or related dementia. However, no specific biomarker or panel of biomarkers is currently used to make a definitive diagnosis of AD. The definitive diagnosis of AD can only currently be made after death using microscopic examination of brain tissue.
- The most widely used biomarkers for AD are the AB 42 peptide, the AB42/40 ratio, total Tau protein, phospho-tau protein and the APOE e4 isoform. Although whole blood may be used as a specimen source for various biomarkers, the main specimen source continues to be CSF.
- Because CSF biomarkers involve an invasive and high cost spinal tap procedure for collection of the specimen, blood-based biomarker assays for AD have been developed and are currently available. Blood-based biomarkers have the advantage of being less invasive and less costly specimen collection procedure. At present, blood-based biomarker testing for AD is mainly being used by dementia researchers rather than by physicians in clinical settings.
- In clinical practice, CSF biomarkers are used mainly as an aid in the diagnosis of AD to improve on the accuracy of the diagnosis especially in cases involving unusual presentation of symptoms or with rapidly progressive dementia.
- For research studies, AD biomarkers are being used to study the early detection, prevention and effects of potential treatments. Researchers are using both blood and CSF biomarkers to study risk factors and genetic variants involved in AD and also to select patients for clinical trials and research studies.
- Although biomarkers may help, the actual diagnosis of AD is typically made by exclusion or using other tests including a variety of cognitive tests and PET scanning to rule out other conditions that may cause similar symptoms.
- The future of biomarkers for the assessment and diagnosis of AD and other dementias looks promising. Developing new biomarkers especially blood-based assays that are more sensitive, less expensive and/or less invasive may help to improve upon the accuracy for AD diagnosis. Also, new and improved biomarker assays may allow for better assessment of disease progression, and help to identify AD and related dementias at an earlier stage where treatment may be more beneficial.