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DESCRIPTIONAlzheimer’s disease (AD) is invariably diagnosed clinically, focusing on the exclusion of other causes of dementia. In 1984, the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and the Alzheimer’s and Related Disorders Association (ADRDA) developed clinical criteria for the diagnosis of AD. Three categories were defined: possible, probable, and definite AD. The diagnosis of definite AD requires a brain biopsy confirming the presence of characteristic neurofibrillary tangles. While definite AD is almost always diagnosed by autopsy, in approximately 85% of those with a diagnosis of probable AD, pathological findings are found to be consistent. The diagnostic categories are defined as follows:
Possible Alzheimer's Disease
Probable Alzheimer's Disease
The criteria for the clinical diagnosis of probable AD include:
The diagnosis of probable AD is supported by:
Other clinical features consistent with the diagnosis of probable AD, after exclusion of causes of dementia other than AD, include
Features that make the diagnosis of probable AD uncertain or unlikely include;
Definite Alzheimer's Disease
Accompanying advances defining the AD phenotype and pathophysiology “research criteria for the diagnosis of Alzheimer’s disease” have been recently proposed including clinical features, neuroimaging, genetic markers, and biomarkers. However, existing evidence and current practice relies on the NINCDS/ADRDA classifications.
Because diagnosis of AD can be difficult for both physicians, patients, and families there has been considerable interest in identifying an accurate laboratory test for AD - particularly for use early in the course of disease. Abnormal cerebrospinal fluid (CSF) levels of the tau protein (phosphorylated [P-tau] or with a threonine moiety [T-tau]) or an amyloid beta (AB) peptide such as AB-42 have been found in patients with AD. Other potential CSF peptide markers have also been explored. The tau protein is a microtubule-associated molecule that is found in the neurofibrillary tangles that are typical of AD. This protein is thought to be related to degenerating and dying neurons, and high levels of tau proteins in the CSF have been associated with AD. AB-42 is a subtype of amyloid beta peptide that is produced following the metabolism of amyloid precursor protein. AB-42 is the key peptide deposited in the amyloid plaques characteristic of AD. Low levels of AB-42 in the CSF have been associated with AD, perhaps because AB-42 is deposited in amyloid plaques instead of remaining in solution. Finally, investigators have suggested the Tau/AB-42 ratio a potentially more accurate diagnostic marker than either alone.
Neural thread protein is another protein that is associated with neurofibrillary tangles of Alzheimer's disease. Both CSF and urine levels of this protein have been investigated as a biochemical marker of Alzheimer's disease. Urine and CSF tests for neural thread protein may be referred to as the AD7CTM test, as developed by Nymox Pharmaceutical Corporation.
Genetic testing for Alzheimer's disease has also been investigated and is considered separately in the Genetic Testing for Familial Alzheimer's Disease medical policy.
POLICYMeasurement of cerebrospinal fluid biomarkers of Alzheimer's disease, including but not limited to tau protein, amyloid beta peptides, or neural thread proteins, is considered investigational.
Measurement of urinary biomarkers of Alzheimer's disease is considered investigational, including but not limited to neural thread proteins.
POLICY GUIDELINESInvestigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY7/2003: Approved by Medical Policy Advisory Committee (MPAC)
9/2/2003: Code Reference section completed
12/17/2008: Policy reviewed, no changes
05/13/2010: Policy description updated with new research findings; policy statement unchanged. Added CPT codes 83520 and 83912, which are used to identify the steps in testing for tau protein and amyloid beta peptides. There are no specific codes used for testing for neural thread protein.
07/29/2011: Policy reviewed; no changes.
11/28/2012: Policy reviewed; no changes.
05/06/2013: Removed ICD-9 diagnosis code 331.0 from the Code Reference section.
11/15/2013: Policy reviewed; no changes.
SOURCE(S)Blue Cross Blue Shield Association policy # 2.04.14
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.