CPT® Code 84393

The CPT® Code 84393 refers to the testing of phosphorylated tau proteins, specifically pTau 181 and pTau 217, which are critical biomarkers in the assessment of Alzheimer’s disease. Neurofibrillary tangles, which are formed by the abnormal accumulation of tau protein in the brain, represent one of the two primary neuropathological features associated with Alzheimer’s disease. These tangles develop within neurons as a result of the hyperphosphorylation of tau, a process that typically occurs following the formation of beta-amyloid plaques, the first hallmark of the disease. Notably, the pathological build-up of hyperphosphorylated tau can begin 10 to 15 years prior to the onset of clinical symptoms, indicating its potential role in early diagnosis. Among the tau proteins, pTau 217 has emerged as a more recent and promising blood-based marker. An elevated level of pTau 217 is indicative of the neuropathological changes characteristic of Alzheimer’s disease. While both pTau 181 and pTau 217 levels are elevated in individuals with clinical Alzheimer’s, pTau 217 may offer superior differentiation between Alzheimer’s disease and other frontotemporal lobe degenerative disorders, as it is a more robust indicator of amyloid activity and tau binding observed in the temporal cortex through PET imaging. The testing for these proteins is conducted using electrochemiluminescence-based assays, and the appropriate CPT® code for each protein tested is 84393, while the total tau test is reported under code 84394.