The diagnosis of dementia can be met by a certain level of cognitive decline that affects the patient’s ability to function in daily life. However, the causes of dementia are very complex, with nearly one hundred known causes. Therefore, various ancillary tests related to the diagnosis of dementia have emerged. When a patient with cognitive impairment is first seen, the clinician will order neuropsychological measures to assess the presence of cognitive decline and the area and severity of cognitive impairment. Neuropsychometrics is one of the oldest diagnostic tools for dementia and is performed by a specialized neuropsychological rater, with the appropriate tool chosen for different purposes, with varying degrees of complexity. In clinical practice, it has been found that because neuropsychological tests are often done in the form of questions and answers, unlike biochemical and imaging tests that rely on instruments, they often do not receive the cooperation of patients and their families and affect the test results. In fact, for dementia patients, a qualified neuropsychological test is the most important test. Blood biochemistry tests are mainly responsible for differential diagnosis in dementia diagnosis and help to detect treatable causes of cognitive impairment, such as vitamin deficiency, hypothyroidism, infectious diseases, etc. Imaging tests such as CT or MRI can detect intracranial lesions, various etiologies (e.g. tumor, subdural hematoma, hydrocephalus) or other factors that may lead to dementia (e.g. cerebrovascular disease). SPECT and PET is approved for the diagnosis of Alzheimer’s disease in the U.S. and has good sensitivity and specificity for early diagnosis. In recent years, a number of new diagnostic tools for dementia have emerged. These include magnetic resonance volumetric imaging and measurement, cerebrospinal fluid biomarker testing, and PET-specific ligand imaging. The measurement of specific protein concentrations such as beta amyloid and phosphorylated Tau protein allows for an accurate etiological diagnosis of dementia and enables early diagnosis in the preclinical stage of dementia. Studies have shown that the combination of biomarker indicators such as specific proteins in the cerebrospinal fluid can identify early Alzheimer’s disease in patients with preclinical dementia (mild cognitive impairment) with a sensitivity of 95% and a specificity of 83%. Clinical diagnosis of Alzheimer’s disease requires detailed questioning of patients and their families (e.g., spouse or caregiver) about their clinical presentation and progression to determine the presence of cognitive impairment and whether social, occupational, and instrumental activities of daily living are impaired. Operational diagnostic criteria, represented by the National Institute of Neurological Disorders and Stroke – Alzheimer’s and Related Disorders Society (NINCDS-ADRDA) diagnostic criteria, have good sensitivity and specificity (>80%) for differentiating dementia from non-dementia, but are not as accurate (23-88%) for differentiating between different types of dementia.