ANNALS EXPRESS: A rapid and sensitive fluorescence method for detecting urine formaldehyde in patients with Alzheimer's disease.

BACKGROUND: Morning urine formaldehyde (FA) levels could predict the severe degree of dementia in patients with post-stroke dementia (PSD) and Alzheimer's disease (AD). However, the routinely available technique of high-performance liquid chromatography (HPLC) for detecting urine FA requires expensive and sophisticated equipments.

METHODS: We established a fluorescence spectrophotometric method by using a FA-specific fluorescent probe- NaFA (λex/em = 430/543 nm). As a standard reference method, the same batch of urine samples was analyzed by HPLC with a fluorescence detector (λex/em = 346/422 nm). Then we compared the limits of detection (LOD) and the limits of quantization (LOQ) detected by these two methods, and addressed the relationship between urine FA and human cognitive ability. The Mini-Mental State Examination (MMSE), Clinical Dementia Rating (CDR) and Activities of Daily Living Scale (ADL) were used to evaluate cognition function in 30 AD patients and 52 healthy age-matched controls.

RESULTS: LOD and LOQ (1.27 and 2.48 M) of the NaFA probe method were more accurate than Fluo-HPLC (1.52 and 2.91 M). There was no difference in the detected FA values within day and day-to-day. Notably, only 3/82 urine FA concentrations detected by NaFA probe were below zero; while 12/82 of the values analyzed by Fluo-HPLC were abnormal. More importantly, there were negatively correlated between urine FA levels detected by NaFA probe and MMSE scores, but positively correlated with CDR scores in AD patients.

CONCLUSIONS: This detecting FA method by NaFA probe was more rapid, sensitive and accurate than Fluo-HPLC.