After 2 hours post-ingestion, only 1% to 10% of LSD will have remained unchanged in urine, the rest will consist of inactive, water-soluble metabolites (e.g. 2-oxo-3-hydroxy LSD). Though LSD is rapidly metabolized and processed, it is thought to remain in the blood, brain, and other organs in varying amounts for up to 8 hours.
From the first result in a bing search for LSD metabolites.
“Though LSD is rapidly metabolized and processed, it is thought to remain in the blood, brain, and other organs in varying amounts for up to 8 hours.”
Well, the average trip lasts 8-12 hours so obviously something is remaining in the body longer than 8 hours...
Unless you are a Scientologist, then you believe "micro crystals" of LSD can lodge in capillaries and break loose at random and unexpected times years and years later, causing flashbacks and making the person a risk to those around him.
Needless to say they have a way to get rid of these micro crystals, involving nutrition, sweating in a sauna and lots and lots of running, and massive donations to the church to supervise the program, of course...