One study published in the International Journal of Legal Medicine found that ketamine can be detected in hair up to 4 months after a single dose.11 Ketamine and its metabolites were also detected in scalp samples collected by a wet cotton swab up to 48 hours after administration of the drug. In a study of urine samples collected from hospitalized children who had received ketamine as an anesthetic, ketamine could be detected in the urine up to 11 days after drug administration and its metabolites could be detected for up to 14 days.12
https://americanaddictioncenters.org/ketamine-abuse/how-long-does-ketamine-stay-in-your-system
So he went 11 days free of ketamine?
What? Oh god no. He bought clean pee. Probably while on Special K.
This is the way my boss told me to do it to make sure I passed.