Most LEDs are rated for reverse leakage current at 10uA.
Some are rated at 100uA.
They are all rated at -5V as the absolute maximum rated voltage.
From reading thousands of LED data sheets, I have never seen any LED spec'd less than 1uA max although this doesn't mean they all perform this way.
I did a spot check at Digikey
- 100uA max 5mm C503B-RCN-CW0Z0AA1 Cree RED
- 100uA max 5mm LTL-4223-R1 Lite-ON RED
- 10 uA max 3mm TLDR4400 Vishay Deep RED
I believe leakage current is related the limited number of minority carriers near the junction but this gets swamped by material impurities and also increases with damage from ESD or overvoltage from my experience.
My supplier specs are 1uA for Red Yellow LEDs AlinGaAs and 10uA for Blue White.