Peth score

I recently went to detox because the mental health place i was going to requiered it. I’ve been drinking half a litre of 40% everyday for 6 months and they told me my peth was only at 0.81 µmol/L or 569 ng/mL. I find my score to be VERY low considering the amounts ive drank. Read that 10% of the population makes less peth than whats normal. What do you think? What was your number and how much+long did you drink for?