Why do reference range vary from lab to.

My main question is i did a hiv/cd4/cd3/cd8 count and all came normal, within the reference range. However, for example: somewhere i saw cd4/cd8 ratio is normal at 2.0 and below 1.0 means you likely have HIV. However, my lab reference range was 0.36-1.90. My result was 1.03 and they hv shown it as normal. But when i googled it, it said normal is 2.0 but my lab reference range shows 0.36-1.90 and mine is normal. So i am extremely confused on which parameter and reference range should i rely myself on? Many say different labs hv different parameters so it's best to rely on the particular lab from where you hv done your tests. Is it true? Please help me clear the air of confusion. Would be extremely obliging, thank you.