If I drank 18 beers on Thursday and had a urine drug screen on the following Tuesday afternoon approx 110 hours later, Would I pass??

"If" denotes a hypothetical situation. Hypothetically, you should pass.

Now, in reality, if you are supposed to abstain from drinking it would be ill advised to chance the test being moved up or something strange happening and you fail.

If you actually drank the 18 beers and are due to take the test, you stand a good chance of being okay. I won't say definitely that you will pass because there are very few absolutes in life and the human body.

Is what you stand to lose worth 18 beers and days of stress?

Since you are way past 80 hours, you should test negative.

What about next time? 18 beers would seem to indicate this isn't the first time.

18 beers in ONE day indicates a serious drinking problem. One that needs to be faced and dealt with.