Can I claim a medical expense on a lab incurred in 2017 if it was paid in 2018? I do not have insurance so every medical expense I claim adds up.

It is considered an older bill, but it was unknown at the time. Doctor messed up the address when sending the bill so it took a while to find it.

So if this procedure was done in 2017, and paid in 2018 in full, would it be claimable on the next years taxes?