I heard that med bills can't be counted towards credit scores. Is that true? What do I do about this mess?

I owe money to Quest Diagnostics, a large company that does lab work. I have hypothyroidism and my dr was having me come in for several blood tests a year, at a point, as often as once a month, till the thyroid levels in my blood were steady and healthy & my meds seemed like the right dose for me. there were a few yearly physical exams w/ blood tests as well. Some visits I was uninsured others i was (when i got F/T hrs w/ benefits) but cuz I was diagnosed with my condition prior to joining, they wouldnt cover it (prediagnosis) for the first year of the plan. All occured over a few years, off the top of my hear I think the first visit was oct/nov 2004? First collections called a lot but i didnt answer & it just stopped one day. There was a while when I got letters by mail each one trying to sound more serious/threatening than the last. They didnt stop but slowed down tons. I need my debt total so I can plan payment.Bill says amount due for indiv visit. Sent separately but inconsistantly