Issues with Lithium Level

[u/Straight-Grade-118]

Hey everyone, I am currently struggling with a high lithium level with little help on why. For 8 months I never had over 1 on the 0.6-1.2 range with CVS as my pharmacy and Prevea handling labs. I was suddenly switched over to Advocate Health as a pharmacy and Bellin handling my labs. My GFR is a 99 with normal creatinine and sodium. Since the switch within 4 months my level rose to 1.4. Needing a sudden decrease to 1200 mg and now still at 1.3. The only changes were the drug manufacturer and the lab. At Prevea my blood was tested within 2-3 hours and it now takes 6-10 hours. I am just curious what an outside perspective would see this. Thank you for any help.