Yes, you can choose how to pay for medical claims.
If you have funds available in your PCA, claims will be paid out of your PCA first. If you want to use a different pre-tax benefit account to pay your medical bills, you can turn off your PCA (online). In some cases, you may have to pay the cost of the services upfront. Pharmacy claims will always be paid out of your PCA, as long as you have funds available.