Pets

You might also see ARNP - Advanced Registered Nurse Practitioner, or APN - Advanced Practice Nurse.

Then, just to throw a few more letters in the alphabet soup:

Here are some abbreviations for different types of nurse practitioners:
ACNP: Acute Care Nurse Practitioner
ANP: Adult Nurse Practitioner
APRN: Advanced Practice Registered Nurse
CRNP: Certified Registered Nurse Practitioner
CNP: Certified Nurse Practitioner
FNP: Family Nurse Practitioner
GNP: Gerontological Nurse Practitioner
NNP: Neonatal Nurse Practitioner
NP: Nurse Practitioner
PMHNP: Psychiatric Mental Health Nurse Practitioner
PNP: Pediatric Nurse Practitioner
SNP-BC: School Nurse Practitioner
WHNP: Women's Health Nurse Practitioner

The main difference between NPs and PAs is that NPs are educated on the nursing model for health care, which is generally more whole patient focused, and PAs are educated on the traditional medical model of care. All NPs are RNs first. PAs usually do not come from a nursing background.

In many states, an NP can open his or her own practice if they wish to do so. PAs must have a collaborative agreement with a "supervising" physician who may or may not be on site.

(retired peds NP here)