| Abbreviations | Meaning |
 | NMTCB | Nuclear Medicine Technology Certification Board |
| NNEB | National Nursery Examination Board |
| NOA | National Optometric Association; Nitro-L-arginine |
| NOTB | National Ophthalmic Treatment Board |
| NOV | Nederlandse Orthopaedisch Vereniging (Dutch Orthopaedic Association) |
| NPA | National Pharmaceutical Association |
| NRHA | National Rural Health Association |
| NRPB | National Radiological Protection Board |
| NSA | National Stroke Association |
| NSA | Neurological Society Of America |
| NSCC | National Society For Crippled Children |
| NSCIA | National Spinal Cord Injury Association |
| NSCT | National Society Of Cardiovascular Technologists |
| NSGC | National Society Of Genetic Counselors |
| NSH | National Society For Histotechnology |
| NSMR | National Society For Medical Research |
| NSNA | National Student Nurse Association |
| NSPB | National Society For The Prevention Of Blindness |
| NWDA | National Wholesale Druggists' Association |
| NWDA | National Wholesale Druggists Association |
| NWOTA | North West Orthopaedic Trainees Association |
| NYHA | New York Heart Association |
| NYHAFC | New York Heart Association Functional Class |
| OAA | Old Age Assistance; Older Americans Act; Opticians Association Of America; Oxaloacetic Acid |
| OARS | Osteoarthritis Research Society |
| OATA | Ohio Athletic Trainers Association |
| OLSNA | Orthopaedic Laser Society Of North America |
| OMRT | Ontario Association Of Medical Radiation Technologists |
| ONS | Oncology Nursing Society |
| OOSS | Outpatient Ophthalmic Surgery Society |
| ORA | Orthopaedic Rehabilitation Association (AAOS Specialty Societies) |
| ORS | Orthopaedic Research Society (also: AAOS Specialty Societies) |
| ORS | Orthopaedic Research Society |
| ORS-ROC | Orthopedic Research Society, Republic Of China |
| OSA | Optical Society Of America |
| OSMT | Ontario Society Of Medical Technologists |
| OSTOP | Osteoporosis Society Of British Columbia |
| OSUK | Ophthalmological Society Of The United Kingdom |
| OTA | Orthopaedic Trauma Association (Newsletter) (also: AAOS Specialty Societies) |
| PACT | Philadelphia Association Of Clinical Trials |
| PAFAMS | Pan-American Federation Of Associations Of Medical Schools |
| PASSOR | Physiatric Association For Spine, Sports, And Occupational Rehabilitation |
| PCB | Paracervical Block; Polychlorinated Biphenyl; Portacaval Bypass; Postcoital Bleeding; Printed Circuit Board; Procarbazine |
| PCBA | Printed Circuit Board Assembled |
| PDRB | Permanent Disbility Rating Board |
| PDS | Patient-Doctor Society |
| PERT | Phenol-enhanced Reassociation Technique; Program Evaluation Review Technique |
| PFOLA | Prescription Foot Orthotic Laboratory Association |
| PHA | Public Health Association |
| PMA | Pharmaceutical Manufacturers Association |
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