- O&P Exam- Macro Arthropod
- O&P Exam-Macro Parasite, Worm
- O2 Saturation
- Occult Blood
- Oligoclonal bands
- Opiates (Urine)
- Osmolality (Serum)
- Osmolality (Urine)
- Osmotic Fragility, Red Blood Cell
- Ova and Parasites
- Oxalate
- Oxygen Saturation
- Oxygen, Partial Pressure (Blood)