| OAT | Oat IgE | — |
| OBPR | OB Profile | CBC6 - Fluorescence Flow Cytometry, Hydrodynamic Focusing, and Cyanide-free SLS methods; TYIAS - Column Agglutination; HBSG, RUBBIGG, SYPAB - Electrochemiluminescence Immunoassay |
| OBHIV | OB Profile w/ HIV test | CBC6 - Fluorescence Flow Cytometry, Hydrodynamic Focusing, and Cyanide-free SLS methods; TYIAS - Column Agglutination; HBSG, RUBBIGG, SYPAB - Electrochemiluminescence Immunoassay; HIVABS - Real-time PCR (nucleic acid amplification test) |
| GBLD | Occult Blood, Gastric | — |
| ZYPA | Olanzapine (Zyprexa) | — |
| OLGNL | Oligoclonal Banding in CSF and Serum | — |
| ONION | Onion IgE | — |
| CDOPI | Opiate Confirmation, Urine | — |
| OPIAS | Opiates, Serum or Plasma, Quant | — |
| OPIT | Opiates, Urine Quant | — |
| ORANGE | Orange, IgE | — |
| ORXNA | Orexin-A/Hypocretin-1, Spinal Fluid | — |
| OARU | Organic Acids, Random Urine | — |
| OPOX | Orthopoxvirus by PCR | — |
| OSMT | Osmolality, 24 Hour Urine | — |
| OSMRPS | Osmolality, Blood | — |
| FOS | Osmolality, Fecal | — |
| UOSMRPS | Osmolality, Urine | — |
| OSMF | Osmotic Fragility | — |
| OSTEO | Osteocalcin | — |
| OISEQ | Osteogenesis Imperfecta & Low Bone Density Panel, Seq | — |
| OPBF | Ova & Parasite Exam, Body Fluid or Urine | — |
| OPPIN | Ova & Parasite, Pinworm Exam | — |
| OVPAR | Ova & Parasites, Stool Complete | — |
| OVAARU | Ova and Parasite | GLAM, CRYSPOR - Qualitative Enzyme Immunoassay |
| OVALB | Ovalbumin IgE | — |
| OVOMUC | Ovomucoid IgE | — |
| OXA | Oxalate | — |
| UOX | Oxalate, 24 Hr. Urine | — |
| ROXUR | Oxalate, Random Urine | — |
| OXCRBZ | Oxcarbazepine/Eslicarbazepine Metabolite | — |
| OXLDL | Oxidized Low-density Lipoprotein (OxLDL) | Enzyme-linked immunoassay (ELISA) |
| OMFP | Oxycodone and Metabolite Free Blood Test | — |
| OXYCMU | Oxycodone/Oxymorphone, Screen ONLY, Urine | Immunoassay (IA) |
| OYSTER | Oyster IgE | — |
