| Test Name (Click to sort by popular result) | COE Code |
| OKT3 Antibody | SENDOUT |
| Occult Blood, Stool | OCLT |
| Oligoclonal Bands, CSF | OLI BAND |
| Opiate, Urine | UOP/MSOPIATE/UOPTSGL/OPTG |
| Organ Transplant Monitoring Profile | TXPS |
| Organic Acids Screen, Serum | SL MISC |
| Organic Acids, Qualitative, Urine | UOA |
| Organism Identification | ORID/ANID/FNID |
| Ornithine Transcarbamylase Deficiency (OTC) Gene Sequencing | OTCS |
| Orotic Acid, Qualitative, Urine | ORA |
| Osmolality, Serum or Body Fluid | OSMO |
| Osmolality, Urine | OSMOU |
| Osmotic Fragility | ML MISC |
| Osteocalcin | FOSTEO |
| Ova and Parasites, Aspirated Specimen | OPSN |
| Ova and Parasites, Stool | OPE, TRIFEE |
| Ova and Parasites, Urine | SCHIS |
| Ovary Antibody | ML MISC |
| Oxalate, Plasma | ML MISC |
| Oxalate, Urine | OXALATE |
| Oxycodone, Serum | SOXYC |
| Oxycodone, Urine | OXYC |
| Oxymorphone, Urine | ML MISC |