| 0020588 | Occult Blood, Fecal (1-3 Determinations) |
| 2007190 | Occult Blood, Fecal by Immunoassay |
| 0060310 | Occult Blood, Gastric |
| 2004061 | Octamer Transcription Factor-2 (Oct 2) by Immunohistochemistry |
| 2004058 | Octamer Transcription Factor-3 and -4 (Oct 3/4) by Immunohistochemistry |
| 2005656 | Ogden Syndrome (NAA10) Sequencing Exon 2 |
| 0098833 | Olanzapine |
| 0080440 | Oligoclonal Band Profile |
| 0081135 | Oligoclonal Bands in CSF and Serum |
| 0092354 | Opiates - Confirmation/Quantitation - Serum or Plasma |
| 0090364 | Opiates - Confirmation/Quantitation - Urine |
| 2005096 | Opiates, Screen Only, Urine |
| 2005093 | Opiates, Screen with Reflex to Confirmation, Urine |
| 0099289 | Organic Acids, Plasma |
| 0098389 | Organic Acids, Urine |
| 0060720 | Organism Identification by 16S rDNA Sequencing |
| 2004892 | Ornithine Transcarbamylase Deficiency (OTC) Deletion/Duplication |
| 2004901 | Ornithine Transcarbamylase Deficiency (OTC) Sequencing |
| 2004896 | Ornithine Transcarbamylase Deficiency (OTC) Sequencing and Deletion/Duplication |
| 0092458 | Orotic Acid and Orotidine, Urine |
| 0098122 | Osmolality, Fecal |
| 0020046 | Osmolality, Serum or Plasma |
| 0020228 | Osmolality, Urine |
| 2002257 | Osmotic Fragility, Erythrocyte |
| 0020728 | Osteocalcin by Electrochemiluminescent Immunoassay |
| 2002277 | Ova and Parasite Exam, Body Fluid or Urine |
| 2002272 | Ova & Parasite Exam, Fecal (Immunocompromised or Travel History) |
| 2007394 | Ovarian Antibody Screen with Reflex to Titer by IFA |
| 0090708 | Oxalate, Serum or Plasma |
| 0020482 | Oxalate, Urine |
| 0091387 | Oxazepam, Serum or Plasma |
| 0098834 | Oxcarbazepine Metabolite |
| 2005103 | Oxycodone/Oxymorphone Screen Only, Urine |
| 2005100 | Oxycodone/Oxymorphone Screen with Reflex to Confirmation, Urine |
| 2002984 | Oxygen Dissociation (P50) by Hemoximetry |
