Occult blood see faecal occult blood
Oestradiol (E2)
Oligoclonal bands see CSF oligoclonal bands
Orexin (CSF) see CSF orexin
Organic acids (serum) - test not available, please request urine organic acids
Orosomucoid - test no longer routinely available. Suggest calprotectin (faeces) for investigation of ?IBD.
Osmolal clearance see fluid balance profile