| X0 | Nervous System |
| X2 | Cardiovascular System |
| X9 | Ear, Nose, Sinus |
| XD | Gastrointestinal System |
| XE | Physiological Systems and Anatomical Regions |
| XF | Hepatobiliary System and Pancreas |
| XH | Skin, Subcutaneous Tissue, Fascia and Breast |
| XK | Muscles, Tendons, Bursae and Ligaments |
| XN | Bones |
| XR | Joints |
| XT | Urinary System |
| XU | Female Reproductive System |
| XW | Anatomical Regions |
| XX | Physiological Systems |
| XY | Extracorporeal |