| Abbreviation | Interpretation | 
| X | except | 
|  | extra | 
|  | hourly | 
|  | removal of | 
|  | cross | 
|  | magnification | 
|  | power | 
|  | ten | 
|  | times (multiplied by) | 
|  | extra | 
|  | exposure | 
| X3 | orientation to time, place, and person | 
| Xam | examination | 
| Xanth | xanthomatosis | 
| XBSN | X-linked bulbospinal neuropathy | 
| XC | excretory cystogram | 
| X/C | cross-section | 
| X-CGD | X-linked chronic granulomatous disease | 
| Xcv | Xanthomonas Campestris pv. Vesicatoria | 
| XD | Xanthine dehydrogenase | 
|  | X-ray diffraction | 
| XDH | xanthine dehydrogenase | 
| XDP | xeroderma pigmentosum | 
|  | xanthine diphosphate | 
| Xe | xenon | 
| XECT | xenon-enhanced computed tomography | 
| XEF | excess ejection fraction | 
| XGP | xanthogranulomatous pyelonephritis | 
| XI | Xerostomia Inventory | 
|  | eleven | 
|  | xylose isomerase | 
| XIBV | Xiburema virus | 
| XIC | X-inactivation center | 
| X-IEP | crossed immunoelectrophoresis | 
| XINV | Xingu virus | 
| XIP | x-ray in plaster | 
|  | exchanger inhibitory peptide | 
|  | x-ray-induced polypeptide | 
| XIST | X inactivation specific transcript | 
|  | inactive X chromosome specific transcript | 
| XL | excess lactate | 
|  | Xenopus laevis | 
|  | extended release | 
|  | extra large | 
|  | X-linked (inheritance) | 
| XLA | X linked agammaglobulinaemia | 
| XLAS | X-linked aqueductal stenosis | 
|  | X-linked Alport syndrome | 
| XLCM | X-linked dilated cardiomyopathy | 
| XLD | X-linked dominant | 
|  | xylose lysine desoxycholate | 
| XLH | X-linked hydrocephalus | 
|  | X-linked hypophosphatemia | 
|  | X-linked hypophosphatemic rickets | 
| XLHED | X-linked hypohidrotic ectodermal dysplasia | 
| XLI | X-linked ichthyosis | 
| XLMR | X-linked mental retardation | 
| XLMTM | X-linked myotubular myopath | 
| XLOS | X-linked Opitz syndrome | 
| XLP | X-linked lymphoproliferative syndrome | 
| XLPD | X-linked lymphoproliferative disease | 
| XLR | X-linked recessive | 
| XLRP | X-linked retinitis pigmentosa | 
| XLS | X-linked recessive lymphoproliferative syndrome | 
| XLSP | X-linked spastic paraplegia | 
| XM | crossmatch | 
| XMA | X-ray microanalysis | 
| X-match | crossmatch | 
| XME | xenobiotic-metabolizing enzyme | 
| XMP | xanthine monophosphate | 
| XMMR | Xenopus molecular marker resource | 
| XMR | X-linked mental retardation | 
| XN | xanthohumol | 
|  | night blindness | 
| XO | xanthine oxidase | 
| XOAD | X-linked ocular albinism with deafness | 
| XOM | extraocular movements | 
| XOP | x-ray out of plaster | 
| XOR | exclusive operating room | 
| XP | xeroderma pigmentosum | 
|  | xanthogranulomatous pyelonephritis | 
| XPA | xeroderma pigmentosum group A | 
| XPC | xeroderma pigmentosum group C | 
| XPN | xanthogranulomatous pyelonephritis | 
| XPS | x-ray photoemission spectroscopy | 
| XPTB | extrapulmonary tuberculosis | 
| XR | xray | 
|  | extended release | 
|  | xeroradiography | 
|  | X-linked recessive | 
| XRD | X-ray diffraction | 
| XRE | Xenobiotic response element | 
| XRF | X-ray fluorescence | 
| XRII | X-ray image intensifier | 
| XRMR | X-linked recessive mental retardation | 
| XRN | X-linked recessive nephrolithiasis | 
| XRS | X-ray sensitivity | 
| XRT | X-ray therapy | 
| XS | excessive | 
|  | cross-section | 
|  | xiphisternum | 
| XSA | cross-section area | 
| XSCID | X-linked severe combined immunodeficiency | 
| XSCLH | X-linked subcortical laminar heterotopia | 
| X-SECT | cross-section | 
| XSP | xanthoma striatum palmare | 
| XT | exotropia | 
|  | extra toe | 
|  | extract, extracted | 
| XTM | xanthoma tuberosum multiplex | 
| XTP | xanthosine triphosphate | 
| X-TUL | external tumescent ultrasound liposculpture | 
| XU | excretory urogram | 
|  | X unit | 
| XX | X-ray | 
|  | double strength | 
|  | female chromosome type (homogametic) | 
| XXX | XXX Syndrome (Trisomy X) | 
| XXXX | X chromosome tetrasomy | 
| XY | male chromosome type - two distinct sex chromosomes (heterogametic) | 
| XYL | xylose | 
|  |  |