major diagnostic category major diagnostic category the major diagnostic categories (mdc) are formed by dividing all possible principal diagnoses (from icd-9-cm) into 25 mutually exclusive diagnosis areas. mdc codes, like diagnosis-related group (drg) codes, are primarily a claims and administrative data element unique to the united states medical care reimbursement system. drg codes also are mapped, or grouped, into mdc codes. the diagnoses in each mdc correspond to a single organ system or cause and, in general, are associated with a particular medical specialty. mdc 1 to mdc 23 are grouped according to principal diagnoses. patients are assigned to mdc 24 (multiple significant trauma) with at least two significant trauma diagnosis codes (either as principal or secondaries) from different body site categories. patients assigned to mdc 25 (hiv infections) must have a principal diagnosis of an hiv infection or a principal diagnosis of a significant hiv related condition and a secondary diagnosis of an hiv infection. mdc 0, unlike the others, can be reached from a number of diagnosis/procedure situations, all related to transplants. this is due to the expense involved for the transplants so designated and because these transplants can be needed for a number of reasons which do not all come from one diagnosis domain. drgs which reach mdc 0 are assigned to the mdc for the principal diagnosis instead of to the mdc associated with the designated drg. list of major diagnostic categories mdc description ms-drg 0 pre-mdc 001 - 017 1 diseases and disorders of the nervous system 020 - 103 2 diseases and disorders of the eye 113 - 125 3 diseases and disorders of the ear, nose, mouth and throat 129 - 159 4 diseases and disorders of the respiratory system 163 - 208 5 diseases and disorders of the circulatory system 215 - 316 6 diseases and disorders of the digestive system 326 - 395 7 diseases and disorders of the hepatobiliary system and pancreas 405 - 446 8 diseases and disorders of the musculoskeletal system and connective tissue 453 - 566 9 diseases and disorders of the skin, subcutaneous tissue and breast 573 - 607 10 diseases and disorders of the endocrine, nutritional and metabolic system 614 - 645 11 diseases and disorders of the kidney and urinary tract 652 - 700 12 diseases and disorders of the male reproductive system 707 - 730 13 diseases and disorders of the female reproductive system 734 - 761 14 pregnancy, childbirth and puerperium 765 - 782 15 newborn and other neonates (perinatal period) 789 - 795 16 diseases and disorders of the blood and blood forming organs and immunological disorders 799 - 816 17 myeloproliferative dds (poorly differentiated neoplasms) 820 - 849 18 infectious and parasitic dds (systemic or unspecified sites) 853 - 872 19 mental diseases and disorders 876 - 887 20 alcohol/drug use or induced mental disorders 894 - 897 21 injuries, poison and toxic effect of drugs 901 - 923 22 burns 927 - 935 23 factors influencing health status and other contacts with health services 939 - 951 24 multiple significant trauma 955 - 965 25 human immunodeficiency virus infection 969 - 977 mdc category missing 981 - 989; 998,999