PMC patient severity scale: derivation and validation - Patient Management Category

Health Services Research, August, 1994 by Wanda W. Young, Susan Kohler, Jeanne Kowalski

After patient types were designated by physician panels, codes in the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) were mapped to the categories to computerize the classification. The resultant PMC Classification software uses the unique combination of ICD-9-CM diagnosis and procedure codes recorded on a patient's computerized discharge abstract to assign one or more clinically specific PMCs to that patient.(2) Unlike other classifications that are driven by the principal diagnosis code listed on the patient's abstract (such as DRGs), PMCs disregard the sequence or order in which the diagnosis codes are listed to identify all comorbid conditions as well as specific complications. It is the way in which these codes are aggregated and the interrelationship of diagnosis codes that is critical to the accurate identification of clinical patient types and the valid assignment of PMCs to patients.

An example will illustrate the importance of recognizing the relationship among diagnosis codes for accurate classification. Table 1 shows the comorbid conditions (two PMCs) of one patient with five ICD-9-CM diagnosis codes. Two codes describe the clinical manifestation (perforation) of the patient's diverticular disease while three of the codes listed are related to the patient's AMI and related complication (cardiogenic shock). The Patient Management Category computerized algorithm searches the list of diagnosis codes to determine the general disease(s) that were treated in that hospitalization-in this case, Diverticular Disease and Acute Myocardial Infarction (AMI). Within each of these disease areas, which are modules or subroutines of the PMC Software, the combination of related diagnosis codes is recognized by the software and used to make the clinically specific PMC assignment(s). The same two PMC assignments would be made for this patient regardless of the order of the diagnosis codes recorded on the patient's computerized record.

The term "comorbid" means that more than one disease or pathological condition is present, not that there is more than one diagnosis code present. It should also be emphasized that comorbid patients are not necessarily more severely ill or more costly to manage than patients with a single disease. That is, a patient can be comorbid with two relatively minor conditions, each requiring few hospital resources for effective management. Therefore, the identity of the particular comorbid conditions will determine the severity of the patient's illness, the intensity of resources required to managed that patient, and the resultant cost of care.

Table 1: Example of PMC Assignment Process

ICD-9- CM Diagnosis                 PMC Assignment                 PMC-R1S

569.83 Perforation of intestine    ^ 0104 Diverficular Disease:
562.11 Diverticulitis of colon     ^ Peritonitis/Perforation       1.79

427.81 Sinoatrial node dysfunction ^
410.11 Acute myocardial infarction ^ 0308 AMI: Cardiogenic Shock   2.76
of other anterior wall             ^
785.51 Cardiogenic shock           ^

Comorbid combination                                               3.75