APR-DRGs

The All-Patient Refined Diagnosis Related Group information on each encounter is calculated by 3M's APR-DRG grouper software licensed by Clinical Analytics Software.

Clinical Analytics references the Grouping types of your Analysis Profile for severity and risk adjustments. We recommend using APR-DRGs for inpatient encounters for most situations because it provides the most detailed level of comparison. Each of the 315 base APR-DRGs has 4 levels of SOI (Severity of Illness) and 4 levels of ROM (Risk of Mortality), giving 1260 possible benchmark levels.

Other resources

  • Here is a full list of APR-DRG descriptions.
  • For more information and examples about when you should choose the MS-DRG grouping type, see MS-DRGs.
  • For history and comparisons of these groupers, check out the APR-DRG vs MS-DRG webinar on the Webinars page.

What are APR-DRGs for?

Based on the diagnosis and procedure codes for an inpatient encounter, the grouper assigns an APR-DRG, SOI, and ROM. By categorizing encounters by APR-DRG, we are grouping them by similar clinical conditions. Typically, each APR-DRG relates to a specific body system, so knowing the APR-DRG, SOI, and ROM of a patient encounter provides quite a bit of statistical and clinical information about the case and allows us to make valid measure comparisons between facilities. Basically, we can expect cases of the same APR-DRG and SOI combination to require about the same amount of resources for treatment; this provides very powerful insight into our analytics. Further, we can expect cases of the same APR-DRG and ROM combination to see approximately the same mortality rate.

Assigning APR-DRG, SOI, and ROM

Clinical Analytics Software licenses APR-DRG grouping software from 3M to calculate the APR-DRG, SOI, and ROM. There is extensive clinical logic accounting for procedure and diagnosis codes when making the assignments. For each APR-DRG, there is an individual model for classifying each SOI and ROM. Because of this, it is important to not average SOI or ROM between APR-DRGs unless you are sure of your analytic intent.

NOTE: While the levels of SOI and ROM are ordinal (an SOI 4 is far more sick than an SOI 1), this is not a linear relationship. An SOI 3 is not necessary three times as sick as an SOI 1 case.

DRG Weights

The primary reasons for risk-adjusting measure values is because we expect certain types of patients to require more resources than others. By retrieving benchmark values by APR-DRG/SOI, we are comparing similar patients when analyzing resource usage.

To help accommodate for this variability in resource usage, 3M calculates weights for every APR-DRG/SOI combination. These weights are accounted for in the CMS Case Mix Index measure; see Case Mix Index calculation for more information. This allows us account for patient Severity of Illness when aggregating multiple SOIs and/or APR-DRGs.

To help demonstrate this concept, see the chart below, which plots the weights for all 4 SOI levels of 6 APR-DRGs on a number line. Keep in mind that ROM follows a similar pattern with mortality risk.

  • First notice that there is a correlation between the SOI and the weight, as we expect. There are mostly SOI 1's to the left side (low weight) and mostly SOI 4's to the right side (high weight), indicating that SOI 4 patients typically require more resources that SOI 1 patients.
  • Upon closer inspection, we see that this relationship does not hold between DRGs. Notice APR-DRG 101 (Cystic Fibrosis Pulmonary Disease) SOI 1 has a weight of 1.2019 while APR-DRG 776 (Other Drug and Dependence) SOI 3 has a weight of only .7991.

NOTE: For this reason, we do not average SOI (or ROM) across APR-DRG. We incorporate the weight assignment when calculating Case Mix Index (CMI) and always risk-adjust benchmark values to account for this known resource usage variability.

SOI vs ROM

Similarly, SOI and ROM operate independently. While we often see similar numbers between the two characteristics, it is not unusual to have an SOI 1 and ROM 4, or vice versa. With the exception of mortality measures, all benchmarks are calculated at the APR-DRG/SOI level.

SOI

Severity of Illness takes into account the extent of the damage to the body system the APR-DRG is associated with. Keeping this in mind, note that an SOI of 4 is not the same for a broken bone versus sepsis, for example. This calculation only considers diagnoses and procedures associated with the body system.

ROM

Risk of Mortality relates to the expected mortality rate for patients. This takes into account all diagnoses and procedures for the case. As with SOI, there is a unique model for ROM for each APR-DRG. All mortality measure benchmarks are calculated at the APR-DRG/ROM level.