Q&A: Driving the bus for DRG assignment

Q: If the principle diagnosis ICD-9 code is on the MCC list but there is no other diagnosis for the patient, is the DRG assigned with MCC or without?

For example, patient presents with heart failure but has no other diagnoses. So the ICD-9 code is 428.21, acute systolic heart failure. Would this fall into MS-DRG 291 or 293?

A: If a diagnosis is the principal diagnosis it can’t also be an MCC. It can’t drive the bus and be a passenger at the same time. In your example, if the heart failure is the principal diagnosis (the bus driver), you’d need to find another diagnosis to act as the MCC (a passenger) to group to DRG 291.  For example, any DRG that says “with” in the description (with CC, with MCC with CC/MCC) needs both a bus driver (principal diagnosis) and at least one passenger (CC, MCC, CC/MCC)

However, there is a little quirk about heart failure that is an exception to the rule. If the physician states “heart failure” or “congestive heart failure (CHF)” as the principal diagnosis your beginning ICD-9 code would be 428.0 (heart failure, unspecified as to type).

If the CDI specialist queries the provider to determine whether there is an association between “hypertension” (if appropriate) and “heart failure” (not an assumed relationship) and the provider documents “hypertensive heart disease”   what the coder would assign is a combination code as the principal diagnosis, 402.91 Hypertensive heart disease, unspecified, with heart failure (for example).  The instructional notes (in the code book) instruct the coder to assign an additional code from the 428* series of codes to describe the type of heart failure (e.g., 428.21, acute systolic heart failure).

In this scenario, the coding would include:

• Principal diagnosis (bus driver): 402.91, hypertensive heart disease, unspecified, with heart failure
• Secondary diagnosis (passenger): 428.21, acute systolic heart failure
• MS-DRG: 291, Heart failure with MCC

If the patient also has hypertension (and or chronic kidney disease) it can be very important to query for the association between hypertension (and CKD, if appropriate) and heart disease, and the heart failure so one of these combination codes can be assigned (as the principal diagnosis). Then the patient’s specific type of heart failure may act as the MCC in certain cases.

Editor’s Note: This question was answered by Lynne Spryszak, RN, CCDS, CPC. At the time of this article's original release, she was a Chicago-based Independent Healthcare Consultant.