Differences that Impact MS-DRGs: Unstable Angina Made Foolproof

In my last blog, I talked about an instance in which ICD-10 eliminated the code for an acute manifestation available in ICD-9 (esophageal hemorrhage), how that impacts projected ICD-10 MS-DRG reimbursement (it goes down a little), and what you can do about it (make sure the documentation and coding is up to snuff so the specified cause and associated hemorrhage are coded).

In this example, ICD-10-CM has not eliminated an acute manifestation code available in ICD-9—the one for specifying unstable angina (a type of chest pain). Here it is, alive and kicking:  I20.0 Unstable angina. Rather than eliminate something, ICD-10-CM has added a series of combination codes that specify the most common underlying cause of unstable angina: coronary artery disease (CAD).  Here is an example: I25.110 Atherosclerotic heart disease of native coronary artery with unstable angina pectoris. This means that in ICD-10-CM, when a patient has CAD and unstable angina, only one code is needed instead of the two  separate codes needed in ICD-9. This also means that in ICD-10, you can’t dink around with the sequencing of principal diagnosis. A good thing in this case, but also a possible MS-DRG difference between ICD-9 and ICD-10.

In ICD-9,  when a patient has CAD and unstable angina, the acute manifestation code 411.1 Intermediate coronary syndrome  (aka unstable angina) is paired with one of the CAD codes, like 414.01 Coronary atherosclerosis of native coronary artery. Since they are two physically separate codes, it would seem that either one of the two could be listed as the principal diagnosis—but would that be correct coding? No. Coding guidelines say unambiguously that when CAD is documented along with angina, the CAD code should be listed as the principal diagnosis. In ICD-9 MS-DRGs, a correctly coded record lists the CAD code first, and the MS-DRG is 303 Atherosclerosis.

But the data tells us that 200+ per million Medicare records are sequenced the other way round, with the angina code listed as the principal diagnosis and the CAD code as a secondary.  Even sadder, the MS-DRG assigned in those 200+ per million records is actually lower in the DRG hierarchy—311 Angina pectoris.

So what does this mean for possible impact to your organization? First, if in your analysis you predict a significant number of DRG shifts from 311 in the ICD-9 MS-DRGs to 303 in the ICD-10 version, this is most likely due to historically bad ICD-9 coding that will simply go away in ICD-10. Why? Because it is next to impossible to sequence the record incorrectly in ICD-10. To do that, a coder would have to commit several cardinal sins:

• Ignore the fact that combination codes for CAD with angina exist
• Code the two codes separately, and willfully disregard the language in the code titles which makes them mutually exclusive
  • I25.10 Atherosclerotic heart disease of native coronary artery without angina pectoris
  • I20.0 Unstable angina
  • Sequence the two codes incorrectly according to prominent and exhaustively discussed coding guidelines

Hopefully you do not know any coders like that, and so it’s all good news: your ICD-10 records for patients with CAD and unstable angina will be coded and sequenced correctly, MS-DRG assignment will be correct, and all will be right with the world.

For this flavor of MS-DRG impact, the CAD with angina example is a pretty painless one: the problem lies in ICD-9, plus bad ICD-9 coding, and life gets better under ICD-10. These are all popular things to say. But there are other not-so-easy examples of the same principle at work—where a single stand-alone acute manifestation code in ICD-9 is preserved in ICD-10, but also augmented by additional combination codes that tie the acute manifestation to its underlying cause. In other examples, the MS-DRG may shift in a less fun direction, and the guidelines for sequencing are not so clear cut. We’ll noodle through one such example in the next blog.

Rhonda Butler is a Senior Clinical Research Analyst with 3M Health Information Systems.