Who's on First? - Proper Sequencing of Diagnosis Codes

Alicia Krou

Director, Revenue Integrity

For those of you that remember the duo Abbott and Costello, you’ve probably heard the saying “Who’s on First?” many times in your life. Something you might not be as familiar with is “What diagnosis is first?”

The Revenue Integrity Team often sees denials due to the diagnosis codes used and specifically, due to the order of those codes on a claim. We can submit twelve diagnosis codes on a claim, which helps give the insurance carrier a complete picture of the patient’s condition at the time of service. However, insurance carriers use the primary diagnosis to determine medical necessity, as well as benefits and coverage policies. 

Some of the more common issues we see are when patients present for a preventative visit but they also have other chronic conditions. Often times, any/all services being billed for that day have "Routine Exam" (Z00.00) as the primary diagnosis. It would be appropriate to have Z00.00 as the primary diagnosis for the preventive visit but if lab work was also done during that visit for their mixed hyperlipidemia (E78.2), that diagnosis should be primary for those services. 

We have also seen insurance carriers deny claims due to not covering a particular diagnosis or category of diagnoses. Examples of this include obesity or weight loss, anxiety/depression, ADD/ADHD or behavioral related conditions, or even hair loss. In these situations, is there a medical condition that is appropriate? Does the patient have back pain due to their weight?  Are they not sleeping, due to anxiety? We never want to assign the patient a condition they don’t have but signs/symptoms that are present are fair game – sequence those as the primary diagnosis and then use the other codes as a secondary diagnosis.

Hearing someone say “Who’s on First?” might bring a smile to your face but proper sequencing of diagnosis codes can brighten your (and our) day too!