Question Z code as primary?


Dallas Texas
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I am studying the cases in the COPC book and case 2 answers Z79.899 listed as primary dx, I am under the impression that it should not be coded as primary. Please help me try to understand this, thanks


True Blue
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It would be unusual to see Z79.899 as a primary diagnosis, but there is no rule I know of that says it cannot be one. Some Z codes may only be primary (e.g. Z00.00), and a few have specific instructions that they cannot be first (e.g. Z15- codes) or have guidelines that require another code must be listed first (e.g. Z79.82), but Z79.899 is not one of these. There's a section in the guidelines for the Z codes (quoted below) that details all of this. Hope that helps some.

Per the ICD-10 Guidelines for Chapter 21:
Z codes are for use in any healthcare setting. Z codes may be used as either a first-listed (principal diagnosis code in the inpatient setting) or secondary code, depending on the circumstances of the encounter. Certain Z codes may only be used as first-listed or principal diagnosis.


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Usually, when using a Z code referring to use of medications, the primary code is for the disease being treated by the medication being taken.

For example, if you have a patient taking Plaquenil for Rheumatoid arthitis your coding order would be:

1) Code for rheumatoid arthritis
2) Your Z79.899
3) If the patient is found to have an adverse effect from the medication, you have to look up the Plaquenil up by its generic name, hydroxyquinolone, in the Table of Drugs and Chemicals and put that T code as the third diagnosis code. Remember to add the appropriate A, D or S character at the end.

Tom Cheezum, OD, CPC, COPC
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