• Angel Callaway, CPC, CPB

Sequencing of Diagnosis Codes

The selection of diagnosis codes tells the story of a patient’s healthcare encounter. Patients often present with multiple conditions when seeking medical care. Some of these conditions may be related and some may not. Diagnosis selection is critical to obtaining accurate payment for the services rendered.

When telling the patient’s story, you want to make it clear to the payers why the patient sought medical care. Without this story, the payers may deem the services provided as not medically necessary and payment denied.

Sequencing of diagnosis codes helps support the higher-level evaluation and management services (i.e., 99205, 99215)


The reason for the visit drives code sequencing, generally the first-listed diagnosis. It may be followed by co-existing conditions. To accurately select the principal diagnosis and code at the highest degree of specificity, coders must review the provider documentation for the encounter, any associated lab results, outside documentation and apply official coding guidelines found in the coding conventions within the codebook or an encoder, the ICD-10-CM Official Guidelines for Coding and Reporting for the current year or the year that is appropriate for the date of the service.



Some ICD-10 codes are listed as a primary diagnosis code, these codes are always reported first such as Encounter for Z codes (e.g., Z11-Z13, Z36, Z03-Z05, Z09) and indicated in the codebook by Pdx next to the code. If one of these codes is listed in any position other than primary on a claim it will be rejected.


Many ICD-10 codes are followed by guidelines to “Use Additional” instructing the coder to code the underlying condition, followed by etiology and or manifestations. For example when coding Type 2 diabetes with stage three chronic kidney disease, you would code E11.22 followed by N18.3 Chronic kidney disease, Stage 3.


“Code also” convention instructs the coder that two codes may be required to identify the disease process but does not provide sequencing direction, the circumstances of the encounter will determine the sequencing. Example Pt. has secondary pulmonary arterial hypertension in HIV. The reason for the visit is HIV, therefore B20- Human immunodeficiency virus is sequenced first and I27.21 secondary pulmonary arterial hypertension second.


When a definitive diagnosis has not been established signs and symptoms may be reported. When a diagnosis has been established the signs and symptoms that are integral to the disease process should not be reported separately.


“In Diseases Classified Elsewhere” instructs you to code these codes secondary to the etiologic condition. Etiologic conditions are usually listed under the code. For example, when you look up Dementia in other diseases classified elsewhere without behavioral disturbance F02.80, you find instructions to code first the physiological condition (i.e., G30.- Alzheimer’s).


Codes listed in brackets in the Alphabetical index are always listed second. Example A88.0 Enteroviral exanthematous fever followed by [G02] Meningitis in other infectious and parasitic diseases classified elsewhere, the instruction you to code G02 second to A88.0


Following the coding conventions and official guidelines will assist in determining the sequence of diagnosis codes and avoid any unnecessary claim rejections and denials.

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