There are many guidelines associated with assigning ICD-10-CM codes, requiring coders to carefully study them out to understand the intricacies of each. On top of the rules just associated with identifying a code for reporting purposes, there are also rules about which codes can be reported together, which are bundled, and those that have special sequencing guidelines. Combination codes are among these types of services that have special guidelines just for them. Combination codes reduce the complexity of ICD-10 coding by combining multiple codes into just one that provides higher specificity.

According to the ICD-10-CM Official Guidelines, 

“A combination code is a single code used to classify two diagnoses, a diagnosis with an associated secondary process (manifestation), or a diagnosis with an associated complication”

Terms Identifying a Causal Relationship for Combination Codes

A causal relationship, in diagnostic coding, is one in which disease is identified as being caused by another disease or condition. Some examples include, chronic kidney disease caused by chronic hypertension, or retinopathy caused by diabetes. 

Identifying and Assigning Combination Codes

According to the ICD-10-CM Official Coding Guidelines, certain linking terms, when identified in the medical record automatically represent a causal relationship when they appear in the code title, such as: “with”, “in”, “associated with”, and “due to”.

The guidelines also provide clarity on how to identify and assign combination codes,

“The word “with” or “in” should be interpreted to mean “associated with” or “due to” when it appears in a code title, the Alphabetic Index (either under a main term or subterm), or an instructional note in the Tabular List. The classification presumes a causal relationship between the two conditions linked by these terms in the Alphabetic Index or Tabular List.”

When you search in the alphabetic list for a main term, such as hypertension and there is a subterm “with” followed by other diseases, if the patient has one of these other diseases (e.g., heart failure), then this linking term “with” pulls the two diagnoses together into a single code for reporting purposes. 

The guidelines go on to explain, 

“These conditions should be coded as related even in the absence of provider documentation explicitly linking them, unless the documentation clearly states the conditions are unrelated or when another guideline exists that specifically requires a documented linkage between two conditions (e.g., sepsis guideline for “acute organ dysfunction that is not clearly associated with the sepsis”).“

If you review the documentation and there is a specific provider statement verifying these two conditions are not related to each other, then the linking term “with” can be ignored and the codes reported separately. However, if there isn’t, then these conditions should be reported with the combination code and not separately. It does not matter if heart failure is listed first in the assessment and plan and hypertension is listed further down, separately or even as a condition in the history of present illness. If both are present in the documentation and there is not a statement clarifying they are unrelated, then they are reported as a combination code. 

There are combination codes for other conditions that do not include this linking language in the Alphabetic Index. For these types of conditions, if you search the main term, you will not see “with”, “due to”, “in”, or “associated with”. These are still combination codes, but they have another requirement. When these two conditions are present in the same encounter and the provider does not purposely state they are linked, they are not reported as a combination code, but rather they are reported individually, as clarified in the guidelines.

“...Conditions not specifically linked by these relational terms in the classification or when a guideline requires that a linkage between two conditions be explicitly documented, provider documentation must link the conditions in order to code them as related. The word “with” in the Alphabetic Index is sequenced immediately following the main term or subterm, not in alphabetical order.”

Let’s identify a combination code in the following assessment and plan example: 

Assessment and Plan

1. Hyponatremia, likely from CHF
2. CKD Stage III Creatinine (mg/DL) on 6.20.22 was 1.70 (H) and 6.19.22 was 1.99(H). Will consider diuresis if cardiology suggests and pressures continue to improve. Regular diet for now. BMP ordered.
3. HFpEF, chronic. Recent admission on 5.4.22 for HFpEF with large pericardial effusion seen on TTE. Discussed with interventional cardiology. Hold digoxin, coreg, losartan, and spironolactone for now. Reduce torsemide to 40 mg BID.
4. Chronic atrial fibrillation, on apixaban 2.5 mg BID.
5. Hypertension-Hold carvedilol and losartan. Re-start as outpatient.
6. DVT prophylaxis with subcutaneous Lovenox

Searching the Alphabetic Index under “hypertension” we identify linking language “with” connecting to subterms, “heart failure” (HFpEF) and “chronic kidney disease,” resulting in the final combination code of: 

I13.0 - Hypertensive heart and chronic kidney disease with heart failure and stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney disease

Use additional code to identify type of heart failure (I50.-)

Use additional code to identify stage of chronic kidney disease (N18.1-N18.4, N18.9)

In the example, we see three distinct conditions listed individually in the Assessment and Plan that are all represented in one combination code. The code description has linking language between all three conditions, making it appropriate to report with a single code, rather than three individual codes. 

If you, as a coder, think about how often you see certain conditions reported together, you will begin to see a pattern of when combination codes might exist. Look for linking language in the Alphabetic Index, with conditions such as, diabetes, hypertension, heart disease, pregnancy-related conditions, spinal conditions, heart failure, ulcers, sepsis, and conditions due to drugs, medicaments, and biological substances, which are all examples of conditions reportable with combination codes.

Additional Points to Consider: 

• Combination codes provide additional specificity for better code assignment.
• Query providers when the documentation is unclear or it appears that a condition should be linked but linking language, when required, is missing from the documentation. 
• In addition to the combination code, additional codes may be required for complete coding, such as the patient’s BMI, disease stage, or other associated factor.