Diabetes Mellitus Coding Challenge

image of diabetes being documented as diagnosis, along with syringe, insulin, and medication to go with the diabetes mellitus coding challenge

**This post was reviewed and updated on October 29, 2023. **

The Coding Challenge


A 32-year-old male patient is diagnosed with type 2 diabetes. He is morbidly obese due to his overeating. A note in the record by the dietician indicates the patient has a BMI of 40.2. Assign the appropriate ICD-10-CM codes.

A. E10.9, E66.01, Z68.41
B. E11.9, E66.01, Z68.41
C. E08.9, E66.9
D. E10.9, E66.09, Z79.4


B. E11.9, E66.01, Z68.41

Locate and Verify

Diabetes, Type 2

Diabetes mellitus (DM) codes are combination codes that include the type of diabetes mellitus, the body system affected, and the complications affecting that body system, if any.

In the above coding scenario, the patient has diabetes and morbid obesity, but no complications are documented.

In the Alphabetic Index, we can look up Diabetes, diabetic (mellitus) (sugar), type 2  E11.9. Then going to this code in the Tabular, we can verify the correct code as:

E11.9, Type 2 diabetes mellitus without complications

There is an instructional note at E11 that states:

“Use additional code to identify control using:

  • insulin (Z79.4)
  • oral antidiabetic drugs (Z79.84)
  • oral hypoglycemic drugs (Z79.84)”

However, the documentation does not indicate the patient uses insulin, oral antidiabetic drugs, or oral hypoglycemic drugs, so we can’t code it.

There are other instructional notes that must be read as well before making the final code selection.

Morbid Obesity

Obesity puts a person at higher risk of developing diabetes and other conditions and should, therefore, be documented and reported. 

In the Alphabetic Index, we can look up Obesity, morbid  E66.01. When going to the Tabular, we can verify the correct code as:

E66.01, Morbid (severe) obesity due to excess calories

There is an instructional note at E66 that states:

“Use additional code to identify body mass index (BMI), if known (Z68.-).”

Body Mass Index (BMI)

The documentation states that the dietician noted the patient’s BMI was 40.2.

When we go to Z68.- in the Tabular, we can see that our correct code is:

Z68.41, Body mass index [BMI] 40.0-44.9, adult 

If the documentation only provides the BMI, we can determine the patient’s overweight severity based on the following:

  • Overweight: BMI = 25.0-29.9
  • Obese: BMI = 30.0-39.9
  • Morbidly obese: BMI = 40+

Note: Pay attention to whether the patient is an adult or infant or child. They are not documented and/or coded in the same way.

BMI Coding Guidelines

The ICD-10-CM Official Guidelines for Coding and Reporting (FY2023) state that code assignment for BMI “is typically, or may be, documented by other clinicians involved in the care of the patient (e.g., a dietitian often documents the BMI…). However, the associated diagnosis (such as overweight, obesity…) must be documented by the patient’s provider. If there is conflicting medical record documentation, either from the same clinician or different clinicians, the patient’s attending provider should be queried for clarification.”

The BMI should only be reported as a secondary diagnosis and should not be assigned during pregnancy.

BMI codes are used in conjunction with codes for any associated condition (i.e., E40-E46, E66.-, D68, R64).

Incorrect Answers

A, C, and D are incorrect.

A. E10.9, E66.01, Z68.41. E10.9 refers to type 1 diabetes mellitus without complications. 

C. E08.9, E66.9. E08.9 refers to Diabetes mellitus due to underlying condition without complications. E66.9 refers to Obesity, unspecified. 

D. E10.9, E66.09, Z79.4. E10.9 refers to type 1 diabetes mellitus without complications. E66.09 refers to Other obesity due to excess calories. Z79.4 refers to Long term (current) use of insulin.

Note: When a patient with type 2 diabetes requires insulin, and it is documented, assign Z79.4. An exception to this rule is when insulin is only given temporarily to bring a secondary diabetic patient’s blood sugar under control during an encounter. In this case, do not assign Z79.4.

If a patient has type 1 DM, Z79.4 should never be reported. However, the documentation should indicate if the patient is being managed with insulin or oral hypoglycemic drugs. A

Additionally, if the patient has gestational diabetes, Z79.4 should not be assigned.

Final Thoughts

Something to keep in mind here that may help you find the answers more quickly as you go through a timed exam:

Look at the answers before you read the question.

  • At quick glance, I can see that options A and D both have E10.9 listed; A and B both have E66.01 and Z68.41; and only option D has code Z79.4.
  • I can also see that option C is the only one that does not have a Z code.
  • And because I know my mnemonics, I can see that the E codes listed are found in the chapter on Endocrine, Nutritional, and Metabolic Diseases (E00-D89). In fact, I may have had a lot of coding practice up to this point and know that E10.9, E11.9, and E08.9 are diabetes mellitus codes.
  • I may even know that Z79.4 is the code for long-term use of insulin, as well as guidelines for when this should be assigned.

Whatever you can gather from the answers quickly before reading the question can really speed up the process.

Leave a Reply

Your email address will not be published. Required fields are marked *