Coding Diabetes Mellitus in ICD-10-CM: Improved Coding for Diabetes Mellitus Complements Present Medical Science

By Karen M. Kostick, RHIT, CCS, CCS-P

Results of a recent coding and clinical documentation pilot study indicate that the ICD-10-CM coding classification changes made for diabetes mellitus have significantly improved coding for this disease. The results of the study noted that although a few ICD-10-CM "unspecified" diabetes codes were assigned, the majority of the diabetes codes sufficiently captured the diagnoses as expressed in the clinical documentation.

In addition, the pilot study noted that the ICD-10-CM diabetes codes complement present medical science-separate type 1 and type 2 diabetes category codes and body system combination codes are a major improvement over ICD-9-CM. Instead of classifying as controlled or uncontrolled, ICD-10-CM classifies inadequately controlled, out of control, and poorly controlled diabetes mellitus by type with hyperglycemia. This article highlights key ICD-10-CM features for diabetes mellitus coding.

In ICD-10-CM, chapter 4, "Endocrine, nutritional and metabolic diseases (E00-E89)," includes a separate subchapter (block), Diabetes mellitus E08-E13, with the categories:

• E08, Diabetes mellitus due to underlying condition
• E09, Drug or chemical induced diabetes mellitus
• E10, Type 1 diabetes mellitus
• E11, Type 2 diabetes mellitus
• E13, Other specified diabetes mellitus

The diabetes mellitus categories E08–E13 are further subdivided into four- or five-character subcategories. When a category has been subdivided into four-, five-, or six-character codes, the diabetes code assigned represents the highest level of specificity within ICD-10-CM.

ICD-10-CM Tabular Instructional Notes

Diabetes mellitus tabular inclusions notes are introduced by the term "Includes" and appear at the beginning of a category. Categories E10–E13 inclusion notes further define or provide examples of the content within each category, as illustrated in the sidebar.

The "Excludes1" note meaning "not coded here" appears under all the diabetes mellitus categories. An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note.

Similar to ICD-9-CM, "Code first" and "Use additional code" notes are present for some of the diabetes mellitus categories and subcategories that require the underlying condition be sequenced first, followed by the manifestation. The Use additional code note appears at the etiology code and a Code first note at the manifestation code.

ICD-10-CM diabetes codes are combination codes that include the type of diabetes mellitus, body system affected, and the complications affecting that body system. The following examples apply ICD-10-CM chapter 4, "Diabetes mellitus E08-E13," tabular list instructions and illustrate diabetes mellitus code combinations and code specificity.

First, suppose a patient is seen for diabetic chronic kidney disease, stage 3. The patient has type 2 diabetes and takes insulin on a daily basis. The appropriate code assignments would be:

• E11.22, Type 2 diabetes mellitus with diabetic chronic kidney disease
• N18.3, Chronic kidney disease, stage 3 (moderate)
• Z79.4, Long term (current) use of insulin

There is a combination code for the type 2 diabetes with chronic kidney disease, and the tabular instructs the coder to use an additional code to identify the stage of the chronic kidney disease. At the E11 category level, the Use additional code note instructs the coder to identify insulin use.

In another case, a female patient with type 1 diabetes is seen for severe nonproliferative diabetic retinopathy with macular edema. The coding here would be:

• E10.341, Type 1 diabetes mellitus with severe nonproliferative diabetic retinopathy with macular edema

No additional codes are necessary because there is a combination code for the type 2 diabetes with nonproliferative diabetic retinopathy with macular edema.

Finally, consider a type 2 diabetic patient evaluated for a chronic diabetic left foot ulcer with necrosis of muscle. The patient takes insulin on a daily basis. The coding would follow:

• E11.621, Type 2 diabetes mellitus with foot ulcer
• L97.523, Non-pressure chronic ulcer of other part of left foot with necrosis of muscle
• Z79.4, Long term (current) use of insulin

Code L97.523 is assigned based on the note under code E11.621 which states to use an additional code to identify site of ulcer (L97.4-L97.5). Code Z79.4 is assigned based on the E11 category level, Use additional code note to identify insulin use.

In addition to chapter 4, accurate ICD-10-CM diabetes mellitus coding requires proficiency in many other chapters as well. For example, category E08, Diabetes mellitus due to underlying condition, instructs to code first the underlying condition such as cystic fibrosis, malignant neoplasm, pancreatitis. Category E09, Drug or chemical induced diabetes mellitus, instructs to code first the applicable drug or toxin (T36-T65) for poisonings.

When reporting diabetes in pregnancy, many codes in chapter 15, "Pregnancy, childbirth and the puerperium (O00-O9A)," include a final character indicating the trimester of pregnancy. This character is valuable since poorly controlled diabetes during the second and third trimesters can result in excessively large babies, causing medical risk to both mother and newborn.

For example, a 32-year-old female patient with type 1 diabetes is G2, P1, 26 weeks and is seen to evaluate her diabetes in pregnancy. The codes for this case would be:

• O24.012, Pre-existing diabetes mellitus, type 1, in pregnancy, second trimester
• Z3A.26, 26 weeks gestation of pregnancy

The provider's clinical documentation of the trimester (or number of weeks) for the current admission or encounter informs the final character's assignment. The time frames for the trimesters are indicated at the beginning of chapter 15.

In chapter 19, "Injury, poisoning and certain other consequences of external causes (S00-T88)," category T85, Complications of other internal prosthetic devices, implants, and grafts, is used to report diabetic insulin pump complications. Category T85 requires the appropriate seventh character added to each code to describe the encounter type (A: initial encounter, D: subsequent encounter, S: sequela).

So if a type 1 diabetic patient is seen in the ED for an initial encounter to evaluate the leakage of her insulin pump, then the code assignment would be:

• T85.633A, Leakage of insulin pump, initial encounter
• E10.69, Type 1 diabetes mellitus with other specified complication

Chapters 16, "Certain conditions originating in the perinatal period;" 18, "Symptoms, signs, and abnormal clinical and laboratory findings, not elsewhere classified;" and 21, "Factors influencing health status and contact with health services" also provide codes in relation to diabetes mellitus.

References

Moczygemba, Jackie, and Susan H. Fenton. "Lessons Learned from an ICD-10-CM Clinical Documentation Pilot Study." Perspectives in Health Information Management. Winter 2012. http://perspectives.ahima.org.

Centers for Medicare and Medicaid Services. "2012 ICD-10-CM and GEMs." https://www.cms.gov.

Centers for Disease Control and Prevention. "2011 National Diabetes Fact Sheet." www.cdc.gov/diabetes/pubs.

National Center for Health Statistics. "ICD-10-CM Official Guidelines for Coding and Reporting 2012." Available under "Tools and Resources" at www.cdc.gov/nchs.

AHIMA. ICD-10-CM Coder Training Manual. Chicago, IL: AHIMA Press, 2012.

Karen Kostick (karen.kostick@ahima.org) is a director of professional practice at AHIMA.