Chapter 4 — Endocrine, Nutritional and Metabolic Diseases
Diabetes as combination coding: type, body system and complication in a single code — plus the insulin and drug status codes, pump malfunctions, and the obesity class rules.
Chapter 4 is dominated by diabetes mellitus, and the single most important fact about the diabetes codes is that they are combination codes — each one carries the type of diabetes, the body system affected and the complication affecting that body system. You assign as many codes from E08–E13 as are needed to describe every associated condition the patient has, sequenced according to the reason for the encounter.
Which diabetes category applies?#
| Documentation | Category | Notes |
|---|---|---|
| Type 1 diabetes mellitus | E10.- | Also called juvenile diabetes. Age is not the sole determining factor, though most type 1 diabetics develop the condition before puberty |
| Early-stage type 1 diabetes predating the onset of symptoms | E10.A- | Presymptomatic type 1 diabetes mellitus |
| Type 2 diabetes mellitus | E11.- | — |
| Type 2 diabetes without complications, in remission | E11.A | Assigned on provider documentation of remission. QUERY If unclear, query — the guideline states that the term resolved is not synonymous with remission |
| Type not documented | E11.- | ALWAYS Type 2 is the default |
| Type not documented, but the patient uses insulin | E11.- | Still type 2, plus the appropriate Z79 code |
| Diabetes due to an underlying condition | E08.- | Secondary diabetes — always caused by another condition or event |
| Drug or chemical induced diabetes mellitus | E09.- | Secondary diabetes |
| Other specified diabetes mellitus | E13.- | Secondary diabetes |
| Diabetes in pregnancy, childbirth or the puerperium | O24.- first, then E08-E13 | See Section I.C.15.g and I.C.15.i |
Long-term drug status codes with diabetes#
| Treatment documented | Assign |
|---|---|
| Insulin only | Z79.4 Long term (current) use of insulin |
| Oral hypoglycemic drugs only | Z79.84 |
| Injectable non-insulin antidiabetic drugs only | Z79.85 |
| Oral hypoglycemic drugs and insulin | Z79.4 and Z79.84 |
| Insulin and an injectable non-insulin antidiabetic drug | Z79.4 and Z79.85 |
| Oral hypoglycemic drugs and an injectable non-insulin antidiabetic drug | Z79.84 and Z79.85 |
| Insulin given temporarily to bring a type 2 patient's blood sugar under control during an encounter | NEVER Z79.4 is not assigned |
The same table applies to secondary diabetes mellitus — guideline I.C.4.a.6.a repeats it in full for patients with E08, E09 or E13 who routinely use these drugs, including the rule that Z79.4 is not assigned where insulin is given only temporarily.
Insulin pump malfunctions#
| Event | Sequence |
|---|---|
| Underdose of insulin due to insulin pump failure | 1T85.6- Mechanical complication specifying the type of pump malfunction, as the principal or first-listed code2T38.3X6- Underdosing of insulin and oral hypoglycemic drugs3codes for the type of diabetes mellitus and any associated complications due to the underdosing |
| Overdose of insulin due to insulin pump failure | 1T85.6- as the principal or first-listed code2T38.3X1- Poisoning by insulin and oral hypoglycemic drugs, accidental (unintentional) |
| Postpancreatectomy diabetes | Assign |
|---|---|
| Lack of insulin due to surgical removal of all or part of the pancreas | E89.1 Postprocedural hypoinsulinemia |
| Code sequence | A code from category E13 as the principal or first-listed diagnosis, with Z90.41- Acquired absence of pancreas as an additional code |
Obesity and obesity class#
| Code | Covers |
|---|---|
E66.- | Overweight and obesity — including codes for the cause, such as E66.1 drug-induced obesity, and for the effects, such as E66.2 morbid (severe) obesity with alveolar hypoventilation |
E66.81- | Obesity class — requires a 5th character conveying the severity. The obesity class must be documented by the provider for these codes to be assigned |
E88.82 | Obesity due to disruption of MC4R pathway |
O99.21- | Obesity complicating pregnancy, childbirth and the puerperium |
| Class 3 obesity and morbid obesity both documented | ALWAYS Assign only the class 3 obesity code — it is more specific |
The obesity class codes may be reported with other obesity codes found in Chapters 4 and 15 to fully describe the condition. The one restriction is the class 3 and morbid obesity overlap above.
Practice questions#
Q1An office note documents “insulin-dependent diabetes mellitus” with no statement of type anywhere in the record. What is assigned?
- A
E10.9andZ79.4 - B
E11.9andZ79.4 - C
E11.9only - D
E13.9andZ79.4
Show answer & rationale
Correct answer: B. E11.9 and Z79.4
Rationale. Guideline I.C.4.a.3 provides that if the documentation does not indicate the type of diabetes but does indicate that the patient uses insulin, E11.- type 2 diabetes mellitus should be assigned, with an additional code from category Z79 to identify the long-term use of insulin. Guideline I.C.4.a.2 sets E11.- as the default where the type is not documented at all.
Q2A type 2 diabetic is admitted with pneumonia and receives a sliding-scale insulin drip for two days to control blood glucose during the acute illness. She takes only metformin at home. Which status codes are assigned?
- A
Z79.4andZ79.84 - B
Z79.4only - C
Z79.84only - DNeither code
Show answer & rationale
Correct answer: C. Z79.84 only
Rationale. Guideline I.C.4.a.3 states that Z79.4 should not be assigned if insulin is given temporarily to bring a type 2 patient's blood sugar under control during an encounter. The home metformin is long-term oral hypoglycemic therapy, so Z79.84 is assigned. The same restriction on Z79.4 is repeated at I.C.4.a.6.a for secondary diabetes.
Q3A patient's insulin pump fails, delivering less insulin than prescribed, and she presents with hyperglycaemia. What is the principal diagnosis?
- A
T38.3X6- - B
E11.65 - C
T85.6- - D
E11.9
Show answer & rationale
Correct answer: C. T85.6-
Rationale. Guideline I.C.4.a.5.a directs that an underdose of insulin due to an insulin pump failure is assigned to a code from subcategory T85.6 that specifies the type of pump malfunction, as the principal or first-listed code, followed by T38.3X6- underdosing of insulin and oral hypoglycemic drugs, then codes for the type of diabetes and any associated complications due to the underdosing. The same principal code applies to a pump malfunction causing an overdose, with T38.3X1- second.
Q4The provider documents both “class 3 obesity” and “morbid obesity” for the same patient. What is assigned?
- ABoth codes
- BOnly the code for class 3 obesity
- COnly the code for morbid obesity
- DOnly
E66.9
Show answer & rationale
Correct answer: B. Only the code for class 3 obesity
Rationale. Guideline I.C.4.b.1 states that if both class 3 obesity and morbid obesity are documented, only a code for class 3 obesity should be assigned as it is more specific. The obesity class codes in subcategory E66.81 otherwise may be reported with other obesity codes in Chapters 4 and 15 to fully describe the condition, and require the class to be documented by the provider.
Q5A patient developed diabetes after a total pancreatectomy for pancreatic cancer. How is the diabetes reported?
- A
E11.-as the default, withZ90.41- - BA code from category
E13as the principal or first-listed diagnosis, withZ90.41-as an additional code - C
E08.-with the malignancy sequenced first - D
E89.1alone
Show answer & rationale
Correct answer: B. A code from category E13 as the principal or first-listed diagnosis, with Z90.41- as an additional code
Rationale. Guideline I.C.4.a.6.b.i covers secondary diabetes mellitus due to pancreatectomy: for postpancreatectomy diabetes mellitus, meaning lack of insulin due to the surgical removal of all or part of the pancreas, assign E89.1 postprocedural hypoinsulinemia, and assign a code from category E13 as the principal or first-listed diagnosis with a code from subcategory Z90.41 acquired absence of pancreas as an additional code.
Scenarios#
A patient with type 2 diabetes mellitus is seen in the office. The provider documents diabetic stage 3a chronic kidney disease, diabetic polyneuropathy and diabetic macular oedema of the right eye with proliferative retinopathy. The visit focused chiefly on the worsening kidney function. The patient takes insulin and a sodium-glucose co-transporter 2 inhibitor long term.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | E11.22 | Type 2 diabetes mellitus with diabetic chronic kidney disease — first-listed, because the encounter focused on the kidney disease |
| 2 | N18.31 | Chronic kidney disease, stage 3a |
| 3 | E11.42 | Type 2 diabetes mellitus with diabetic polyneuropathy |
| 4 | E11.3511 | Type 2 diabetes with proliferative diabetic retinopathy with macular edema, right eye — verify the exact code in the Tabular List |
| 5 | Z79.4 | Long term (current) use of insulin |
| 6 | Z79.84 | Long term (current) use of oral hypoglycemic drugs, if applicable to the agent documented |
Rationale. Guideline I.C.4.a states that the diabetes codes are combination codes including the type, the body system affected and the complication, that as many codes within a category as are necessary may be used, that they are sequenced based on the reason for the particular encounter, and that as many codes from E08-E13 as needed should be assigned to identify all associated conditions. Guideline I.C.9.a.2 and I.C.14.a require N18.- to identify the CKD stage. The Z79 codes follow I.C.4.a.3. Confirm which long-term agent classes the patient actually takes before selecting between Z79.84 and Z79.85.
Guideline: Section I.C.4.a, I.C.4.a.3, I.C.14.a
A patient on long-term high-dose corticosteroid therapy for giant cell arteritis develops diabetes mellitus, documented by the provider as steroid-induced. The corticosteroid was correctly prescribed and properly administered.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | E09.9 | Drug or chemical induced diabetes mellitus without complications — sequenced per the Tabular List instructions at E09 |
| 2 | T38.0X5- | Adverse effect of glucocorticoids and synthetic analogues, with the appropriate 7th character |
| 3 | Z79.52 | Long term (current) use of systemic steroids, if documented |
Rationale. Guideline I.C.4.a.6 identifies E09 as the category for drug or chemical induced diabetes mellitus and notes that secondary diabetes is always caused by another condition or event, naming an adverse effect of a drug among the causes. Guideline I.C.4.a.6.b.ii cross-references Section I.C.19.e for the coding of adverse effects. Guideline I.C.19.e.5.a requires that for an adverse effect of a correctly prescribed and properly administered drug, the nature of the adverse effect is coded followed by the drug code with 5th or 6th character 5. Sequencing of the E09 code relative to the cause follows the Tabular List instructions at that category, per I.C.4.a.6.b.
Guideline: Section I.C.4.a.6, I.C.4.a.6.b, I.C.19.e.5.a
A hospital dietitian documents a BMI of 44.1. The attending physician documents “class 3 obesity”. The patient is admitted for an elective knee replacement.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | Reason for admission | the osteoarthritis code that occasioned the admission, as principal diagnosis |
| 2 | E66.813 | Obesity class 3 — verify the 5th character in the Tabular List |
| 3 | Z68.41 | Body mass index 40.0-44.9, adult — secondary diagnosis only |
Rationale. Three guidelines combine. Section I.B.14 permits BMI to be coded from a clinician other than the patient's provider, such as a dietitian, but requires the associated diagnosis to be documented by the provider and restricts BMI codes to secondary diagnoses. Section I.C.21.c.3 repeats that BMI codes should only be assigned when there is an associated, reportable diagnosis documented by the patient's provider, and prohibits BMI codes during pregnancy. Section I.C.4.b.1 requires the obesity class to be documented by the provider, which it is here.
Guideline: Section I.B.14, I.C.4.b.1, I.C.21.c.3
Primary sources#
- ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027CMS — the source document for every page on this site (effective 1 Oct 2026)
- NCHS ICD-10-CM files — Tabular List, Index, POA exempt listOfficial code files, addenda and the list of codes exempt from POA reporting
- ICD-10 Coordination and Maintenance CommitteeWhere code proposals are debated; agendas, summaries and meeting materials
- CMS ICD-10 homeCode sets, transition guidance and Medicare coding policy
- AHA Coding ClinicOfficial coding advice from the AHA Central Office — subscription required
- HHS OIG Work PlanActive audit topics — useful for prioritising internal coding audits
- MEDESUN Medical Coding AcademyTraining, credential preparation and audit services by the author