Diabetes Mellitus - Inpatient Coding Reference

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🏥 Clinical Overview

Why does diabetes coding matter so much in inpatient PMR? Diabetes mellitus (DM) is the #1 underlying cause of lower extremity amputation in the United States. The vast majority of your amputee patients will carry a DM diagnosis. Beyond amputation, DM drives a cascade of complications — neuropathy, nephropathy, retinopathy, peripheral vascular disease, autonomic dysfunction — all of which are active, clinically managed comorbidities during an inpatient rehab stay. Coding DM accurately, with its complications, is critical for DRG CC/MCC capture, HCC risk adjustment, and supporting medical necessity.

The Core Coding Rule for DM

ICD-10-CM instructs: when a patient has DM AND a complication, assume a causal relationship and code them together as a combination code — UNLESS the physician explicitly states they are unrelated.

This is a significant departure from old ICD-9 logic. You do not need the physician to write “due to diabetes” for most DM complications. If the patient has DM and diabetic neuropathy, you code E11.40. The combination code does both jobs. You do not code E11 (DM alone) and then a separate neuropathy code.

Type 1 vs. Type 2 vs. Other — How to Tell

Type	Code Category	Key Clinical Clues
Type 1 (T1DM)	E10	Insulin-dependent since youth; C-peptide absent; absolute insulin requirement; often slender
Type 2 (T2DM)	E11	Most common; adult onset; often obese; may or may not use insulin
Drug/chemical-induced	E09	Caused by steroids, tacrolimus, antipsychotics, etc.
Due to underlying condition	E08	DM secondary to pancreatitis, Cushing’s, pancreatic cancer
Other specified	E13	Latent autoimmune DM in adults (LADA), post-pancreatectomy DM
Unspecified	E14	⚠️ Avoid — query for type

When insulin use is documented but type is unclear: E11 (Type 2) with an insulin use code (Z79.4) is the default when type is not specified. Type 2 patients commonly use insulin; insulin use alone does NOT make a patient Type 1. Query the physician if documentation is genuinely ambiguous.

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📋 E10 - Type 1 Diabetes Mellitus

Parent code E10 is not billable. Code to full specificity.

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E10 with Hyperosmolarity

Code	Description	CC/MCC	HCC
E10.00	T1DM with hyperosmolarity without nonketotic hyperglycemic-hyperosmolar coma (NKHHC)	MCC	HCC 17
E10.01	T1DM with hyperosmolarity with coma	MCC	HCC 17

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E10 with Ketoacidosis (DKA)

Code	Description	CC/MCC	HCC
E10.10	T1DM with ketoacidosis without coma	MCC	HCC 17
E10.11	T1DM with ketoacidosis with coma	MCC	HCC 17

DKA is a life-threatening complication almost exclusively seen in T1DM (though T2DM can have DKA under extreme stress). Documentation: anion gap metabolic acidosis, elevated serum ketones, blood glucose typically >250 mg/dL. DKA is an MCC — extremely important for DRG weight.

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E10 with Kidney Complications

Code	Description	CC/MCC	HCC
E10.21	T1DM with diabetic nephropathy	CC	HCC 19
E10.22	T1DM with diabetic chronic kidney disease, stage 1-2	CC	HCC 19
E10.23	T1DM with diabetic chronic kidney disease, stage 3a	CC	HCC 19
E10.24	T1DM with diabetic chronic kidney disease, stage 3b	CC	HCC 19
E10.25	T1DM with diabetic chronic kidney disease, stage 4	MCC	HCC 19
E10.26	T1DM with diabetic chronic kidney disease, stage 5	MCC	HCC 19
E10.29	T1DM with other diabetic kidney complication	CC	HCC 19

Combination code guidance: When coding E10.2x for CKD, you still add the CKD stage code (N18.1-N18.6) as an additional diagnosis per ICD-10 instructions. The E10.2x code tells you DM is the cause; the N18 code specifies the stage.

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E10 with Ophthalmic Complications

Code	Description	CC/MCC	HCC
E10.311	T1DM with unspecified diabetic retinopathy with macular edema	CC	HCC 19
E10.319	T1DM with unspecified diabetic retinopathy without macular edema	—	HCC 19
E10.321	T1DM with mild nonproliferative retinopathy with macular edema, right eye	CC	HCC 19
E10.329	T1DM with mild nonproliferative retinopathy without macular edema, right eye	—	HCC 19
E10.341	T1DM with severe nonproliferative retinopathy with macular edema, right eye	CC	HCC 19
E10.351	T1DM with proliferative retinopathy with macular edema, right eye	CC	HCC 19
E10.36	T1DM with diabetic cataract	—	HCC 19
E10.37X1	T1DM with diabetic macular degeneration, right eye	CC	HCC 19
E10.39	T1DM with other diabetic ophthalmic complication	—	HCC 19

⚠️ Ophthalmic DM codes are laterality-specific in many categories. Always capture laterality (right, left, bilateral) from the documentation. In your Ophthalmology specialty work, you will see these frequently.

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E10 with Neurological Complications

Code	Description	CC/MCC	HCC
E10.40	T1DM with diabetic neuropathy, unspecified	CC	HCC 18
E10.41	T1DM with diabetic mononeuropathy	CC	HCC 18
E10.42	T1DM with diabetic polyneuropathy	CC	HCC 18
E10.43	T1DM with diabetic autonomic (poly)neuropathy	CC	HCC 18
E10.44	T1DM with diabetic amyotrophy	CC	HCC 18
E10.49	T1DM with other diabetic neurological complication	CC	HCC 18

Diabetic neuropathy in the PMR world: In amputee patients, diabetic polyneuropathy (E10.42 or E11.42) is extremely common and is a significant secondary diagnosis during rehab. It affects sensation, balance, and prosthetic tolerance. Always code when documented.

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E10 with Peripheral Circulatory / Vascular Complications

Code	Description	CC/MCC	HCC
E10.51	T1DM with diabetic peripheral angiopathy without gangrene	CC	HCC 18
E10.52	T1DM with diabetic peripheral angiopathy with gangrene	MCC	HCC 18
E10.59	T1DM with other circulatory complications	CC	HCC 18

E10.52 / E11.52 — these are MCCs and HCC-18. When the patient’s foot gangrene led to amputation, keep coding this even after the amputation. The underlying peripheral angiopathy with gangrene (even as a historical condition now post-amputation) is what drove the admission.

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E10 with Other / Combination Complications

Code	Description	CC/MCC	HCC
E10.610	T1DM with diabetic neuropathic arthropathy	CC	HCC 18
E10.618	T1DM with other diabetic arthropathy	CC	HCC 18
E10.620	T1DM with diabetic dermatitis	—	HCC 18
E10.621	T1DM with foot ulcer	CC	HCC 18
E10.622	T1DM with other skin ulcer	CC	HCC 18
E10.628	T1DM with other skin complications	—	HCC 18
E10.630	T1DM with periodontal disease	—	HCC 18
E10.641	T1DM with hypoglycemia with coma	MCC	HCC 17
E10.649	T1DM with hypoglycemia without coma	CC	HCC 17
E10.65	T1DM with hyperglycemia	—	—
E10.69	T1DM with other specified complication	—	HCC 18
E10.8	T1DM with unspecified complications	—	HCC 18
E10.9	T1DM without complications	—	HCC 35

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📋 E11 - Type 2 Diabetes Mellitus

Parent code E11 is not billable. The E11 family mirrors E10 in structure. The most common codes in the inpatient PMR amputee population are listed below with full detail.

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E11 with Hyperosmolarity

Code	Description	CC/MCC	HCC
E11.00	T2DM with hyperosmolarity without NKHHC	MCC	HCC 17
E11.01	T2DM with hyperosmolarity with coma	MCC	HCC 17

Hyperosmolar Hyperglycemic State (HHS) is the T2DM equivalent of DKA — severe hyperglycemia without significant ketoacidosis. Blood glucose often exceeds 600 mg/dL. This is an MCC and inpatient emergency.

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E11 with Ketoacidosis

Code	Description	CC/MCC	HCC
E11.10	T2DM with ketoacidosis without coma	MCC	HCC 17
E11.11	T2DM with ketoacidosis with coma	MCC	HCC 17

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E11 with Kidney Complications

Code	Description	CC/MCC	HCC
E11.21	T2DM with diabetic nephropathy	CC	HCC 19
E11.22	T2DM with diabetic chronic kidney disease, stage 1-2	CC	HCC 19
E11.23	T2DM with diabetic CKD, stage 3a	CC	HCC 19
E11.24	T2DM with diabetic CKD, stage 3b	CC	HCC 19
E11.25	T2DM with diabetic CKD, stage 4	MCC	HCC 19
E11.26	T2DM with diabetic CKD, stage 5	MCC	HCC 19
E11.29	T2DM with other diabetic kidney complication	CC	HCC 19

📌 Always add N18.1-N18.6 as additional code per ICD-10 instructional notes when coding E11.2x. This is a required secondary code.

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E11 with Neurological Complications

Code	Description	CC/MCC	HCC
E11.40	T2DM with diabetic neuropathy, unspecified	CC	HCC 18
E11.41	T2DM with diabetic mononeuropathy	CC	HCC 18
E11.42	T2DM with diabetic polyneuropathy	CC	HCC 18
E11.43	T2DM with diabetic autonomic (poly)neuropathy	CC	HCC 18
E11.44	T2DM with diabetic amyotrophy	CC	HCC 18
E11.49	T2DM with other diabetic neurological complication	CC	HCC 18

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E11 with Peripheral Vascular / Circulatory Complications

Code	Description	CC/MCC	HCC
E11.51	T2DM with diabetic peripheral angiopathy without gangrene	CC	HCC 18
E11.52	T2DM with diabetic peripheral angiopathy with gangrene	MCC	HCC 18
E11.59	T2DM with other circulatory complications	CC	HCC 18

E11.51 and E11.52 are the most critical codes in the PMR amputee population. They represent the vascular disease that destroyed the foot and led to amputation. Code these even after the amputation has been completed — the underlying angiopathy is still active and being managed with anticoagulation, wound surveillance, and cardiovascular risk reduction.

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E11 with Ophthalmic Complications

Code	Description	CC/MCC	HCC
E11.311	T2DM with unspecified diabetic retinopathy with macular edema	CC	HCC 19
E11.319	T2DM with unspecified diabetic retinopathy without macular edema	—	HCC 19
E11.3411	T2DM with severe nonproliferative retinopathy with macular edema, right eye	CC	HCC 19
E11.3412	T2DM with severe nonproliferative retinopathy with macular edema, left eye	CC	HCC 19
E11.3413	T2DM with severe nonproliferative retinopathy with macular edema, bilateral	CC	HCC 19
E11.351	T2DM with proliferative retinopathy with macular edema, right eye	CC	HCC 19
E11.36	T2DM with diabetic cataract	—	HCC 19
E11.39	T2DM with other diabetic ophthalmic complication	—	HCC 19

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E11 with Other/Combination Complications

Code	Description	CC/MCC	HCC
E11.610	T2DM with diabetic neuropathic arthropathy	CC	HCC 18
E11.618	T2DM with other diabetic arthropathy	CC	HCC 18
E11.620	T2DM with diabetic dermatitis	—	HCC 18
E11.621	T2DM with diabetic foot ulcer	CC	HCC 18
E11.622	T2DM with other skin ulcer	CC	HCC 18
E11.628	T2DM with other skin complications	—	HCC 18
E11.630	T2DM with periodontal disease	—	HCC 18
E11.641	T2DM with hypoglycemia with coma	MCC	HCC 17
E11.649	T2DM with hypoglycemia without coma	CC	HCC 17
E11.65	T2DM with hyperglycemia	—	—
E11.69	T2DM with other specified complication	—	HCC 18
E11.8	T2DM with unspecified complications	—	HCC 18
E11.9	T2DM without complications	—	HCC 36

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🏷️ Critical Secondary Codes — Always Consider

Code	Description	When to Add
Z79.4	Long-term current use of insulin	T2DM patient using insulin — does NOT change type; add as additional
Z79.84	Long-term current use of oral hypoglycemic drugs	T2DM on metformin, glipizide, etc.
Z79.85	Long-term current use of injectable non-insulin antidiabetic drugs	GLP-1 agonists (semaglutide, liraglutide), SGLT2 inhibitors
N18.1	CKD, Stage 1	Add when E11.22 is coded
N18.2	CKD, Stage 2	Add when E11.22 is coded
N18.31	CKD, Stage 3a	Add when E11.23 is coded
N18.32	CKD, Stage 3b	Add when E11.24 is coded
N18.4	CKD, Stage 4	Add when E11.25 is coded
N18.5	CKD, Stage 5	Add when E11.26 is coded — add Z99.2 if on dialysis
Z99.2	Dependence on renal dialysis	Add when patient is on hemodialysis or peritoneal dialysis
E87.65	Hypomagnesemia	Commonly seen in T2DM — impacts glycemic control
R73.01	Impaired fasting glucose	Pre-diabetes (not DM)
R73.09	Other abnormal glucose	Glucose intolerance NOS

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🧠 HCC Mapping Summary - Diabetes (CMS-HCC v28)

HCC	Conditions Included	Key DM Codes	Risk Impact
HCC 17	DM with acute complications (DKA, HHS, hypoglycemia with coma)	E11.00, E11.10, E11.641	Highest DM HCC
HCC 18	DM with chronic complications (neuropathy, PVD, skin/joint)	E11.40-E11.59, E11.621	Very common in PMR amputee
HCC 19	DM with ophthalmic/renal complications	E11.21-E11.39	Important in diabetic nephropathy
HCC 35	T1DM without complications	E10.9	Lower weight
HCC 36	T2DM without complications	E11.9	Lowest DM HCC — avoid if complications documented

Coding Imperative: HCC 36 (T2DM without complications) is worth far less in risk adjustment than HCC 18 (T2DM with complications). If your patient has T2DM AND peripheral neuropathy AND foot ulcer, you should be coding E11.40 and/or E11.621 — not E11.9. Always capture the complication combination codes.

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💊 Coding Scenarios

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Scenario 1: T2DM — Post-BKA Rehab, Polyneuropathy, Peripheral Angiopathy

Clinical Story: A 69-year-old male with T2DM on insulin admitted to PMR following right below-knee amputation secondary to gangrenous diabetic foot disease. He also has documented diabetic polyneuropathy affecting bilateral lower extremities and CKD Stage 3b. PMR physician documents management of DM, adjustment of insulin regimen, and monitoring of renal function.

DM-Related Codes (all additional diagnoses under Z47.81 principal):

• E11.52 — T2DM with diabetic peripheral angiopathy with gangrene (the etiology of the amputation — gang code even post-amputation)
• E11.42 — T2DM with diabetic polyneuropathy (documented, affecting rehab tolerance and sensation)
• E11.24 — T2DM with diabetic CKD, stage 3b (combination code)
• N18.32 — CKD, Stage 3b (required additional code per ICD-10)
• Z79.4 — Long-term use of insulin (T2DM patient using insulin)

DRG Impact: E11.52 is MCC → DRG 945; E11.42 and E11.24 are CCs — all captured appropriately.

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Scenario 2: T2DM with Hypoglycemic Episode During PMR Admission

Clinical Story: A 74-year-old female T2DM patient on insulin is in inpatient PMR following left AKA. On Day 3, nursing documents a blood glucose of 42 mg/dL with confusion and diaphoresis. The PMR physician evaluates the patient, administers dextrose, and adjusts the insulin regimen. The patient returns to baseline. No coma occurred.

DM Code for this event:

• E11.649 — T2DM with hypoglycemia without coma (confusion and diaphoresis do not constitute coma — physician documents resolution with treatment)
• Z79.4 — Long-term use of insulin

HCC and DRG note: E11.649 is a CC, elevating the DRG if not already captured. It also maps to HCC 17 (acute DM complication) — an important capture for risk adjustment.

Query tip: If the physician documents “hypoglycemic encephalopathy” or “loss of consciousness,” escalate to E11.641 (with coma) — that is an MCC.

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Scenario 3: T2DM Without Documentation of Complications — Query Opportunity

Clinical Story: A chart review shows: patient has T2DM. PMR daily notes document monitoring of blood glucose, insulin administration, wound surveillance of residual limb, evaluation of sensation in the contralateral foot (noting decreased sensation), and foot inspection. No complication of diabetes is explicitly named.

Coding as-is: E11.9 — T2DM without complications → HCC 36 only

Query opportunity: The physician is monitoring and managing sensation loss in the contralateral foot and performing wound surveillance — clinical indicators of diabetic neuropathy and/or circulatory involvement. A physician query asking whether the patient has diabetic polyneuropathy or diabetic peripheral angiopathy, based on the clinical findings, is appropriate and can shift the code from E11.9 to E11.42 (CC, HCC 18) or E11.51 (CC, HCC 18).

Never assume or code without physician documentation — but recognize when the clinical picture supports a query.

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⚠️ Common Coding Pitfalls - Diabetes

1. Coding E11.9 when complications are documented — This is the single biggest missed capture opportunity. Scan the entire record for neuropathy, nephropathy, retinopathy, PVD, foot ulcer, autonomic dysfunction.

2. Not adding Z79.4 for insulin-using T2DM — Insulin use by a T2DM patient must be captured with Z79.4. Omitting it creates a misleading picture of the patient’s disease management.

3. Confusing E11.65 (hyperglycemia) with DKA/HHS — E11.65 is for elevated blood glucose without a crisis. DKA and HHS are separate, more severe codes.

4. Failing to add N18.xx when coding E11.2x — ICD-10 instructs you to add an additional code from N18 to identify the stage. This is not optional.

5. Coding E11 AND a separate neuropathy code — Incorrect. The combination code (e.g., E11.42) already captures both DM and polyneuropathy. Do not also code G62.9 (polyneuropathy NOS) alongside it.

6. Not querying when type is unspecified — Always query the physician if chart documentation uses phrases like “insulin-dependent diabetes” without specifying type. Document findings before defaulting to E11.

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🔗 Related Notes

• Z47.81 — Orthopedic aftercare, surgical amputation
• Z89.511 — Acquired absence of right leg below knee
• E11.51 — T2DM with peripheral angiopathy without gangrene
• E11.52 — T2DM with peripheral angiopathy with gangrene
• Peripheral Vascular Disease Coding Reference
• PMR Amputee Coding Reference
• Wound Care and Debridement CPT Reference

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Created: 2026-05-07 | MCW Inpatient Abstraction Team | Crystal | CIC-Prep Sources: ICD-10-CM FY2026, CMS-HCC v28 Mappings, ADA Clinical Standards of Care 2026