What is ICD-10 code E21.0?

E21.0 is the ICD-10-CM diagnosis code for Primary hyperparathyroidism. Overactivity of the parathyroid glands due to an intrinsic problem with the glands themselves, causing elevated calcium levels in the blood. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E21.0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E21.0 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. E21.0 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. E21.0 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for E21.0?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. E21.0 was a payment HCC under V24 (Other Significant Endocrine and Metabolic Disorders) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting E21.0?

Ensure the hyperparathyroidism is primary (gland dysfunction) and not secondary to kidney disease or vitamin D deficiency Document whether adenoma, hyperplasia, or carcinoma is present if known Because E21.0 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM E21.0: Primary hyperparathyroidism

ICD-10-CM Code View

HCC Buddy Code Card

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Code lookupE21.0Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Disorders of other endocrine glands (E20-E35)

E21.0

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Primary hyperparathyroidism

Overactivity of the parathyroid glands due to an intrinsic problem with the glands themselves, causing elevated calcium levels in the blood.

Buddy Insight

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.194

ACA/HHS

Mapped

HCC 30

HHS-HCC 30

Varies by metal level

ESRD/PACE

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.036

RXHCC

Mapped

HCC 43

Other Significant Endocrine a...

RAF 0.063

Code Book Path

Official

E21Hyperparathyroidism and other disorders of parathyroid gland

E21.0Primary hyperparathyroidism

Inclusion Terms

Official

Hyperplasia of parathyroid
Osteitis fibrosa cystica generalisata [von Recklinghausen's disease of bone]

Excludes 2

Official

familial hypocalciuric hypercalcemia (E83.52)

Related Child Codes

Official

E21.1Secondary hyperparathyroidism, not elsewhere classified

E21.2Other hyperparathyroidism

E21.3Hyperparathyroidism, unspecified

E21.4Other specified disorders of parathyroid gland

E21.5Disorder of parathyroid gland, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E21.0 in this effective period.

Excludes 1

Official

adult osteomalacia (M83.-)
ectopic hyperparathyroidism (E34.2)
hungry bone syndrome (E83.81)
infantile and juvenile osteomalacia (E55.0)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E21.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E21.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E21.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Document the underlying etiology (adenoma, hyperplasia, or carcinoma), serum calcium and parathyroid hormone levels, presence of end-organ damage (kidney stones, bone density loss), and current treatment plan including surgical status.

MEAT Support

HCC Buddy guidance

Audit Caution

HCC Buddy guidance

Do not assign E21.0 when hyperparathyroidism is secondary to chronic kidney disease or vitamin D deficiency; those require E21.

Ensure the provider explicitly documents 'primary' hyperparathyroidism rather than assuming based on elevated calcium alone.

Common Mistakes

HCC Buddy guidance

E21.1 (secondary hyperparathyroidism due to another condition like chronic kidney disease), E21.3 (hyperparathyroidism unspecified when type is not determined), E83.52 (hypercalcemia which is a lab finding, not the underlying disorder).

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is E21.0 an HCC code?

Yes. E21.0 maps to Other Significant Endocrine and Metabolic Disorders under the V24 model but is not retained in V28.

Code: E21.0
Description: Primary hyperparathyroidism
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 23, Other Significant Endocrine and Metabolic Disorders

0.194

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

0.036

RxHCCHCC 43, Other Significant Endocrine and Metabolic Disorders

0.063

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work E21.0 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E21.0

For E21.0 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed E21.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E21.0 is the ICD-10-CM diagnosis code for primary hyperparathyroidism. Overactivity of the parathyroid glands due to an intrinsic problem with the glands themselves, causing elevated calcium levels in the blood. E21.0 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering disorders of other endocrine glands (e20-e35).

Under the older CMS-HCC V24 model, E21.0 maps to Other Significant Endocrine and Metabolic Disorders (HCC 23) with a community, non-dual, aged base RAF weight of 0.194. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Ensure the hyperparathyroidism is primary (gland dysfunction) and not secondary to kidney disease or vitamin D deficiency. Because E21.0 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for E21.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Ensure the hyperparathyroidism is primary (gland dysfunction) and not secondary to kidney disease or vitamin D deficiency
•Document whether adenoma, hyperplasia, or carcinoma is present if known

Clinical Significance

Primary hyperparathyroidism results from autonomous overproduction of parathyroid hormone, most commonly due to a parathyroid adenoma, leading to hypercalcemia with serious skeletal, renal, and cardiovascular consequences. Left untreated, chronic hypercalcemia accelerates osteoporosis, nephrolithiasis, and increases cardiovascular mortality risk.

Documentation Requirements

✓Document the underlying etiology (adenoma, hyperplasia, or carcinoma), serum calcium and parathyroid hormone levels, presence of end-organ damage (kidney stones, bone density loss), and current treatment plan including surgical status.

Commonly Confused Codes

•E21.1 (secondary hyperparathyroidism due to another condition like chronic kidney disease), E21.3 (hyperparathyroidism unspecified when type is not determined), E83.52 (hypercalcemia which is a lab finding, not the underlying disorder).