2026 ICD-10-CM Diagnosis Code E21.0Primary hyperparathyroidism

ICD-10-CM Codes›E00–E89›E20-E35›E21

ICD-10-CM E21.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

E21.0 is a billable ICD-10-CM diagnosis code for primary hyperparathyroidism. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 643 through 645. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified endocrine disorders.

Code Identity

ICD-10-CM Code
E21.0
Billable Status
Yes — Valid for Submission
Code Describes
Primary hyperparathyroidism
Short Description
Primary hyperparathyroidism
Same as the full description in the CMS dataset.
Parent Code
E21
Hyperparathyroidism and other disorders of parathyroid gland

Code Classification

ChapterE00–E89Endocrine, nutritional and metabolic diseases
SectionE20-E35Disorders of other endocrine glands
CategoryE21Hyperparathyroidism and other disorders of parathyroid gland
This CodeE21.0Primary hyperparathyroidism

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Familial hyperparathyroidism
  • Familial isolated hyperparathyroidism
  • Hyperparathyroidism-jaw tumor syndrome
  • Neonatal hyperparathyroidism
  • Neonatal severe primary hyperparathyroidism
  • Nephropathy, deafness, hyperparathyroidism syndrome
  • Normocalcemic primary hyperparathyroidism
  • Osteitis fibrosa cystica
  • Parathyroid hyperplasia
  • Primary hyperparathyroidism
  • Primary water-clear cell hyperplasia

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

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

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Curvature
      • spine (acquired) (angular) (idiopathic) (incorrect) (postural)
        • due to or associated with
          • osteitis
            • fibrosa cystica
    • Disease, diseased
      • osteofibrocystic
    • Enlargement, enlarged
      • parathyroid (gland)
    • Hyperparathyroidism
      • primary
    • Hyperplasia, hyperplastic
      • parathyroid (gland)
    • Hypertrophy, hypertrophic
      • parathyroid (gland)
    • Osteitis
      • fibrosa NEC
        • cystica (generalisata)
    • Osteitis
      • fibrosa NEC
        • osteoplastica
    • Osteitis
      • parathyroid
    • Recklinghausen disease
      • bones
    • Von Recklinghausen
      • disease (neurofibromatosis)
        • bones

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR END015
Other specified and unspecified endocrine disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Osteitis Fibrosa Cystica

    a fibrous degeneration, cyst formation, and the presence of fibrous nodules in bone, usually due to hyperparathyroidism.

  • Hyperparathyroidism

    a condition of abnormally elevated output of parathyroid hormone (or pth) triggering responses that increase blood calcium. it is characterized by hypercalcemia and bone resorption, eventually leading to bone diseases. primary hyperparathyroidism is caused by parathyroid hyperplasia or parathyroid neoplasms. secondary hyperparathyroidism is increased pth secretion in response to hypocalcemia, usually caused by chronic kidney diseases.

  • Neonatal Severe Primary Hyperparathyroidism

    an autosomal recessive form of kenny-caffey syndrome that is secondary to mutation(s) in the tcbe gene that encodes tubulin-specific chaperone e; it is characterized by the following: hypoparathyroidism with hypocalcemia, marked growth retardation, craniofacial anomalies, absent diploic space, cortical thickening and medullary stenosis of long bones, and small hands and feet.

  • Primary Hyperparathyroidism

    hyperfunction of the parathyroid glands resulting in the overproduction of parathyroid hormone. it is caused by parathyroid adenoma, parathyroid hyperplasia, parathyroid carcinoma, and multiple endocrine neoplasia. it is associated with hypercalcemia and hypophosphatemia. signs and symptoms include weakness, fatigue, nausea, vomiting, constipation, depression, bone pain, osteoporosis, cystic bone lesions, and kidney stones.

  • Neonatal Severe Primary Hyperparathyroidism

    a genetic condition caused by loss-of-function mutation(s) in the casr gene, encoding extracellular calcium-sensing receptor. it is characterized by severe hypercalcemia and metabolic bone disease occurring in the first six months of life.

Patient EducationClinical

Parathyroid Disorders

Most people have four pea-sized glands, called parathyroid glands, on the thyroid gland in the neck. Though their names are similar, the thyroid and parathyroid glands are completely different. The parathyroid glands make parathyroid hormone (PTH), which helps your body keep the right balance of calcium and phosphorous.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert E21.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
252.01 Primary hyperparathyroid
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About E21.0Overview

Is E21.0 (Hyperparathyroidism and other disorders of parathyroid gland) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report primary hyperparathyroidism on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does E21.0 group to?

When primary hyperparathyroidism is the principal diagnosis on an inpatient stay, it groups to MS-DRG 643, 644, 645, with relative weights from 0.7683 to 1.6461 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of E21.0?

Under the General Equivalence Mappings, primary hyperparathyroidism converts to ICD-9-CM 252.01 (primary hyperparathyroid). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.