2025 ICD-10-CM Diagnosis Code E21.0

Approximate Synonyms

The following list of clinical terms are approximate synonyms, alternative descriptions, or common phrases that might be used by patients, healthcare providers, or medical coders to describe the same condition. These synonyms and related diagnosis terms are often used when searching for an ICD-10 code, especially when the exact medical terminology is unclear. Whether you're looking for lay terms, similar diagnosis names, or common language alternatives, this list can help guide you to the correct ICD-10 classification.

Clinical Classification

Clinical Classifications group individual ICD-10-CM diagnosis codes into broader, clinically meaningful categories. These categories help simplify complex data by organizing related conditions under common clinical themes.

They are especially useful for data analysis, reporting, and clinical decision-making. Even when diagnosis codes differ, similar conditions can be grouped together based on their clinical relevance. Each category is assigned a unique CCSR code that represents a specific clinical concept, often tied to a body system or medical specialty.

Clinical Information

• 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.

MS-DRG Mapping for ICD-10-CM Code E21.0

Diagnosis-Related Groups (DRGs) are used to classify hospital cases for billing and healthcare management. They help standardize how hospitals and other providers are reimbursed for inpatient care. Patients are grouped based on their principal diagnosis into broader categories called Major Diagnostic Categories (MDCs).

Once assigned to a DRG, the hospital receives a set payment for the patient’s care, regardless of the actual services provided. This fixed rate is intended to cover the typical cost of treating patients within that group. The payment amount depends on the DRG's relative weight, which reflects the expected complexity and cost of care based on the severity of the patient’s condition.

Diagnostic related groups encourage healthcare providers to focus on quality and efficiency in patient care while managing costs effectively. The diagnosis code is present in the following groups for version MS-DRG V42.0 applicable from 10/01/2024 through 09/30/2025.

Convert E21.0 to ICD-9-CM

Below are the ICD-9 codes that most closely match this ICD-10 code, based on the General Equivalence Mappings (GEMs). This ICD-10 to ICD-9 crosswalk tool is helpful for coders who need to reference legacy diagnosis codes for audits, historical claims, or approximate code comparisons.

Patient Education

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.

If your parathyroid glands make too much or too little hormone, it disrupts this balance. If they secrete extra PTH, you have hyperparathyroidism, and your blood calcium rises. In many cases, a benign tumor on a parathyroid gland makes it overactive. Or, the extra hormones can come from enlarged parathyroid glands. Very rarely, the cause is cancer.

If you do not have enough PTH, you have hypoparathyroidism. Your blood will have too little calcium and too much phosphorous. Causes include injury to the glands, endocrine disorders, or genetic conditions. Treatment is aimed at restoring the balance of calcium and phosphorous.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

[Learn More in MedlinePlus]

Familial isolated hyperparathyroidism

Familial isolated hyperparathyroidism is an inherited condition characterized by overactivity of the parathyroid glands (hyperparathyroidism). The four parathyroid glands are located in the neck, and they release a hormone called parathyroid hormone that regulates the amount of calcium in the blood. In familial isolated hyperparathyroidism, one or more overactive parathyroid glands release excess parathyroid hormone, which causes the levels of calcium in the blood to rise (hypercalcemia). Parathyroid hormone stimulates the removal of calcium from bone and the absorption of calcium from the diet, and the mineral is then released into the bloodstream.

In people with familial isolated hyperparathyroidism, the production of excess parathyroid hormone is caused by tumors that involve the parathyroid glands. Typically only one of the four parathyroid glands is affected, but in some people, more than one gland develops a tumor. The tumors are usually noncancerous (benign), in which case they are called adenomas. Rarely, people with familial isolated hyperparathyroidism develop a cancerous tumor called parathyroid carcinoma. Because the production of excess parathyroid hormone is caused by abnormalities of the parathyroid glands, familial isolated hyperparathyroidism is considered a form of primary hyperparathyroidism.

Disruption of the normal calcium balance resulting from overactive parathyroid glands causes many of the common signs and symptoms of familial isolated hyperparathyroidism, such as kidney stones, nausea, vomiting, high blood pressure (hypertension), weakness, and fatigue. Because calcium is removed from bones to be released into the bloodstream, hyperparathyroidism often causes thinning of the bones (osteoporosis). The age at which familial isolated hyperparathyroidism is diagnosed varies from childhood to adulthood. Often, the first indication of the condition is elevated calcium levels identified through a routine blood test, even though the affected individual may not yet have signs or symptoms of hyperparathyroidism or hypercalcemia.

[Learn More in MedlinePlus]

Primary Hyperparathyroidism

Describes symptoms, causes, and treatment of primary hyperparathyroidism where one or more enlarged parathyroid gland secretes too much parathyroid hormone.
[Learn More in MedlinePlus]

Code History

• FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
• FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
• FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
• FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
• FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
• FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
• FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
• FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
• FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.