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E87.1ICD-10-CM

Hypo-osmolality and hyponatremia

BillableSIADH is an Excludes1No severity or acuity axis

How the code is built

E

Chapter

Endocrine, nutritional and metabolic diseases

87

Category

Other disorders of fluid, electrolyte and acid-base balance

1

Char 4

Hypo-osmolality and hyponatremia

Chapter

E00 to E89

Endocrine, nutritional and metabolic diseases

Block

E70 to E88

Metabolic disorders

Category

E87

Other disorders of fluid, electrolyte and acid-base balance

Billable

Yes

Complete at 4 characters

Inclusion term

Sodium deficiency

Salt depletion and low salt syndrome are classified here

Excludes1 at E87.1

SIADH (E22.2)

The two are never reported together

DefinitionCode structureClinical pictureDocumentationDecision guideTabular listComparisonClaim contextDenialsSources

Key takeaways

  • E87.1 codes hyponatremia and hypo-osmolality together, in a single code covering both states
  • Sodium deficiency, salt depletion, and low salt syndrome all classify here
  • SIADH carries an Excludes1 at this code, so E87.1 and E22.2 never appear on the same claim
  • The code carries no severity and no acuity, so mild and severe and acute and chronic all report identically
  • It is billable, and inpatient reporting turns on whether the record shows the condition was evaluated or treated
1Definition

What ICD-10 code E87.1 means

E87.1 is the ICD-10-CM code for hypo-osmolality and hyponatremia. It applies when a provider documents a low serum sodium, a low serum osmolality, or both, since the classification treats them as one code rather than two.

Sodium deficiency is the inclusion term, and the Alphabetic Index routes a wide set of everyday phrases here, including salt depletion, low salt syndrome, sodium depletion, and sick cell syndrome. What the code does not carry is severity, acuity, or cause. A sodium of 132 documented as mild and chronic and a sodium of 115 documented as acute and symptomatic report to the same four characters.

Code

E87.1

Descriptor

Hypo-osmolality and hyponatremia

Chapter

Endocrine, nutritional and metabolic diseases

Block

Metabolic disorders

Category

E87, other disorders of fluid, electrolyte and acid-base balance

Billable

Yes

Inclusion term

Sodium deficiency

Excludes1 at E87.1

Syndrome of inappropriate secretion of antidiuretic hormone (E22.2)

The descriptor has not changed in any fiscal year since 2015. The exposure on this code is not a retired reference, and it is not a missing subcode. One of the leading causes of hyponatremia has its own code and an Excludes1 note that forbids reporting both.

2Code structure

One code for two states, and a cause question that decides everything

E87.1 has no subdivisions. Two structural facts determine whether it is correct, and neither one is about anatomy.

What the single code absorbs

Hyponatremia

E87.1

Hypo-osmolality

E87.1

Both together

E87.1 once, not twice

Mild, moderate, or severe

E87.1, with no severity character

Acute or chronic

E87.1, with no acuity character

Because severity never reaches the code, the clinical seriousness of the episode lives entirely in the documentation and in the other codes reported alongside it. That is worth knowing before assuming the code understates a case.

Whether the cause replaces the code or joins it

SIADH

E22.2 replaces E87.1, per the Excludes1

Diabetes insipidus

E23.2 replaces it, per the category Excludes1

Hyperemesis gravidarum, or ectopic or molar pregnancy

The obstetric code replaces it, per the category Excludes1

Newborn

The perinatal chapter code replaces it, per the chapter Excludes1

Heart failure, cirrhosis, or kidney disease

Both are reported, since no exclusion applies

A medication such as a thiazide or an SSRI

E87.1 with the adverse effect code

Volume depletion or dehydration

Both are reported, since E86.- is a separate condition

This is the split that decides most E87.1 claims. Four causes have exclusion notes that displace the code entirely. Everything else coexists with it.

3Clinical picture

Clinical findings documented under E87.1

A record supporting this code pairs a laboratory finding with a provider statement that the finding is a diagnosis.

Laboratory

Serum sodium below the reference range, with serum and urine osmolality where measured

General

Fatigue, weakness, headache, reduced appetite

Gastrointestinal

Nausea and vomiting

Neuromuscular

Muscle cramps, salt-depletion cramps, unsteadiness

Neurologic

Confusion, lethargy, altered mental status, seizures in severe cases

Volume status

Documented as hypovolemic, euvolemic, or hypervolemic, which points toward the cause

Volume status is the finding that most often unlocks a better code. A record documenting euvolemic hyponatremia with concentrated urine is describing the picture that leads to a SIADH diagnosis, and a SIADH diagnosis moves the encounter to E22.2 entirely.

4Documentation

What the chart must show

  • A provider-stated diagnosis of hyponatremia, since the value alone is a laboratory finding.
  • The serum sodium result and any osmolality studies performed
  • Volume status, documented explicitly
  • The suspected or confirmed cause, including any medication contributing to it
  • Whether the condition is acute or chronic, and whether it is symptomatic
  • The evaluation performed, including additional laboratory studies ordered because of the finding
  • The treatment given, whether fluid restriction, sodium replacement, or a medication change
  • Monitoring, including repeat testing and any increase in observation

Inpatient reporting turns on a rule separate from anything in the tabular list. A secondary diagnosis is reportable when it required clinical evaluation, therapeutic treatment, diagnostic studies, an extended stay, or increased nursing care and monitoring. A borderline sodium noted in a results table and never addressed meets none of those, and the Official Guidelines direct that abnormal findings are not coded unless the provider indicates their clinical significance.

That rule matters more here than on most codes, because hyponatremia contributes to inpatient severity classification. A code that raises the weight of a stay and rests on an unaddressed laboratory value is exactly the pattern payer audits look for.

5Decision guide

When to assign E87.1, and when not to

Hyponatremia, no cause named

E87.1

Hypo-osmolality

E87.1

Sodium deficiency, salt depletion, or low salt syndrome

E87.1

Hyponatremia due to SIADH

E22.2 alone, never with E87.1

Hyponatremia with diabetes insipidus

E23.2, per the category Excludes1

Hyponatremia with hyperemesis gravidarum

The obstetric code, per the category Excludes1

Hyponatremia in a newborn

The perinatal chapter code

Hyponatremia from a thiazide, SSRI, or other drug

E87.1 with the adverse effect code

Hyponatremia in heart failure or cirrhosis

Both conditions, since neither excludes the other

Dehydration or volume depletion, with or without low sodium

E86.-, plus E87.1 when hyponatremia is separately documented

Hypernatremia

E87.0

Low sodium on labs, with no diagnosis stated

Query, since a finding is not a diagnosis

There is no sequencing rule attached to E87.1. The question is whether an exclusion displaces it, and if not, whether the record supports reporting it at all.

Query rather than default when the note documents euvolemia with concentrated urine, names a medication known to cause hyponatremia, or records a sodium result the assessment never mentions.

6Tabular list

Instructional notes at E87.1 and above

Inclusion term at E87.1

Sodium deficiency

Excludes1 at E87.1

Syndrome of inappropriate secretion of antidiuretic hormone (E22.2)

Excludes1 at E87

Diabetes insipidus (E23.2), electrolyte imbalance associated with hyperemesis gravidarum (O21.1), electrolyte imbalance following ectopic or molar pregnancy (O08.5), familial periodic paralysis (G72.3), metabolic acidemia in newborn unspecified (P19.9)

Excludes1 at E70 to E88

Congenital adrenal hyperplasia (E25.0), Marfan syndrome (Q87.4-), androgen insensitivity syndrome (E34.5-), and others

Excludes1 at E00 to E89

Transitory endocrine and metabolic disorders specific to newborn (P70 to P74)

Every note attached to this code is an Excludes1, which means every one of them is a prohibition rather than a permission. That is unusual, and it changes how a coder should read the category.

The SIADH note carries the most weight. Reporting E87.1 and E22.2 together is prohibited outright, and the reason is that SIADH is defined by the hyponatremia it produces. When the provider names SIADH as the diagnosis, E22.2 already carries the low sodium, and E87.1 adds nothing but a code-pair conflict.

The newborn exclusion works the same way at the chapter level. Hyponatremia in a newborn is not an E87.1 case at all, since the perinatal chapter classifies transitory metabolic disorders specific to the newborn.

7Comparison

Codes frequently confused with E87.1

E22.2

Descriptor

Syndrome of inappropriate secretion of antidiuretic hormone

Use instead when

SIADH is documented, which excludes E87.1

E87.0

Descriptor

Hyperosmolality and hypernatremia

Use instead when

Sodium is elevated rather than reduced

E87.5, E87.6

Descriptor

Hyperkalemia and hypokalemia

Use instead when

The abnormality is potassium, reportable alongside E87.1

E87.2-

Descriptor

Acidosis, subdivided into acute and chronic metabolic acidosis and other

Use instead when

An acid-base disorder is documented

E87.3

Descriptor

Alkalosis

Use instead when

An alkalotic state is documented

E87.4

Descriptor

Mixed disorder of acid-base balance

Use instead when

More than one acid-base disturbance is documented

E87.7

Descriptor

Fluid overload

Use instead when

Volume excess is the diagnosis

E86.0

Descriptor

Dehydration

Use instead when

Dehydration is documented, reportable alongside E87.1

E86.1

Descriptor

Hypovolemia

Use instead when

Volume depletion is documented

E86.9

Descriptor

Volume depletion, unspecified

Use instead when

Volume depletion is documented without further detail

E23.2

Descriptor

Diabetes insipidus

Use instead when

Diabetes insipidus is documented, which the category Excludes1 blocks

O21.1

Descriptor

Hyperemesis gravidarum with metabolic disturbance

Use instead when

Electrolyte imbalance accompanies hyperemesis

G72.3

Descriptor

Familial periodic paralysis

Use instead when

The disorder is the familial periodic paralysis itself

P70 to P74

Descriptor

Transitory endocrine and metabolic disorders specific to newborn

Use instead when

The patient is a newborn

The E86 relationship is the one worth stating plainly. Volume depletion and hyponatremia are different conditions; they carry no exclusion against each other, and a patient who is both dehydrated and hyponatremic is correctly reported with a code from each. Dropping one because they feel related loses a diagnosis the record supports.

8Claim context

Services commonly reported with E87.1

E87.1 appears across every setting. It supports emergency department and inpatient evaluation and management, the basic and comprehensive metabolic panels that identify and track it, serum and urine osmolality studies, urine sodium testing, and the intravenous fluid or medication administration used to treat it.

The inpatient stakes are higher than the outpatient ones. Hyponatremia contributes to severity classification for an admission, which means it affects payment for the stay and therefore attracts review. What auditors examine is not the code but the record behind it, asking whether the low sodium was evaluated, treated, or monitored, or merely present in a results table.

On the outpatient side, repeat metabolic panels tracking a chronic low sodium need documentation connecting each test to a clinical question. Confirm the applicable local coverage determination before submitting serial testing.

9Denials

Coding errors that cause denials

Reporting E87.1 alongside E22.2 for SIADH

Report E22.2 alone, since the Excludes1 prohibits the pair

Coding E87.1 from a sodium result the provider never addressed

Query, since abnormal findings are not coded without stated clinical significance

Reporting E87.1 twice for hyponatremia and hypo-osmolality

Report the code once, since it covers both

Coding E87.1 for a newborn

Assign the perinatal chapter code

Coding E87.1 with diabetes insipidus or hyperemesis gravidarum

Assign the excluded condition's code instead

Dropping E86.0 because hyponatremia is already coded

Report both, since dehydration and hyponatremia are separate conditions

Missing the adverse effect code when a drug caused the hyponatremia

Add the adverse effect code alongside E87.1

Reporting E87.1 as a secondary diagnosis on an inpatient stay with no evaluation or treatment documented

Report only when the condition met the reporting criteria for other diagnoses

10Sources

Where to verify E87.1

ICD-10-CM Official Guidelines for Coding and Reporting

The rule on abnormal findings and clinical significance, and the criteria for reporting other diagnoses

The ICD-10-CM Tabular List at E87, E86, and E22

The Excludes1 at E87.1, the category and chapter exclusions, and the SIADH classification

The CMS ICD-10 code page

Current code files and the annual addenda

Medicare Coverage Database

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Last reviewed August 2026

This page is a free reference for billing and coding teams and is not coding, legal, or clinical advice. Code selection depends on the documentation in the record and on the policy of the payer being billed. Verify every code, instructional note, and sequencing rule against the current ICD-10-CM files and the Official Guidelines for Coding and Reporting for the applicable date of service. ICD-10-CM is maintained by the CDC's National Center for Health Statistics and published by CMS. CPT is a registered trademark of the American Medical Association. TruCare is not affiliated with CMS, NCHS, the AHA, or the AMA.

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