ICD-10 Code for Hyponatremia

A sodium level of 133 mEq/L and a sodium level of 118 mEq/L both technically qualify as hyponatremia, but they’re not remotely the same clinical situation — one might not even need treatment, the other could be a hospital admission. ICD-10 doesn’t actually split E87.1 by severity the way the lab value might suggest; it’s a single code. What matters for coding purposes is documenting the severity and likely cause in the note itself, even though the code stays the same.

E87.1 covers both hypo-osmolality and hyponatremia together, and it’s billable as-is. The coding challenge with this diagnosis usually isn’t picking the wrong code — it’s under-documenting why the finding mattered enough to justify repeat labs, an inpatient stay, or a nephrology referral.

FY 2027 ICD-10-CM (CMS, eff. 10/1/2026) · CPT 2026 (AMA) · Last verified: October 2026

Quick Answer

E87.1

Hypo-osmolality and hyponatremia

E87.1 is billable and covers hyponatremia regardless of severity. Document the sodium level, severity, and suspected cause in the note — the code doesn’t change, but the supporting detail is what justifies the level of care billed.

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ICD-10 Code for Hyponatremia: Full Code List and Related Diagnoses

ICD-10 Code Description Billable
E87.1 MOST USED Hypo-osmolality and hyponatremia ✓
E87.0 Hyperosmolality and hypernatremia ✓
E22.2 Syndrome of inappropriate secretion of antidiuretic hormone ✓
E87.8 Other disorders of electrolyte and fluid balance, not elsewhere classified ✓
E86.0 Dehydration ✓

CPT Codes Commonly Billed With This Diagnosis

CPT Code Description Medicare Rate* Common Modifiers
80053 Comprehensive metabolic panel ~$11 -59
80048 Basic metabolic panel ~$8 -59
99214 Office visit, established patient, moderate complexity ~$136 -25
99223 Initial hospital inpatient visit, high complexity ~$156 -25
83930 Sodium, urine ~$7 -59

*Approximate 2026 CMS national non-facility rate. Lab test rates are from the 2026 CMS Clinical Laboratory Fee Schedule. Rates vary by geography, setting, and payer contract. Refer to the CMS Physician Fee Schedule for official rates.

Which Medical Specialty Handles This?

Mild, asymptomatic hyponatremia found incidentally on routine labs is usually managed entirely in primary care or internal medicine — recheck the level, look at medications, adjust as needed. It moves to nephrology once the case gets more complicated: a low sodium that doesn't correct with the obvious fixes, a suspected SIADH picture, or any case where the underlying cause isn't clear from the medication list and history alone. Severe or symptomatic hyponatremia is typically an inpatient admission rather than an outpatient visit.

Common Billing & Documentation Mistakes

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Severity Not Documented to Support the Level of Service Billed

A higher-level E&M code or hospital admission needs the note to reflect why hyponatremia rose to that level of complexity — the actual sodium value, symptoms, and clinical reasoning, not just the diagnosis code.

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Repeat Metabolic Panels Without a Documented Reason

Payers watch for repeat 80053/80048 orders in short succession. Each repeat needs a one-line reason in the note — 'rechecking after fluid restriction,' for example — not just a standing lab order.

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Underlying Cause Never Identified or Documented

Hyponatremia is almost always a sign of something else — medication effect, SIADH, heart failure, dehydration. A claim that only ever lists E87.1 without any documented workup toward a cause can look incomplete on review.

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Inpatient Admission Coded Without Severity Criteria Documented

If hyponatremia is the primary reason for admission, the note needs to clearly support why outpatient management wasn’t appropriate — symptom severity, sodium level, and rate of decline all matter here.

Coding Tips

  • Always document the actual sodium value and whether it’s acute or chronic — this single detail does more to justify the visit level than anything else in the note.
  • When ordering a repeat metabolic panel, note why — 'recheck post fluid restriction' or similar — rather than leaving repeat labs unexplained.
  • Document the suspected or confirmed underlying cause whenever possible — medication-induced, SIADH, dehydration — even a working theory strengthens the claim.
  • If the case escalates to inpatient care, make sure the admission note documents the sodium level and symptoms that made outpatient management inappropriate.

Frequently Asked Questions

What is the ICD-10 code for hyponatremia?

E87.1, which covers hyponatremia and hypo-osmolality together. There’s no severity-specific code — mild and severe hyponatremia both use E87.1, so severity needs to be documented in the note itself, not in the code.

Does the ICD-10 code change based on how low the sodium is?

No. E87.1 applies regardless of severity. What changes is the level of service billed for the visit and how much clinical detail the note needs to support that level.

What causes hyponatremia, and does that affect coding?

Common causes include SIADH (E22.2), dehydration (E86.0), and certain medications. If a cause is identified, coding it alongside E87.1 gives a fuller clinical picture and can better support the workup that was billed.

What lab CPT code is used to check sodium levels?

80048 (basic metabolic panel) or 80053 (comprehensive metabolic panel) both include sodium and are the standard codes for checking or rechecking levels.

How does OmniMD help document hyponatremia correctly?

OmniMD’s lab-result workflow flags abnormal sodium values directly in the chart and prompts for severity and suspected cause at the point of documentation, so the note supports whatever level of care ends up being billed.

Document Severity, Not Just the Diagnosis

OmniMD flags abnormal labs at the point of care and prompts for the detail that actually supports your billing.

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