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E83.42ICD-10-CM

Hypomagnesemia

BillableThree Excludes1 conditions sit above itA second low-magnesium code exists and cannot be paired with it

How the code is built

E

Chapter

Endocrine, nutritional and metabolic diseases

83

Category

Disorders of mineral metabolism

4

Char 4

Disorders of magnesium metabolism

2

Char 5

Low, rather than high or other

Chapter

E00 to E89

Endocrine, nutritional and metabolic diseases

Block

E70 to E88

Metabolic disorders

Category

E83

Disorders of mineral metabolism

Subcategory

E83.4

Disorders of magnesium metabolism

Billable

Yes

Complete at 5 characters

Inclusion terms

None

The code line carries no Applicable To entries

Excludes1 at E83

Dietary mineral deficiency, parathyroid disorders, vitamin D deficiency

All three inherited, none on the code line

DefinitionCode structureClinical pictureDocumentationDecision guideTabular listComparisonClaim contextDenialsSources

Key takeaways

  • E83.42 codes hypomagnesemia as a disorder of mineral metabolism
  • A separate code for magnesium deficiency sits in the nutritional deficiency block, and the two are mutually exclusive
  • Vitamin D deficiency and parathyroid disorders are both Excludes1 above this code
  • The code carries no severity and no acuity, so every degree of low magnesium reports identically
  • It is billable, and its most valuable use is as a companion code that routinely gets dropped
1Definition

What ICD-10 code E83.42 means

E83.42 is the ICD-10-CM code for hypomagnesemia. It applies when a provider documents a low serum magnesium as a disorder of mineral metabolism.

The code carries no inclusion terms and no notes on its own line. Everything constraining it sits at the category above, and what sits there is unusually consequential.

Code

E83.42

Descriptor

Hypomagnesemia

Chapter

Endocrine, nutritional and metabolic diseases

Block

Metabolic disorders

Category

E83, disorders of mineral metabolism

Subcategory

E83.4, disorders of magnesium metabolism

Billable

Yes

Inclusion terms

None at the code line

Excludes1 at E83

Dietary mineral deficiency (E58 to E61), parathyroid disorders (E20 to E21), vitamin D deficiency (E55.-)

ICD-10-CM has two codes for low magnesium, and they cannot be reported together. E83.42 classifies it as a metabolic disorder. A separate code in the nutritional deficiency block classifies magnesium deficiency as a nutritional problem. Each category carries an Excludes1 note naming the other, so the prohibition runs in both directions.

That is the single most important fact about this code, and published guidance gets it wrong. A billing guide dated within the last month advises that when hypomagnesemia is nutritional, a coder may need the nutritional code in addition to E83.42. The tabular list prohibits that pairing from both sides. One code or the other, never both.

2Code structure

A direction axis, and a fork the coder has to choose

E83.42 has no subdivisions. The fifth character records direction and nothing else.

The direction axis within magnesium metabolism

Magnesium disorder, direction not stated

E83.40

High magnesium

E83.41

Low magnesium

E83.42

This code

Another magnesium disorder

E83.49

The fork that sits outside the category

A metabolic derangement, including renal magnesium wasting and hereditary tubular disorders

E83.42

A nutritional deficiency from inadequate intake or malabsorption

The magnesium deficiency code in the nutritional block

The two are mutually exclusive by Excludes1, so this is a genuine fork rather than a choice of emphasis. The classification asks whether the low magnesium is being reported as a metabolic disorder or as a nutritional deficiency, and it does not permit hedging.

One asymmetry between the two branches matters for drug-related cases. The nutritional deficiency category carries an explicit instruction to add an adverse effect code identifying the drug. The mineral metabolism category does not. Since proton pump inhibitors, loop and thiazide diuretics, aminoglycosides, amphotericin, cisplatin, and calcineurin inhibitors are all recognised causes of magnesium loss, that difference shapes how a drug-related case gets built. Where the branch is genuinely unclear, query before assigning either code.

What the code does not record

Serum magnesium value

None

Mild, moderate or severe

None

Acute or chronic

None

Renal versus gastrointestinal loss

None directly, though named tubular disorders have their own codes

Symptomatic or asymptomatic

None

3Clinical picture

Clinical findings documented under E83.42

A record supporting this code pairs a low magnesium result with a provider statement making it a diagnosis.

Laboratory

Serum magnesium below the reference range, with potassium and calcium where measured

Neuromuscular

Tremor, muscle cramps, weakness, tetany, hyperreflexia

Cardiac

Palpitations, arrhythmia, and electrocardiographic changes

Neurologic

Irritability, confusion, seizures in severe depletion

Source of loss

Diarrhea, vomiting, malabsorption, alcohol use, renal wasting, medication effects

Companion abnormalities

Coexisting hypokalemia and hypocalcemia

The companion row is the one that changes what gets reported. Magnesium depletion impairs both potassium retention and parathyroid function, so a patient with hypomagnesemia frequently has low potassium and low calcium as well. Each has its own code, and none is prohibited alongside this one.

4Documentation

What the chart must show

  • A provider-stated diagnosis, since the value alone is a laboratory finding
  • Whether the low magnesium is framed as a metabolic disorder or a nutritional deficiency
  • The serum magnesium result, with potassium and calcium where obtained
  • The route of loss, whether gastrointestinal, renal, or reduced intake
  • Medications contributing to it, named individually
  • Any named underlying disorder, such as a renal tubular condition
  • Coexisting electrolyte abnormalities, documented separately so each can be reported
  • Treatment given, whether oral or intravenous replacement, and the monitoring plan

The metabolic-versus-nutritional framing is the element most often missing, and it is the one the classification most needs. A note recording low magnesium in a patient with short bowel syndrome and a note recording one in a patient with renal wasting look similar in the laboratory section and point to different chapters.

5Decision guide

When to assign E83.42, and when not to

Hypomagnesemia, framed as a metabolic disorder

E83.42

Low magnesium, no framing offered

E83.42, or query where a nutritional cause is documented

Magnesium deficiency from inadequate intake or malabsorption

The nutritional deficiency code; never with E83.42

Hypermagnesemia

E83.41

Magnesium disorder, direction not stated

E83.40

Hypomagnesemia with hypokalemia

E83.42 and E87.6

Hypomagnesemia with hypocalcemia

E83.42 and E83.51

Vitamin D deficiency

E55.-, never with an E83 code

A parathyroid disorder

E20 to E21, never with an E83 code

Bartter's syndrome

E26.81

Hypomagnesemia from a documented drug

The applicable code with the adverse effect code, following the branch the documentation supports

A low magnesium value with no diagnosis stated

Query, since a laboratory finding is not a diagnosis

There is no sequencing rule attached to E83.42. The questions are which branch the documentation supports, whether an inherited Excludes1 displaces the code, and whether the companion electrolyte codes have been reported.

Query rather than default when the note frames the deficiency nutritionally, when a contributing medication is present but unlinked, and when a magnesium value sits in the labs with no comment in the assessment.

6Tabular list

Instructional notes above E83.42

Excludes1 at E83

Dietary mineral deficiency (E58 to E61)

Excludes1 at E83

Parathyroid disorders (E20 to E21)

Excludes1 at E83

Vitamin D deficiency (E55.-)

Excludes1 at E58 to E61

Disorders of mineral metabolism (E83.-), pointing back at this code

Use additional at E58 to E61

An adverse effect code identifying the drug, where applicable

Excludes1 at E70 to E88

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

All three prohibitions reaching E83.42 are inherited from the category. A coder verifying the code entry alone sees a descriptor and nothing else.

Two of the three run against conditions that genuinely co-occur with low magnesium, which is where the difficulty lies.

Magnesium is required for parathyroid hormone secretion and action, so hypomagnesemia produces functional hypoparathyroidism. The classification nevertheless prohibits reporting an E83 code with a parathyroid disorder code.

Magnesium is also required for vitamin D activation, and the two deficiencies travel together clinically. The classification prohibits that pairing too. Vitamin D deficiency and hypomagnesemia cannot appear on the same claim, which is counterintuitive enough that it is worth checking against your edits before assuming a rejection was a system error.

The dietary mineral exclusion is reciprocal, and that is what creates the fork described above. Each category names the other.

7Comparison

Codes frequently confused with E83.42

E83.40

Descriptor

Disorders of magnesium metabolism, unspecified

Use instead when

A magnesium disorder is documented without direction

E83.41

Descriptor

Hypermagnesemia

Use instead when

Magnesium is elevated

E83.49

Descriptor

Other disorders of magnesium metabolism

Use instead when

Another named magnesium disorder is documented

E61.2

Descriptor

Magnesium deficiency

Use instead when

The deficiency is framed as nutritional, which the reciprocal Excludes1 separates from E83.42

E83.51, E83.52

Descriptor

Hypocalcemia and hypercalcemia

Use instead when

Calcium is abnormal, reportable alongside

E83.50, E83.59

Descriptor

Unspecified and other disorders of calcium metabolism

Use instead when

A calcium disorder is documented

E87.6, E87.5

Descriptor

Hypokalemia and hyperkalemia

Use instead when

Potassium is abnormal, reportable alongside

E87.1, E87.0

Descriptor

Hypo-osmolality and hyponatremia, hyperosmolality and hypernatremia

Use instead when

Sodium is abnormal, reportable alongside

E83.81

Descriptor

Hungry bone syndrome

Use instead when

Post-parathyroidectomy mineral shift is documented

E83.9

Descriptor

Disorder of mineral metabolism, unspecified

Use instead when

A mineral disorder is documented without further detail

E55.-

Descriptor

Vitamin D deficiency

Use instead when

Vitamin D deficiency is documented, which the Excludes1 blocks

E20.-, E21.-

Descriptor

Hypoparathyroidism and hyperparathyroidism

Use instead when

A parathyroid disorder is documented, which the Excludes1 blocks

E26.81

Descriptor

Bartter's syndrome

Use instead when

Bartter's syndrome is documented as the underlying cause

E58 to E61

Descriptor

Dietary calcium, selenium, zinc, and other mineral deficiencies

Use instead when

Another nutritional mineral deficiency is documented

The E61.2 row is the one to read twice. Both codes describe low magnesium. Secondary references frequently describe the nutritional code using the word hypomagnesemia, which is precisely why coders reach for both. The classification permits only one.

8Claim context

Services commonly reported with E83.42

E83.42 supports evaluation and management across primary care, hospital medicine, nephrology and oncology, along with the laboratory monitoring and replacement therapy that follow.

Magnesium testing is not among the twenty-three national laboratory determinations, so frequency and indication rules are set contractor by contractor. Serial magnesium levels during a replacement course are ordinary care, but the record needs to connect each draw to a clinical question rather than an interval habit.

Intravenous magnesium administration, whether by infusion or as a piggyback with other therapy, is reported with its own administration codes and carries its own documentation requirements. Contractor policy on infusion services and on repeat electrolyte testing is where the variation sits.

The most valuable role this code plays is as a companion. Hypomagnesemia frequently accompanies hypokalemia and hypocalcemia, and neither of those carries an exclusion against it. A chart documenting all three supports three codes, and the second and third are the ones routinely dropped. On an inpatient claim, that omission understates the metabolic picture of the stay.

9Denials

Coding errors that cause denials

Reporting E83.42 and the nutritional magnesium deficiency code together

Choose one, since each category excludes the other

Reporting E83.42 with a vitamin D deficiency code

Choose one, since the Excludes1 at E83 prohibits the pair

Reporting E83.42 with a parathyroid disorder code

Choose one, since the Excludes1 at E83 prohibits the pair

Coding E83.42 from a magnesium value the provider never addressed

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

Dropping the hypokalemia or hypocalcemia code

Report each, since none is prohibited alongside

Omitting the adverse effect code in a drug-related case

Add it, following the branch the documentation supports

Searching for a severity or acuity character

Report E83.42, since neither exists

Assigning E83.40 when the record states the magnesium is low

Assign E83.42

Billing serial magnesium testing with no documented reason

Record the replacement course and the clinical question behind each draw

10Sources

Where to verify E83.42

ICD-10-CM Official Guidelines for Coding and Reporting

The Excludes1 definition, the rule on abnormal findings and clinical significance, and the adverse effect coding convention

ICD-10-CM Tabular List at E83 and at E58 to E61

The three Excludes1 notes at E83, the reciprocal Excludes1 in the nutritional deficiency block, and the adverse effect instruction that appears in only one of them

CMS ICD-10 code page and the FY 2026 files

Current code files and the annual addenda

Laboratory NCD list

Confirms magnesium testing is not among the twenty-three national laboratory policies, so coverage is contractor-specific

Medicare Coverage Database

Search your contractor's determinations for electrolyte testing frequency and infusion administration.

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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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