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E83.42

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🧬 ICD-10-CM E83.42 — Hypomagnesemia

Billable Code Confirmed

ICD-10-CM E83.42 is a valid, billable 5-character ICD-10-CM code for FY2025. The code structure is: E83 (category — Disorders of mineral metabolism) + .4 (subcategory — Disorders of magnesium metabolism) + 2 (5th character — Hypomagnesemia). No 6th or 7th character is required. This code is valid for claims submission from October 1, 2024 through September 30, 2025.

Non-Billable Parent Codes — Never Submit These

  • ❌ E83.4 — 4-character subcategory header — missing the specific condition character; not billable
  • ❌ E83 — 3-character category — no additional specificity; not billable

Always submit E83.42 (all 5 characters) when the provider has documented hypomagnesemia as a confirmed diagnosis.

Critical Distinction: E83.42 vs. E61.2 — Metabolic vs. Dietary Deficiency

E83.42 (Hypomagnesemia) and E61.2 (Magnesium deficiency) are NOT interchangeable. The ICD-10-CM Tabular List places an Excludes1 note at the E83 category level excluding dietary mineral deficiency (E58-E61). This means:

  • E83.42 = Pathological/metabolic hypomagnesemia — low serum magnesium due to GI losses, renal wasting, medications, redistribution, or intrinsic metabolic disorders
  • E61.2 = Dietary magnesium deficiency — insufficient dietary intake without a systemic metabolic disorder

These two codes cannot be used together on the same claim. Documentation of the mechanism helps distinguish them — but when the provider simply writes “hypomagnesemia,” E83.42 is the correct selection. If the provider explicitly documents “dietary magnesium deficiency” with no underlying metabolic cause, E61.2 applies instead.

Additionally: Never use E83.42 for a neonate. Neonatal hypomagnesemia is coded with P71.2 (Neonatal hypomagnesemia) — listed as an Excludes1 condition for E83.42.

🔍 Code Description

ICD-10-CM E83.42 classifies hypomagnesemia — an abnormally low concentration of magnesium in the serum or blood, generally defined as a serum magnesium level below 1.7-1.8 mg/dL (0.7-0.75 mmol/L), though reference ranges vary slightly by laboratory. Magnesium is the second most abundant intracellular cation and is essential for over 300 enzymatic reactions, including ATP synthesis, DNA replication, protein synthesis, neuromuscular transmission, and cardiac automaticity.

Hypomagnesemia is one of the most common electrolyte abnormalities encountered in hospitalized patients (estimated prevalence 10-20%) and outpatient populations on long-term medications. It is frequently asymptomatic at mild levels (1.2-1.7 mg/dL) but becomes clinically dangerous as levels fall below 1.2 mg/dL (severe), producing neuromuscular, cardiovascular, and metabolic complications.

Common etiologies mapped to E83.42 (document the cause as an additional code when known):

  • Gastrointestinal losses: Malabsorption syndromes, chronic diarrhea, Crohn’s disease, short bowel syndrome, PPI-induced hypomagnesemia (T47.1X5A or Y43.3 for adverse effect of PPI)
  • Renal magnesium wasting: Gitelman syndrome, Bartter syndrome, loop and thiazide diuretics (code adverse effect), aminoglycoside nephrotoxicity, cisplatin nephrotoxicity, calcineurin inhibitors (tacrolimus, cyclosporine)
  • Nutritional/redistributive: Chronic alcoholism (F10.10-F10.99), refeeding syndrome, prolonged NPO status, total parenteral nutrition deficiency
  • Endocrine/metabolic: Hyperaldosteronism (E26.09, E26.1), hyperthyroidism (E05.xx), poorly controlled diabetes mellitus with glycosuria (Mg lost with glucose osmotic diuresis), hungry bone syndrome post-parathyroidectomy
  • Post-acute illness: Pancreatitis (K85.xx) — saponification sequesters Mg; sepsis with massive fluid resuscitation

Note

Hypomagnesemia is a “gateway” electrolyte disorder. It is the primary driver of treatment-refractory hypokalemia — potassium cannot be adequately repleted without first correcting magnesium deficiency. Similarly, hypocalcemia (E83.51) frequently co-occurs with hypomagnesemia because Mg is required for PTH secretion and action. Always evaluate and code all co-existing electrolyte abnormalities when documented.

🌳 Code Tree / Hierarchy

E83  Disorders of mineral metabolism ❌ Non-billable
│
├── E83.0  Disorders of copper metabolism (Wilson's disease) ❌ Non-billable
│
├── E83.1  Disorders of iron metabolism (hemochromatosis) ❌ Non-billable
│
├── E83.2  Disorders of zinc metabolism ❌ Non-billable
│
├── E83.3  Disorders of phosphorus metabolism and phosphatases ❌ Non-billable
│
├── E83.4  Disorders of magnesium metabolism ❌ Non-billable header
│   │
│   ├── E83.40  Disorders of magnesium metabolism, unspecified ✅ Billable
│   ├── E83.41  Hypermagnesemia ✅ Billable
│   ├── E83.42  HYPOMAGNESEMIA ◀ THIS CODE ✅ Billable
│   └── E83.49  Other disorders of magnesium metabolism ✅ Billable
│         (includes familial primary hypomagnesemia with hypercalciuria
│          and nephrocalcinosis; Gitelman syndrome if coder-confirmed)
│
├── E83.5  Disorders of calcium metabolism ❌ Non-billable header
│   ├── E83.50  Unspecified disorder of calcium metabolism ✅ Billable
│   ├── E83.51  Hypocalcemia ✅ Billable (frequently co-occurs with E83.42)
│   ├── E83.52  Hypercalcemia ✅ Billable
│   └── E83.59  Other disorders of calcium metabolism ✅ Billable
│
├── E83.8  Other disorders of mineral metabolism ❌ Non-billable header
│   └── E83.89  Other disorders of mineral metabolism ✅ Billable
│
└── E83.9  Disorder of mineral metabolism, unspecified ✅ Billable
           (Avoid — use specific subcategory code when available)

✅ Includes

The following clinical terms, documentation phrases, and clinical scenarios map to E83.42:

  • Hypomagnesemia (any cause, in non-neonatal patients) — including primary, secondary, iatrogenic, and drug-induced
  • Low serum magnesium / Serum magnesium deficiency
  • Renal magnesium wasting (without a more specific hereditary code — see E83.49 for Gitelman)
  • Medication-induced hypomagnesemia (PPI, diuretic, calcineurin inhibitor, cisplatin) — code E83.42 as the manifestation; add adverse effect or underdosing code for the causative drug
  • Alcoholism-related hypomagnesemia (code the alcohol use disorder separately)
  • Hypomagnesemia complicating pancreatitis (code pancreatitis as principal or additional)
  • Hypomagnesemia in malabsorption (code the GI condition separately)
  • Hypomagnesemia complicating diabetes mellitus (code the DM separately)

❌ Excludes

Excludes1 — Cannot be coded together with E83.42

The Excludes1 notes at the E83 category level prohibit coding the following conditions alongside any E83.x code — they represent distinct, separately classified entities that are incompatible with the E83 mechanism:

  • Dietary mineral deficiency (E61.2 — Magnesium deficiency) — when the provider explicitly documents dietary/nutritional cause only, without a systemic metabolic disorder; E83.42 and E61.2 are mutually exclusive per Excludes1
  • Parathyroid disorders (E20-E21) — code the parathyroid disorder instead when it is the primary cause of the metabolic disturbance
  • Vitamin D deficiency (E55.9, E55.0) — code vitamin D deficiency separately; do not use an E83.x code in its place

At the E83.42 code level:

  • Neonatal hypomagnesemia (P71.2) — listed as Excludes1; if the patient is a neonate, use P71.2 exclusively; E83.42 is for non-neonatal patients only

Excludes2 — Can be coded together if both are present

  • Disorders of fluid, electrolyte, and acid-base balance (E87.x) — including hypokalemia (E87.6), hyponatremia (E87.1), etc.; these are Excludes2 at the broader metabolic chapter level, meaning E83.42 and E87.6 (hypokalemia) CAN and SHOULD both be coded when both conditions are documented and clinically managed
  • Hypocalcemia (E83.51) — can be coded alongside E83.42 when documented, since both are often present simultaneously and require separate clinical management
  • Malnutrition codes (E40-E46) — reportable alongside E83.42 when co-documented; malnutrition is itself an HCC-bearing condition and should always be captured

🛠️ CPT Procedural Crosswalk — wRVU & Assistant Payable Status

The following CPT and HCPCS codes are most commonly associated with the diagnosis and treatment of E83.42. IV magnesium replacement is the mainstay of treatment for moderate-to-severe hypomagnesemia; oral supplementation does not typically generate a billable infusion code.

CPT / HCPCSDescriptionwRVU (Facility)Asst. Surgeon Payable?Co-Surgeon Payable?
96365Intravenous infusion, therapeutic/prophylactic/diagnostic; initial, up to 1 hour0.17❌ No❌ No
96366IV infusion, each additional hour (add-on to 96365)0.10❌ No❌ No
J3475Injection, magnesium sulfate, per 500 mg — report units based on total dose administered (e.g., 4 g = 8 units of J3475)N/A (drug)N/AN/A
83735Magnesium (Mg) — serum, plasma, or urine; the primary diagnostic and monitoring lab test0.00 (lab)N/AN/A
80048Basic Metabolic Panel — includes calcium, CO2, chloride, creatinine, glucose, potassium, sodium, BUN; does not include magnesium; order separately0.00 (lab)N/AN/A
80053Comprehensive Metabolic Panel — also does not include magnesium; 83735 must still be ordered separately0.00 (lab)N/AN/A
93000Electrocardiogram, routine ECG with at least 12 leads; with interpretation and report — critical for monitoring QTc prolongation, arrhythmia, and torsades de pointes risk0.17❌ No❌ No
99291Critical care, evaluation and management; first 30-74 minutes — for severe hypomagnesemia with arrhythmia, seizures, or cardiovascular instability4.50❌ No❌ No
99292Critical care; each additional 30 minutes (add-on to 99291)2.25❌ No❌ No

⚠️ Lab Coding Note: Magnesium (83735) is NOT included in the Basic Metabolic Panel (80048) or Comprehensive Metabolic Panel (80053). It must be ordered and billed separately. This is a commonly missed revenue opportunity — ensure magnesium replacement therapy is always linked to a documented serum magnesium level (83735) in the medical record.

⚠️ Drug Billing Note: J3475 (Magnesium sulfate injection, per 500 mg) must be reported with the correct number of units based on total dose. Standard IV magnesium sulfate doses:

  • Mild-moderate hypomagnesemia: 1-2 g IV = 2-4 units of J3475
  • Severe hypomagnesemia/arrhythmia: 4-8 g IV = 8-16 units of J3475
  • Eclampsia/pre-eclampsia (separate indication): 4-6 g loading + 1-2 g/hr maintenance — see O14.xx codes for that context Always report the J-code on the same claim line as 96365; append -JW or -JZ for wastage attestation per CR 13056 (effective 7/1/2023).

💊 Coding Scenarios

Scenario 1 — Hypomagnesemia with Refractory Hypokalemia, Inpatient

Clinical Vignette: A 67-year-old male with a history of CHF on furosemide is admitted for hypokalemia (K+ 2.8 mEq/L) unresponsive to 3 days of IV potassium supplementation. Repeat labs show serum magnesium of 1.1 mg/dL. The attending documents hypomagnesemia as the cause of refractory hypokalemia; both conditions are actively managed with IV magnesium sulfate 4 g and continued IV potassium replacement.

CPT / HCPCS Codes:

  • 96365 — IV infusion initial hour (magnesium sulfate)
  • 96366 — Each additional hour of infusion
  • J3475 × 8 — Magnesium sulfate, 4 grams total (8 × 500 mg)
  • 83735 — Serum magnesium level (diagnostic and monitoring)
  • 80048 — Basic Metabolic Panel (monitoring electrolytes including K+)

ICD-10-CM:

  • Principal Dx: E87.6 — Hypokalemia (reason for admission after study)
  • Secondary Dx: E83.42 — Hypomagnesemia (the underlying cause of refractory hypokalemia, clinically managed)
  • Secondary Dx: I50.9 — Heart failure, unspecified (comorbidity, contributing condition)

🏥 Inpatient Coder Tip: The principal diagnosis is the condition chiefly responsible for the admission after study — here, hypokalemia (E87.6) drove the admission, while E83.42 was identified as the cause. Sequence hypokalemia first. I50.9 should be captured as a secondary diagnosis for accurate DRG weighting; heart failure is commonly an MCC and can elevate DRG 641 → DRG 640.

Scenario 2 — PPI-Induced Hypomagnesemia, Outpatient

Clinical Vignette: A 71-year-old female on long-term omeprazole for GERD presents to her primary care physician with fatigue, muscle cramps, and tremors for 6 weeks. Labs show serum Mg 1.2 mg/dL. The physician documents “hypomagnesemia, adverse effect of omeprazole (PPI).” She is started on oral magnesium oxide and omeprazole is switched to an H2 blocker.

CPT / HCPCS Codes:

  • 99214 — Office visit, moderate medical decision making
  • 83735 — Serum magnesium level

ICD-10-CM:

  • E83.42 — Hypomagnesemia (the confirmed diagnosis)
  • T47.1X5A — Adverse effect of other antacids and anti-gastric-secretion drugs, initial encounter (PPI adverse effect — code the adverse effect of the causative drug as an additional code)
  • K21.0 — Gastro-esophageal reflux disease with esophagitis (the underlying indication for the PPI)

🏥 Outpatient Coder Tip: When hypomagnesemia is documented as an adverse effect of a correctly administered medication (PPI, diuretic, calcineurin inhibitor), code E83.42 first (the manifestation), then the adverse effect code from the Table of Drugs and Chemicals (T36-T65 with 5th character “5” = adverse effect). Do NOT use “poisoning” characters (1-4) for an adverse effect of a correctly prescribed drug. The adverse effect code links the hypomagnesemia to its drug cause, supporting medical necessity and clinical accuracy.

Scenario 3 — Hypomagnesemia with Hypocalcemia in Alcoholic Patient

Clinical Vignette: A 55-year-old male with alcohol use disorder is admitted with weakness, tetany, and numbness. Labs: Mg 0.9 mg/dL (critical), Ca 7.2 mg/dL (low), K+ 3.0 mEq/L (low). The attending documents hypomagnesemia, secondary hypocalcemia, hypokalemia, and alcohol dependence. IV magnesium sulfate 6 g + calcium gluconate + IV potassium are administered.

CPT / HCPCS Codes:

  • 96365 — IV infusion initial hour
  • 96366 × 2 — Additional hours (3-hour total infusion)
  • J3475 × 12 — Magnesium sulfate 6 g (12 × 500 mg units)
  • 83735 — Serum magnesium
  • 80048 — BMP (calcium, potassium, creatinine monitoring)
  • 93000 — EKG (QTc monitoring for arrhythmia risk)

ICD-10-CM:

  • Principal Dx: E83.42 — Hypomagnesemia (the condition chiefly responsible for this admission after study, with critical Mg level and tetany)
  • Secondary Dx: E83.51 — Hypocalcemia (co-occurring, caused by low Mg impairing PTH)
  • Secondary Dx: E87.6 — Hypokalemia (co-occurring electrolyte abnormality)
  • Secondary Dx: F10.20 — Alcohol dependence, uncomplicated (underlying etiology)

🏥 Inpatient Coder Tip: When multiple electrolyte abnormalities are present and managed, code each one separately — E83.42, E83.51, and E87.6 are all separately billable ICD-10-CM codes and should all appear on the UB-04 when documented and clinically managed. Do NOT collapse them into a single unspecified “electrolyte disorder” code (E87.8). Capturing all three improves DRG accuracy and reflects true clinical complexity. F10.20 adds important comorbidity context; document the relationship between alcohol use and the metabolic disturbances.

Scenario 4 — CDI Query: E83.42 vs. Abnormal Lab Result

Clinical Vignette: A coder reviews a hospitalized patient’s chart. The magnesium lab value of 1.5 mg/dL appears in the results. The nursing note says “ordered Mg replacement per protocol.” However, the physician’s progress note does not mention hypomagnesemia — only “electrolyte management per nursing protocol” is documented.

Action / Outcome:

The coder should NOT assign E83.42 based on the abnormal lab value and nursing action alone. Per ICD-10-CM Official Guidelines for Coding and Reporting (Section III — Additional Diagnoses): abnormal test results and signs/symptoms do not qualify as secondary diagnoses unless the attending physician has documented the condition in the diagnosis, assessment/plan, or discharge summary.

Correct Action: Submit a CDI (Clinical Documentation Integrity) query to the attending asking: “The patient’s serum magnesium was 1.5 mg/dL with magnesium replacement initiated. Would you please document whether hypomagnesemia is a confirmed diagnosis that was clinically managed during this encounter?”

If physician confirms: Code E83.42 as a secondary diagnosis, capturing the clinical management. If physician responds “incidental lab finding, not clinically significant”: Do not code E83.42.

⚠️ Coding Pitfalls and Tips

Pitfall or Tip
❌Do not code E83.42 from a lab value alone. ICD-10-CM requires a physician-documented diagnosis — “hypomagnesemia,” “low magnesium,” or “magnesium deficiency” must appear in the provider’s documentation (progress note, assessment/plan, or discharge summary) before E83.42 can be assigned
❌Do not confuse E83.42 with E61.2 (Magnesium deficiency — dietary). These are Excludes1 at the E83 category level — they are mutually exclusive. If the provider documents purely dietary/nutritional cause, E61.2 applies. If pathological low serum Mg is documented without specifying a dietary cause, E83.42 is correct
❌Do not use E83.42 for neonates. Neonatal hypomagnesemia is coded with P71.2 — listed as an Excludes1 condition; E83.42 is reserved for non-neonatal patients
❌Do not code E83.42 as principal diagnosis when a more clinically relevant condition drove the admission. For example, if a patient is admitted for sepsis with incidental hypomagnesemia found and treated, sepsis (A41.xx) is principal — E83.42 is secondary
❌Do not collapse multiple electrolyte disorders into one unspecified code. Code E83.42, E87.6 (hypokalemia), and E83.51 (hypocalcemia) separately when all are documented and managed — each provides distinct clinical and reimbursement information
✅Always code the underlying cause when documented. If hypomagnesemia is due to PPI use, code the adverse effect (T47.1X5A); if due to diuretics, code the adverse effect; if due to alcohol dependence, code F10.20-F10.99. Underlying etiology codes provide clinical specificity and support CDI programs
✅Always capture co-existing HCC-bearing conditions. E83.42 itself has no HCC weight — but malnutrition (E41-E46), alcoholic liver disease (K70.xx), heart failure (I50.xx), and CKD (N18.xx) frequently co-occur and must be separately captured for accurate risk adjustment
✅Report magnesium as a separate lab order (83735). It is NOT included in the BMP (80048) or CMP (80053). This is both a clinical safety point and a billing accuracy point — ensure the lab charge for 83735 is accurately captured whenever serum magnesium is ordered
✅Document magnesium levels in mg/dL AND mmol/L when possible. Different facilities use different units; clear documentation prevents coding uncertainty and facilitates accurate sequencing of severity

📚 Sources

  1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2025. Tabular List — E83.42 Hypomagnesemia; Section I.C.4 — Endocrine, Nutritional, and Metabolic Diseases; Section III — Reporting Additional Diagnoses.

  2. World Health Organization / CMS. ICD-10-CM Tabular List of Diseases and Injuries, FY2025 Release. Category E83 — Disorders of mineral metabolism; Excludes1 and Excludes2 notes.

  3. Centers for Medicare & Medicaid Services. MS-DRG v41 (FY2025) Definitions Manual. MDC 10 — Endocrine, Nutritional and Metabolic Diseases & Disorders; DRG 640-641.

  4. CMS. Billing and Coding: Serum Magnesium (A57198). Guidance on 83735 and associated ICD-10-CM indications.

  5. CMS CR 13056. JW/JZ Modifier Requirements for Medicare Part B Drug Claims. Effective July 1, 2023 — applicable to J3475 and all Part B drug code billing.

  6. American Medical Association (AMA). CPT 2024/2025 Professional Edition. Infusion therapy codes 96365-96366; pathology/laboratory codes 83735, 80048, 80053.

  7. ProvidersCare Billing / HealthSure Hub / PROMBS. Hypomagnesemia ICD-10 Code E83.42 — Diagnosis and Billing Guides. 2025-2026 coding reference articles.

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