Hypomagnesemia is an electrolyte disturbance characterized by abnormally low serum magnesium levels that can cause neuromuscular, cardiovascular, and metabolic complications. Accurate ICD-10 coding for hypomagnesemia supports clinical communication, medical necessity justification, quality measurement, and appropriate reimbursement.
Clinically, hypomagnesemia can be acute or chronic and may be primary or secondary to other conditions (e.g., diuretic use, alcoholism, malabsorption). Precise coding and documentation influence claim acceptance, audit defensibility, and care coordination. This guide explains what the ICD-10-CM code for hypomagnesemia represents, when to use or avoid it, related diagnosis codes, coding best practices to optimize reimbursement, and common billing pitfalls.
The ICD-10-CM Code for Hypomagnesemia is E83.42.
Hypomagnesemia is a disorder of magnesium metabolism defined by a serum magnesium concentration below the laboratory reference range, often with symptoms such as muscle weakness, tremors, seizures, arrhythmias, or refractory hypokalemia/calcium abnormalities. In ICD-10-CM classification, E83.42 designates the clinical diagnosis of decreased magnesium level when documented by the provider without further specification of cause. Use E83.42 when the medical record explicitly documents hypomagnesemia as a diagnosis or problem requiring evaluation or treatment.
Use E83.42 when a patient presents with an acute drop in serum magnesium documented by laboratory values and the clinician records hypomagnesemia as a diagnosis or primary clinical problem. Examples include emergency department evaluation for arrhythmia or seizure where laboratory confirmation supports treatment and the provider documents hypomagnesemia.
Assign E83.42 when hypomagnesemia is treated during an inpatient admission (for example, IV magnesium replacement or specific ordered monitoring) and the diagnosis is documented in the chart as a condition that affected care or length of stay.
Code E83.42 for ambulatory visits focused on management of confirmed low magnesium (e.g., ongoing oral supplementation, monitoring labs) when the documentation indicates hypomagnesemia as the reason for the visit or the problem being addressed.
Use E83.42 when hypomagnesemia is explicitly documented as contributing to another clinical issue (for example, hypomagnesemia contributing to refractory ventricular arrhythmia) and both conditions are reported with appropriate sequencing based on the encounter context.
Do not use E83.42 when the provider documents a specific causal condition that has its own ICD-10 code and is the primary diagnosis (for example, post-surgical malabsorption causing electrolyte disturbances). Instead, report the underlying cause code as primary and add E83.42 as a secondary code only when the provider documents hypomagnesemia as a separate, treated clinical problem.
Do not assign E83.42 based solely on an isolated low magnesium lab result if the clinician has not documented hypomagnesemia as a diagnosis or problem requiring evaluation or treatment. Coding requires provider documentation noting the clinical significance of the lab abnormality.
Avoid E83.42 when low magnesium is transient, expected, and not addressed (for example, a single low value with no follow-up, no treatment, and no diagnostic significance recorded). If the provider documents "transient hypomagnesemia" but provides no treatment or clinical plan, clarify intent before coding.
If the electrolyte disturbance is coded under a specific poisoning, toxicity, or metabolic syndrome that has a more appropriate primary code, do not use E83.42 as the principal diagnosis unless the provider documents hypomagnesemia as a separate treated condition.
| Condition | Code | When It Is Used | When It Is Not Used |
|---|---|---|---|
| Hypomagnesemia | E83.42 | When provider documents low serum magnesium as a diagnosis or problem requiring evaluation/treatment (acute symptomatic, inpatient treatment, outpatient management) | When only an isolated lab value is present without provider documentation or when a specific underlying cause is the primary diagnosis |
| Hypermagnesemia | E83.41 | When elevated serum magnesium is documented as a diagnosis requiring treatment or monitoring | Not used for low magnesium or when hypermagnesemia is only an incidental lab value without provider-documented significance |
| Hypocalcemia | E83.51 | When provider documents low serum calcium as a diagnosis requiring treatment or monitoring and clinical notes support the diagnosis | Not used for magnesium disorders; do not substitute for hypomagnesemia or use when only a lab result without documentation of a clinical problem |
| Hypokalemia | E87.6 | When provider documents low serum potassium causing symptoms or requiring intervention and it is the condition addressed during the encounter | Not used for magnesium disorders or when potassium abnormality is incidental without provider-documented diagnosis or treatment |
Ensure provider notes explicitly state "hypomagnesemia" with supporting clinical context (symptoms, treatment plan, lab values). Clear documentation ties the code to medical necessity and supports reimbursement.
Include serum magnesium values, reference ranges, collection dates, and trends in the medical record. Linking objective data to the documented diagnosis strengthens claim defense and justifies treatment-related charges.
Document treatments (IV/oral magnesium, cardiac monitoring, electrolyte panels) and indicate that these services were medically necessary because of hypomagnesemia. This supports appropriate coding and reimbursement for associated services.
Report primary and secondary diagnoses according to the encounter purpose. If hypomagnesemia is the reason for admission or visit, sequence E83.42 first; if it is secondary to another primary condition, sequence accordingly and include both codes with rationale in documentation.
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Coding for hypomagnesemia has direct impact on revenue cycle outcomes:
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Q1: What is the ICD-10 code for hypomagnesemia?
The ICD-10-CM code for hypomagnesemia is E83.42. Use this code when the provider documents hypomagnesemia as a diagnosis or problem supported by clinical findings or treatment.
Q2: When should I use E83.42 vs related codes?
Use E83.42 for documented low magnesium. Use related codes such as E83.41 for documented high magnesium, E83.51 for documented low calcium, or E87.6 for low potassium when those specific electrolyte disturbances are diagnosed and treated. Sequence codes based on the primary reason for the encounter and include secondary electrolyte codes when they contributed to care.
Q3: What documentation is required when coding for hypomagnesemia?
Document the diagnosis explicitly in the provider note, include lab values and reference ranges, describe symptoms or clinical effects, record treatments or monitoring performed, and note plans for follow-up. Link interventions directly to the diagnosis to demonstrate medical necessity.
Q4: What are common denial reasons when coding for hypomagnesemia?
Denials commonly arise from lack of provider documentation, coding based solely on lab results, incorrect diagnosis sequencing, and missing linkage between hypomagnesemia and billed services. See our guide on denial management for strategies to prevent and resolve denials.