3 Electrolyte Interpretation and Priorities

Interpret results in context

Electrolyte results are most useful when interpreted alongside symptoms, the rate of change, kidney function, medicines, and ECG findings. Adult ranges are approximate: use the laboratory’s reference range and the patient’s baseline. A dangerous symptom or ECG change warrants urgent action even when the laboratory result is only moderately abnormal.

Approximate adult ranges:

• Sodium $(\mathrm{Na}^+)$: $135\text{–}145\,\mathrm{mEq/L}$

• Potassium $(\mathrm{K}^+)$: $3.5\text{–}5.0\,\mathrm{mEq/L}$

• Total calcium $(\mathrm{Ca}^{2+})$: $8.8\text{–}10.4\,\mathrm{mg/dL}$

• Magnesium $(\mathrm{Mg}^{2+})$: $1.8\text{–}2.6\,\mathrm{mg/dL}$

• Phosphate $(\mathrm{PO}_4^{3-})$: $2.5\text{–}4.5\,\mathrm{mg/dL}$

Prioritize assessment and escalation

Begin with the patient rather than the laboratory value. Assess airway, breathing, circulation, vital signs, mental status, muscle strength, reflexes, and relevant symptoms.

Time-critical findings include seizure, new confusion, fainting, marked weakness or paralysis, tetany, respiratory difficulty, hypotension, palpitations, or an abnormal ECG. These findings require prompt escalation; initiate the emergency response according to facility protocol when indicated.

Review trends, kidney function, urine output, fluid balance, recent losses or infusions, and relevant medicines or supplements. If a result is unexpected, consider specimen error, such as hemolysis causing a falsely high potassium result, and follow instructions for repeat testing. Do not let repeat testing delay urgent assessment or escalation.

Use ordered monitoring and treatment. Obtain or review an ECG when potassium or other cardiac-risk abnormalities are significant, report critical findings promptly, and reassess after treatment. Do not independently give or withhold replacement or change fluids. Never administer potassium by IV push.

Sodium and neurologic risk

Hyponatremia

Hyponatremia is a sodium concentration below $135\,\mathrm{mEq/L}$. It may result from excess water relative to sodium, including some medication effects, or from sodium and fluid losses. Findings may progress from nausea, headache, and lethargy to confusion, seizures, or coma, especially when the decrease is acute or severe.

Check neurologic status and fluid balance. Promptly report new or worsening neurologic symptoms and use seizure precautions when indicated. Severe symptomatic cases require urgent clinician-directed treatment. Sodium must be corrected carefully because overly rapid correction can cause serious neurologic injury.

Hypernatremia

Hypernatremia is a sodium concentration above $145\,\mathrm{mEq/L}$ and usually reflects too little body water relative to sodium. Thirst, agitation, confusion, muscle twitching, seizures, or coma can occur.

Assess access to water, intake and output, and signs of volume depletion or overload. Promptly escalate altered mental status or seizures. Fluid replacement must be prescribed and monitored because the plan depends on volume status and the duration of the abnormality; correction that is too rapid can cause harm.

Potassium and cardiac risk

Hypokalemia

Hypokalemia is a potassium concentration below the reference range and commonly follows gastrointestinal losses or potassium-wasting medicines. Weakness, cramps, reduced bowel motility, and dysrhythmias may occur. ECG changes can include flattened T waves and prominent U waves.

A low result is especially concerning when accompanied by ECG changes, severe weakness, cardiac disease, or digoxin use. Report significant abnormalities, monitor rhythm when indicated, and give replacement only as ordered and at the prescribed rate.

Hyperkalemia

Hyperkalemia is a potassium concentration above the reference range. It is often associated with impaired kidney excretion, certain medicines, or cell injury. It may cause weakness or paralysis, but can be asymptomatic until dangerous conduction changes or dysrhythmias appear.

Obtain or review an ECG and promptly escalate a markedly elevated result, symptoms, or ECG changes. Hemolysis can falsely elevate a sample, so repeat testing may be needed when the result is unexpected. Do not assume the result is false or delay urgent care if the patient is unstable.

Calcium and neuromuscular changes

Hypocalcemia

Hypocalcemia is a total calcium concentration below about $8.8\,\mathrm{mg/dL}$. It can cause tingling around the mouth or in the fingers, cramps, muscle spasms, and tetany. Severe cases can cause seizures, laryngospasm, or cardiac effects, including a prolonged QT interval.

Check symptoms and ECG when indicated. Promptly escalate tetany, seizure, breathing difficulty, or significant rhythm changes. Interpret total calcium with albumin, and consider ionized calcium when protein levels are abnormal or symptoms do not match the total result.

Hypercalcemia

Hypercalcemia is a total calcium concentration above about $10.4\,\mathrm{mg/dL}$. It may cause constipation, nausea, thirst, frequent urination, weakness, and confusion. More severe elevation can impair consciousness, kidney function, and cardiac rhythm.

Assess mental status, hydration, and urine output. Promptly report confusion, significant weakness, or a markedly elevated result. Fluids and other treatment depend on the patient’s condition and must be clinician-directed.

Magnesium, reflexes, and breathing

Hypomagnesemia

Hypomagnesemia is a magnesium concentration below about $1.8\,\mathrm{mg/dL}$. It may occur with poor intake, gastrointestinal losses, alcohol use, or some diuretics. Tremor, cramps, hyperreflexia, tetany, seizures, and dysrhythmias can occur.

Low magnesium may coexist with hypokalemia or hypocalcemia and make them harder to correct. Report neuromuscular symptoms or rhythm changes, monitor related electrolytes, and administer replacement only as ordered.

Hypermagnesemia

Hypermagnesemia is a magnesium concentration above about $2.6\,\mathrm{mg/dL}$, particularly concerning with impaired kidney function or use of magnesium-containing medicines. Watch for diminished reflexes, hypotension, lethargy, slow or difficult breathing, and ECG changes. New respiratory depression, hypotension, or reduced level of consciousness requires immediate escalation and supportive care according to protocol.

Phosphate, calcium, and muscle function

Hypophosphatemia

Hypophosphatemia is a phosphate concentration below $2.5\,\mathrm{mg/dL}$. It may follow malnutrition, alcohol use, or refeeding. Severe deficiency can cause profound weakness, respiratory muscle failure, heart failure, confusion, seizures, or coma. Escalate respiratory or neurologic changes promptly; replacement requires monitoring and an order.

Hyperphosphatemia

Hyperphosphatemia is a phosphate concentration above $4.5\,\mathrm{mg/dL}$. It often accompanies kidney dysfunction and may lower calcium. The phosphate result may have few direct symptoms, so assess for associated hypocalcemia, including tingling, cramps, tetany, or seizures, and review kidney function. Report symptomatic hypocalcemia or a marked abnormality; treatment depends on the cause and is clinician-directed.

Connect patterns to clinical priorities

Match the assessment to the electrolyte pattern: prioritize neurologic changes with sodium abnormalities; ECG or muscle changes with potassium abnormalities; tetany or confusion with calcium abnormalities; reflexes and respiratory status with magnesium abnormalities; and severe weakness or respiratory impairment with low phosphate.

Rapid changes, symptoms, ECG findings, kidney impairment, and the overall clinical picture can make a result urgent. Escalate concerning findings promptly and follow ordered monitoring and treatment rather than treating a laboratory value in isolation.