Electrolytes — Sodium, Potassium and Calcium
Electrolytes are minerals that carry an electrical charge when dissolved in blood and other body fluids. They help regulate fluid balance, nerve signals, muscle contractions, and heart rhythm.
Three particularly important electrolytes measured in routine blood tests are sodium, potassium, and calcium.
Abnormal electrolyte levels become more common with age because kidney function, medications, hydration, and certain medical conditions can affect how the body regulates these minerals.
An important distinction is that the amount of a mineral in the blood does not always reflect how much of it is stored in the body.
Sodium — Regulating Fluid Balance
Sodium helps regulate the movement of water between cells and the bloodstream. It also supports nerve and muscle function.
A typical blood sodium reference range is 135–145 mmol/L.
Low Sodium — Hyponatremia
Hyponatremia occurs when blood sodium falls below the normal range.
It is often caused by an excess of water relative to sodium rather than simply eating too little salt.
Possible causes include:
Certain diuretics and antidepressants
Heart, kidney, or liver disease
Hormonal disorders
Excessive water intake
Vomiting or diarrhea
Inappropriate release of antidiuretic hormone (SIADH)
Symptoms can include nausea, headache, weakness, confusion, and balance problems.
In older adults, even mild chronic hyponatremia has been associated with increased falls and fractures.
Severe or rapidly developing hyponatremia can cause seizures and is a medical emergency.
High Sodium — Hypernatremia
Hypernatremia occurs when blood sodium rises above the normal range.
It most often reflects insufficient water relative to sodium, frequently because of dehydration.
Older adults may be especially vulnerable because thirst perception can decline with age.
Possible causes include:
Inadequate fluid intake
Fever or heavy sweating
Diarrhea
Certain kidney disorders
Impaired access to drinking water
Treatment depends on the cause and severity. Significant sodium abnormalities must be corrected carefully because overly rapid correction can cause neurological injury.
Potassium — Essential for Heart and Muscle Function
Potassium helps regulate electrical activity in nerves and muscles, particularly the heart.
A typical blood potassium reference range is approximately 3.5–5.0 mmol/L.
Even relatively small changes can sometimes affect heart rhythm.
Low Potassium — Hypokalemia
Low potassium can result from:
Diuretic medications
Vomiting or diarrhea
Certain hormonal disorders
Inadequate intake, particularly when combined with other causes
Symptoms may include muscle weakness, cramps, fatigue, and irregular heartbeats.
Severe hypokalemia can cause dangerous cardiac arrhythmias.
High Potassium — Hyperkalemia
High potassium is particularly important in people with reduced kidney function.
Possible causes include:
Chronic kidney disease
Certain blood pressure medications, including ACE inhibitors and ARBs
Potassium-sparing diuretics
Potassium supplements or salt substitutes
Certain hormonal disorders
A falsely elevated result can also occur when red blood cells break during blood collection.
Significantly elevated potassium can cause dangerous heart rhythm disturbances, sometimes without noticeable symptoms.
This is why an unexpectedly high potassium result may require prompt confirmation and medical evaluation.
Calcium — More Than Bone Health
Calcium is best known for maintaining strong bones and teeth, but it also supports muscle contraction, nerve signaling, and blood clotting.
A typical total blood calcium reference range is approximately 8.5–10.5 mg/dL.
However, total calcium is influenced by albumin, a protein in the blood.
When albumin is abnormal or the calcium result is unclear, a doctor may order an ionized calcium test, which measures the biologically active form.
Low Calcium — Hypocalcemia
Low calcium may be associated with:
Kidney disease
Parathyroid gland disorders
Magnesium deficiency
Certain medications
Symptoms can include tingling around the mouth or in the fingers, muscle cramps, and, in severe cases, spasms or abnormal heart rhythms.
High Calcium — Hypercalcemia
High blood calcium may result from:
Overactive parathyroid glands
Certain cancers
Excessive vitamin D or calcium intake in some circumstances
Certain medications
Other less common conditions
Symptoms can include constipation, increased urination, thirst, fatigue, and confusion.
Persistently elevated calcium deserves evaluation, even when symptoms are mild.
Primary hyperparathyroidism, a condition involving excessive parathyroid hormone production, becomes more common with age and is an important cause of elevated calcium.
What About Magnesium?
Magnesium is another essential electrolyte involved in hundreds of biochemical reactions.
It supports muscle and nerve function, blood pressure regulation, and normal heart rhythm.
A typical serum magnesium reference range is approximately 1.7–2.2 mg/dL, depending on the laboratory.
Low magnesium can occur with gastrointestinal losses, certain medications, alcohol use, and some kidney-related conditions.
It can also contribute to low potassium or low calcium.
One limitation is that serum magnesium does not always accurately reflect the body's total magnesium stores, because most magnesium is located inside cells and bones.
Magnesium is not always included in a routine metabolic panel and may need to be ordered separately.
What About Chloride and Bicarbonate?
Two additional measurements commonly included in routine metabolic panels are chloride and bicarbonate.
Chloride helps regulate fluid balance and acid-base balance.
Bicarbonate, usually reported as CO2 on a metabolic panel, helps indicate whether the body is maintaining an appropriate acid-base balance.
Abnormal results can occur with kidney disease, respiratory disorders, dehydration, diarrhea, and other conditions.
These measurements are generally interpreted together rather than individually.
How Do Medications Affect Electrolytes?
Medication effects are particularly important for older adults.
Examples include:
Diuretics: May lower sodium, potassium, or magnesium, although potassium-sparing diuretics can increase potassium.
ACE inhibitors and ARBs: Can raise potassium.
Certain antidepressants: Can contribute to low sodium.
Calcium or vitamin D supplements: Excessive intake can sometimes contribute to high calcium.
Laxatives: Excessive use or diarrhea can cause fluid and electrolyte losses.
People taking these medications may need periodic electrolyte testing, particularly when kidney function changes.
What Is the Difference Between a Basic and Comprehensive Metabolic Panel?
Two commonly ordered blood panels include several electrolyte measurements.
Basic Metabolic Panel (BMP)
Typically includes:
Sodium
Potassium
Chloride
Bicarbonate (CO2)
Calcium
Glucose
Blood urea nitrogen (BUN)
Creatinine
Comprehensive Metabolic Panel (CMP)
Includes the BMP measurements plus additional tests, such as albumin, total protein, bilirubin, and several liver enzymes.
These panels provide a broad picture of kidney function, electrolyte balance, glucose metabolism, and, in the CMP, liver-related measurements.
Why Electrolyte Balance Matters More With Age
Several age-related changes can make electrolyte disturbances more likely:
Reduced kidney reserve
Changes in thirst perception
Greater use of prescription medications
Increased vulnerability to dehydration during illness
Chronic conditions affecting fluid balance
For older adults, electrolyte abnormalities may sometimes present as weakness, confusion, dizziness, or falls rather than obvious symptoms related to a particular mineral.
Sudden confusion, seizures, severe weakness, or an irregular heartbeat warrants urgent medical attention.
The Bottom Line
Sodium, potassium, and calcium are essential for maintaining fluid balance, nerve activity, muscle function, and heart rhythm.
Abnormal results may reflect dehydration, kidney disease, hormonal problems, medications, or other underlying conditions.
Magnesium, chloride, and bicarbonate provide additional information about mineral balance and metabolism.
For older adults, the most useful approach is to interpret electrolyte results together with kidney function, medications, symptoms, and changes over time.
An abnormal electrolyte level should not automatically lead to taking more or less of a mineral without understanding the cause.
Learn More
Explains what electrolytes do, why doctors test them, and what abnormal results may indicate.
Describes the eight measurements commonly included in a basic metabolic panel, including sodium, potassium, calcium, glucose, & kidney function tests.
Explains why potassium is particularly important for people with reduced kidney function and how medications can affect blood potassium levels.