Sodium, potassium, calcium, phosphorus, magnesium, bicarbonate. The kidney regulates all of them, minute to minute, and when it falters the numbers move.
Most electrolyte abnormalities are found on a routine blood test in someone who feels fine. Some are emergencies. Telling those apart is the work.
The thing worth understanding
An abnormal electrolyte is a symptom, not a diagnosis.
Low sodium is almost never a sodium problem — it is a water problem, and treating it with salt misunderstands the physiology. High potassium is often blamed on a kidney-protective medication that should not be stopped. A low bicarbonate that looks trivial on paper accelerates bone and muscle loss.
Each of these gets managed wrong in predictable ways, and the corrections have consequences. Sodium raised too quickly causes permanent neurologic injury. Potassium treated by abandoning an ACE inhibitor costs the patient the drug protecting their kidney.
The number tells you something is wrong. It does not tell you what, and it does not tell you what to do.
| Electrolyte | Too low | Too high |
|---|---|---|
| Sodium | Confusion, falls | Thirst, agitation |
| Potassium | Weakness, cramps | Dangerous heart rhythms |
| Calcium | Tingling, spasms | Fatigue, kidney stones |
Signs of an electrolyte imbalance
Most people with an electrolyte imbalance have no symptoms. The abnormal value shows up on routine bloodwork. When symptoms do appear, they depend on which electrolyte is off and how fast it moved.
The four warning signs I take most seriously:
- Muscle weakness or cramps, especially in someone with kidney disease or a new water pill.
- Palpitations or an irregular heartbeat. Potassium is the usual cause, and it can be dangerous.
- New confusion, unsteadiness, or falls in an older adult. Low sodium is often behind this.
- Tingling around the mouth or in the fingers, or muscle spasms. This points to low calcium or low magnesium.
Fatigue, nausea, and headache happen too, but they are vague and have many other explanations.
Older adults are the group most often missed. Low sodium in someone over 70 can look like ordinary slowing down: a little more forgetful, a little less steady on their feet. It is treatable. The falls it causes are not.
What causes an electrolyte imbalance
The usual causes are ordinary ones:
- Fluid loss from vomiting, diarrhea, heavy sweating, or not drinking enough.
- Medications. Diuretics (water pills), ACE inhibitors and ARBs, NSAIDs like ibuprofen, some antidepressants, and long-term acid reducers (proton pump inhibitors) are the most common.
- Kidney disease, which limits how well the kidney decides what to keep and what to let go.
- Heart failure and cirrhosis, which change how the body handles salt and water.
- Hormone problems involving the thyroid or adrenal glands, or SIADH.
- Heavy alcohol use and poor food intake.
In practice, a medication is the cause more often than anything else. The first thing I do with an abnormal result is read the medication list.
Is it dehydration?
Dehydration is the most common reason electrolytes run low after a stomach bug or a long day outside in Houston heat. It usually corrects with fluids and normal meals once the illness passes.
If the value is still off on a repeat test after you are well and eating and drinking normally, dehydration is not the explanation. That is when it needs a closer look.
One caution: most salt substitutes are potassium chloride. People with kidney disease, or anyone on an ACE inhibitor, ARB, or spironolactone, should not use them without asking first.
How an electrolyte imbalance is treated
The cause gets fixed first. The number follows.
- Stop or adjust the medication responsible, if there is one.
- Replace what is low, by mouth when it is mild and by IV when it is severe.
- For high potassium, adjust the diet or a diuretic, or add a potassium binder, so kidney-protective drugs can stay on.
- Correct sodium slowly, by no more than about 8 to 10 points in the first 24 hours.
- Recheck labs on a schedule, so the correction is measured and not guessed.
Mild, stable imbalances are managed in clinic. A potassium above 6.5, a sodium below 120, or any imbalance causing confusion, a seizure, or an irregular heartbeat is treated in the hospital.
Where to go from here
Hyponatremia — low sodium. Why it is a water problem, why the correction rate matters more than the target, and what osmotic demyelination is.
Hyperkalemia — high potassium. When it is an emergency, and why stopping the ACE inhibitor is usually the wrong trade.
Metabolic Acidosis — low bicarbonate. The abnormality that looks minor and is not.
CKD Mineral & Bone Disorder — calcium, phosphorus, and parathyroid hormone in kidney disease.
Why a nephrologist
The kidney is the organ that sets these values. An electrolyte abnormality in someone with kidney disease is rarely isolated, and it is rarely random — it points at a mechanism, and the mechanism determines the treatment.
If a lab result was flagged and nobody explained why it happened, that is the question worth answering.