In short
- Normal potassium is 3.5–5.1 mmol/L and normal sodium is 135–145 mmol/L. For both, mmol/L equals mEq/L, the US unit.
- A mildly high potassium is often a sampling artefact: a haemolysed sample, a long tourniquet or fist clenching. A careful repeat draw usually settles it.
- True high potassium is most often linked to weaker kidneys and medicines such as ACE inhibitors, potassium-sparing diuretics and NSAIDs.
- Low potassium usually comes from losses: vomiting, diarrhoea, laxatives or diuretics. Low magnesium makes it harder to correct.
- Sodium mostly reflects water balance, not how much salt you eat.
- Potassium of 6.5 mmol/L or more, or below 3.0 mmol/L, needs same-day medical contact.
Potassium and sodium are the two electrolytes people most often find flagged on a routine report. Both are kept in a narrow range, and both can be off for reasons that have nothing to do with disease. This guide shows the ranges, the sampling trap behind many high potassium results, and the medicines and patterns that matter.
What is the normal range for potassium and sodium?
Normal potassium is 3.5 to 5.1 mmol/L and normal sodium is 135 to 145 mmol/L. In US reports the unit is mEq/L, and the numbers are the same. Potassium is the main electrolyte inside cells, and sodium the main one outside them. Both matter for the heart, muscles and nerves.
| Marker and value (mmol/L = mEq/L) | How Blood Lab 360 reads it |
|---|---|
| Potassium below 3.0 | Markedly low. Can disturb heart rhythm; same-day contact with a doctor. |
| Potassium 3.0–3.4 | Low. Common causes are vomiting, diarrhoea, diuretics and laxatives. |
| Potassium 3.5–5.1 | Within the reference range. |
| Potassium above 5.1 to 5.9 | Mildly raised. Often a sampling effect; a repeat draw makes sense. |
| Potassium 6.0–6.4 | Moderately raised. Same-day assessment with kidney function and a medicine review. |
| Potassium 6.5 and above | Severely raised. Potentially life-threatening; urgent hospital assessment. |
| Sodium below 135 | Low sodium. Seek advice. |
| Sodium 135–145 | Within the reference range. |
| Sodium above 145 | High sodium. Seek advice. |
| Chloride 98–107 | Within the reference range. |
Source: potassium bands follow the UK Kidney Association guideline on hyperkalaemia in adults (2023); sodium bands follow the ESE, ERA-EDTA and ESICM hyponatraemia guideline (2014). Chloride uses a common laboratory reference interval. Reference ranges differ slightly between laboratories.
StatPearls grades low potassium the same way: mild at 3.0–3.4, moderate at 2.5–3.0 and severe below 2.5 mmol/L.
Why is my potassium high? Check the sample first
The most common reason for a mildly high potassium on a routine report is the blood sample, not your body. StatPearls explains that false high potassium, called pseudohyperkalaemia, often comes from haemolysis. Red cells break during collection and release their potassium into the sample.
Two habits at the draw make this more likely. A tourniquet left on for a long time is one. Clenching and relaxing your fist again and again is the other. MedlinePlus warns that repeated fist clenching just before or during the test can temporarily raise potassium and give an incorrect result. StatPearls adds that very high white cell or platelet counts can also cause a false high value.
Clues that point to an artefact:
- The lab adds a comment such as "haemolysed" or "haemolysis".
- Potassium is only mildly high, while eGFR and creatinine are normal.
- You take no medicine that raises potassium, and you feel well.
- A repeat draw with a relaxed hand is normal.
At the repeat draw, keep your hand relaxed and do not pump your fist. Tell the phlebotomist the last result was high. The blood test preparation guide explains why sitting quietly for a few minutes helps too.
What causes true high potassium?
True high potassium, called hyperkalaemia, is most often linked to reduced kidney function and to medicines that make the kidneys hold on to potassium. StatPearls notes that kidney disease on its own usually does not cause it until filtration falls below about 30 mL/min. Below that level, or with extra triggers, it becomes common.
StatPearls lists these medicine groups as contributors:
- Blood pressure and heart medicines that block the renin-angiotensin system, such as ACE inhibitors and angiotensin receptor blockers.
- Potassium-sparing diuretics.
- Non-steroidal anti-inflammatory painkillers (NSAIDs).
- Digoxin.
MedlinePlus adds Addison disease, injuries, burns or surgery, and poorly controlled type 1 diabetes. The risk rises when causes stack up: a lower eGFR, an ACE inhibitor and regular painkillers together. Never stop a prescribed medicine on your own because of one result. Your doctor weighs the benefit of the medicine against the potassium level.
Why is my potassium low?
Low potassium, called hypokalaemia, usually means the body is losing potassium through the gut, the kidneys or the skin. StatPearls lists diarrhoea, vomiting, laxative overuse, loop diuretics, heavy sweating, insulin and inhaled asthma relievers of the beta-agonist type. MedlinePlus adds prescription diuretics in general, alcohol use disorder and some adrenal disorders.
Symptoms include muscle weakness, cramps, tiredness, palpitations and constipation. StatPearls notes that marked muscle weakness appears below 2.5 mmol/L. The heart rhythm risk is highest in older people, people with heart disease and people taking digoxin.
Magnesium matters here. StatPearls explains that low magnesium often occurs with low potassium and increases potassium loss in the urine. Potassium replacement then works poorly until magnesium is corrected. Our magnesium article explains how to read that marker.
What does low sodium mean?
Low sodium, below 135 mmol/L, usually means there is too much water relative to sodium, not that you eat too little salt. The body controls sodium through thirst, the kidneys and the hormone ADH. That is why sodium on a report is mainly a signal about water balance.
MedlinePlus lists two main routes. One is sodium loss through diarrhoea or vomiting. The other is conditions that make the body hold extra fluid, which dilutes sodium: kidney disease, liver cirrhosis, heart failure, and some brain and lung diseases. Some medicines lower sodium too, including many over-the-counter painkillers and some antidepressants. Addison disease and malnutrition are rarer causes.
Symptoms of low sodium include weakness, tiredness, confusion, muscle twitching and seizures. A rapid fall is dangerous for the brain. Do not try to fix sodium by adding salt or drinking less on your own.
High sodium, above 145 mmol/L, almost always means too little water. MedlinePlus names dehydration from drinking too little, diarrhoea or diuretics, plus rarer adrenal, kidney and hormone causes. Thirst, passing little urine and confusion are the typical signs.
Patterns: electrolytes with kidney markers
Electrolytes make sense only next to the kidney markers from the same report. These are the combinations Blood Lab 360 looks at:
- Potassium mildly high, eGFR and creatinine normal. A sampling artefact is likely, especially with a haemolysis note. Repeat the draw.
- Potassium high and eGFR below 60. True hyperkalaemia is more likely. KDIGO (2024) uses eGFR below 60 as the threshold for reduced kidney function. A medicine review is the next step. See eGFR and creatinine.
- Potassium low and magnesium low. Both need correcting together, or potassium will not come up.
- Potassium low while taking a diuretic. A common medicine effect. Tell your doctor; do not start potassium supplements yourself.
- Sodium high, urea high, creatinine high. This pattern fits dehydration. Our urea and BUN article explains how urea helps tell dehydration from kidney disease.
- Sodium low while taking an antidepressant or regular painkillers. A possible medicine effect worth raising with your doctor.
One value just outside the range is rarely an emergency. The trend across repeat tests, and the pattern with eGFR, tell you much more.
Same-day medical contact if potassium is 6.5 mmol/L or higher (urgent hospital assessment) or below 3.0 mmol/L. Potassium of 6.0–6.4 mmol/L also needs a doctor's assessment the same day. Go to emergency care straight away if any abnormal potassium comes with palpitations, an irregular heartbeat or marked muscle weakness. The same applies if abnormal sodium comes with confusion, severe headache, vomiting, drowsiness or seizures.
How Blood Lab 360 reads this
Blood Lab 360 reads potassium in six bands based on the UK Kidney Association guideline. It reads sodium in three bands from the European hyponatraemia guideline. It checks eGFR, creatinine, chloride and magnesium from the same report. When potassium is mildly high and kidney function is normal, it explains the sampling effect and suggests a repeat draw.
The app only knows about your medicines if you note them, so add diuretics, blood pressure tablets and painkillers. For a stable value, it suggests a potassium re-test in about 12 weeks and a sodium re-test in about 24 weeks. A clearly abnormal potassium should be repeated much sooner, as your doctor advises. The app does not tell you to change potassium with supplements or diet without a doctor. For values just outside the range, see what an out-of-range result means.
Frequently asked questions
What is the normal range for potassium?
3.5 to 5.1 mmol/L, which is the same as 3.5 to 5.1 mEq/L. Labs differ slightly. Values from 5.1 to 5.9 are mildly raised and are often repeated first.
Can a blood draw make potassium falsely high?
Yes, and it is common. Haemolysis during collection, a tourniquet left on too long or repeated fist clenching can release potassium into the sample. A careful repeat draw with a relaxed hand usually shows the true value.
Why is my potassium low?
Most often because of losses: vomiting, diarrhoea, laxatives, heavy sweating or diuretics. Low magnesium can keep it low. A value below 3.0 mmol/L needs same-day medical contact.
Do blood pressure medicines affect potassium?
Yes. ACE inhibitors, angiotensin receptor blockers and potassium-sparing diuretics can raise potassium. Many other diuretics lower it. Do not stop them yourself; ask your doctor to review the result.
What is a normal sodium level, and what does low sodium mean?
Normal sodium is 135 to 145 mmol/L. Below 135 usually means too much water relative to sodium, from fluid retention, losses or some medicines. With confusion or seizures, it is an emergency.
Should I eat less potassium if my result is high?
Not on your own. First repeat the test to rule out a sampling effect. If it is confirmed, especially with weaker kidneys, your doctor decides whether diet or medicines need to change.
Upload it and get every value explained for your age and sex, with a source for every range. Free for your first report.
Upload your report — free →Sources
- MedlinePlus (NIH): Potassium Blood Test (2024)
- MedlinePlus (NIH): Sodium Blood Test (2024)
- StatPearls (NCBI Bookshelf): Hypokalemia (2023)
- KDIGO: 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (2024)
- StatPearls (NCBI Bookshelf): Hyperkalemia (2025)
Links checked on 14 Sep 2026. The marker ranges above carry their own source next to each row.
Related
Blood chemistry panel normal values for ALT, AST, GGT, CK, creatinine and glucose, each with a source, plus what S- means on a lab report and µkat/L to U/L.
What do eGFR and creatinine mean? How kidney function is assessed, when a value is worrying and how to protect your kidneys naturally.
High homocysteine often means low B12, folate or B6, or weaker kidneys. See the normal range, causes, what to test next and what lowering it can't do.
This article is for information only and is not a substitute for medical advice. Talk to your doctor about your results.