Medically reviewed by Dr. Farhana Mukhtar, M.B.B.S., M.Phil (Pb.), Consultant Chemical Pathologist, Al-Nasar Lab & Diagnostic Centre. Updated November 2026.
Quick answer: A serum electrolytes test measures sodium, potassium and chloride, often with bicarbonate. These salts control fluid balance, nerve signals, muscle contraction and heart rhythm. Typical adult ranges are roughly sodium 135 to 145 mmol/L and potassium 3.5 to 5.0 mmol/L. No fasting is needed. Diarrhoea, vomiting, heat, kidney problems and several common blood pressure tablets are the usual reasons they go out of range.
Book an electrolytes test: call 0300 0341944, or arrange home sample collection across Lahore on 0309 1166944.
What each electrolyte does
| Electrolyte | Main role | Typical adult range |
|---|---|---|
| Sodium | Water balance, especially in the brain | about 135 to 145 mmol/L |
| Potassium | Muscle and heart rhythm | about 3.5 to 5.0 mmol/L |
| Chloride | Fluid balance, moves with sodium | about 98 to 107 mmol/L |
| Bicarbonate | Acid and base balance | about 22 to 29 mmol/L |
Ranges vary slightly between laboratories, so read the range on your own report.
When is the test ordered?
- Diarrhoea or vomiting lasting more than a day or two, particularly in children and older adults
- Weakness, confusion, muscle cramps or palpitations
- Anyone taking diuretics, ACE inhibitors or similar blood pressure tablets
- Kidney disease, where potassium in particular needs regular monitoring
- Uncontrolled diabetes
- Before surgery, and routinely in hospital
- Heat exhaustion
Low sodium
Low sodium, called hyponatraemia, is the most common electrolyte problem in older adults. The brain is sensitive to it, so symptoms are often confusion, unsteadiness and falls rather than anything that obviously points to a salt problem.
Common causes include diuretics, especially the thiazide type, some antidepressants, vomiting and diarrhoea, heart failure, liver disease, and drinking very large amounts of plain water. A slowly developing low sodium may cause few symptoms. A rapid fall is dangerous.
Low sodium must be corrected slowly and under medical supervision. Correcting it too fast can cause serious brain injury, so this is never something to fix at home with salt.
High and low potassium
Potassium has the narrowest safe range of the group, because both high and low levels affect heart rhythm.
Low potassium causes weakness, cramps and palpitations. It often follows diarrhoea, vomiting or diuretic tablets.
High potassium often causes no symptoms at all until it disturbs the heart rhythm, which is why it is taken seriously even when the patient feels well. Kidney disease and some blood pressure medicines are common causes, especially in combination.
Why a high potassium result is sometimes not real
This is worth knowing, because a falsely high potassium is common and causes needless worry.
Red blood cells contain a great deal of potassium. If cells break during collection or before the sample is processed, potassium leaks into the serum and the result reads high. This is called haemolysis, and the laboratory will usually flag it on the report.
It is made more likely by a tight tourniquet left on for a long time, repeated fist clenching, a difficult draw, or a delay before the sample reaches the laboratory. When a high potassium does not fit the clinical picture, the usual step is a prompt, carefully collected repeat.
Heat, diarrhoea and oral rehydration
Lahore summers and the high rates of gastroenteritis in Pakistan make electrolyte loss common. For most adults and children with diarrhoea, oral rehydration solution replaces both water and salts in the right proportions. Plain water alone does not, and very sugary drinks can make diarrhoea worse.
Seek medical care for a child who is drowsy, passing little urine or unable to keep fluids down, and for any adult who becomes confused or very weak.
How to prepare
- No fasting is needed
- Take your usual medicines unless told otherwise, and bring a list of them
- Relax your hand during the draw. Repeated fist clenching can raise potassium
- Mention recent vomiting, diarrhoea or intravenous fluids
Electrolyte testing at Al-Nasar Lab
Al-Nasar Lab & Diagnostic Centre has provided laboratory testing in Lahore since 1996 and holds ISO 15189:2022 accreditation from the Pakistan National Accreditation Council. Serum electrolytes, sodium, potassium and chloride are available, usually alongside a kidney function test, with home sample collection across Lahore and same day reports.
See our accreditations, find your nearest collection centre, see our full test list, or contact us to book.
Frequently Asked Questions
Do I need to fast for an electrolytes test?
No. You can eat and drink normally.
What is a normal sodium level?
Roughly 135 to 145 mmol/L in adults, though ranges vary slightly between laboratories.
What is a normal potassium level?
Roughly 3.5 to 5.0 mmol/L. Both high and low levels can affect heart rhythm.
Why was my potassium high but my doctor is not worried?
Potassium can read falsely high if red cells break during or after collection. A careful repeat usually settles the question.
Can blood pressure tablets affect electrolytes?
Yes. Diuretics often lower sodium and potassium, while some other blood pressure medicines can raise potassium. Regular testing is common for people on these medicines.
This article is for general information and is not a substitute for medical advice. Please discuss your results with a qualified doctor.
