Also known as: Blood chloride
Name: Chloride, Cl
Related tests: Electrolytes, Potassium, Sodium
Why is the test done?
To assess the patient’s fluid, salt and acid-base balance
and to monitor any treatment.
When is the test done?
The test is done routinely together with other electrolytes; it may also be done when the doctor suspects an acid-base or fluid and salt imbalance.
What samples are required?
A blood sample from a vein or a urine sample.
What is being analysed?
Chloride is a negatively charged electrolyte that, together with other electrolytes such as potassium, sodium and bicarbonate, helps maintain the body’s fluid, salt and acid-base balance. Chloride is present in all body fluids but at the highest concentration in the extracellular fluids, with which the plasma is in balance. To keep body fluids electrically neutral, the plasma chloride concentration follows that of sodium; however, plasma chloride can change independently of sodium when the acid-base balance is disturbed. Chloride, taken in through food and table salt (sodium chloride), is absorbed in the gut, and any excess is eliminated in the urine. The plasma chloride level is normally kept within a narrow range, with slight falls after meals, when chloride is used to produce hydrochloric acid in the stomach
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Plasma chloride is often requested together with other electrolytes as part of a regular medical check-up. Electrolytes are also requested to check for, and assess the severity of, a fluid and salt or acid-base imbalance; in the latter case the electrolyte panel should be combined with blood gas analysis. As well as at diagnosis, electrolytes are requested during treatment to monitor its effects.
Urine chloride can also be used to study acid-base balance: for example, in people with alkalosis, urine chloride usually falls after large losses of salts, as with dehydration or repeated vomiting; conversely, urine chloride rises in alkalosis caused by an excess of hormones such as cortisol and aldosterone. In patients on a low-sodium diet, measuring urine sodium and chloride can be useful to check whether the patient is keeping to the diet.
When is it requested?
Plasma chloride is almost never requested on its own, but together with other electrolytes; these panels are often requested as part of a routine medical check-up or to monitor a patient with acute or chronic illness. These tests may be requested periodically when the patient has conditions that disturb fluid and salt balance or takes medicines with similar effects. For example, an electrolyte panel is commonly requested for high blood pressure, heart failure, and liver or kidney disease.
Like plasma chloride, urine chloride can be measured on its own or, more often, together with other electrolytes such as sodium.
What does the test result mean?
The blood chloride value must always be assessed together with blood sodium: since chloride is the main ion accompanying sodium, proportional changes in plasma sodium and chloride reflect disorders of hydration. Blood chloride can also change when acid-base balance is disturbed: hyperchloraemia, for example, can occur with metabolic acidosis or with respiratory alkalosis caused by hyperventilation.
Hypochloraemia can occur after repeated vomiting, chronic diarrhoea or any chronic lung disease, such as emphysema, that can cause respiratory acidosis, but also in response to excessive loss of acids and resulting metabolic alkalosis.
Is there anything else I should know?
Medicines that change blood sodium also cause parallel changes in plasma chloride. In addition, taking large amounts of sodium bicarbonate or antacids can lower blood chloride.