128 Chloride (Cl)

Chloride: normal about 98–107 mmol/L; role in acid–base balance, anion gap, causes of high and low chloride.

Chloride (Cl⁻) is the main negatively charged ion outside cells. Together with sodium it determines the osmolality of body fluids, and it plays a central role in acid–base balance: chloride and bicarbonate move in opposite directions to keep the blood electrically neutral. Chloride rarely changes on its own. Abnormal values usually point to a disturbance of water balance or of acid–base balance, which is why chloride is interpreted together with sodium and bicarbonate.

ElectrolytesAcid–base balanceAnion gap

Normal serum level98–107 mmol/L (some labs 96–106)

Hypochloraemia< 98 mmol/L

Hyperchloraemia> 107 mmol/L

Anion gapNa − (Cl + HCO₃) ≈ 8–12

Figure 1. Chloride zones and the acid–base disorders that typically accompany them.

The anion gap

The anion gap is calculated as Na⁺ − (Cl⁻ + HCO₃⁻) and is normally about 8–12 mmol/L. The exact range depends on the laboratory method. In metabolic acidosis it helps separate two groups. In high-gap acidosis (ketoacidosis, lactic acidosis, kidney failure, poisoning with methanol, ethylene glycol or salicylates), extra acids are present and chloride is usually normal. In normal-gap (hyperchloraemic) acidosis (diarrhoea, renal tubular acidosis, large volumes of saline), bicarbonate is lost and chloride rises.

Low chloride — hypochloraemia

Vomiting or gastric drainage — loss of hydrochloric acid, causing metabolic alkalosis
Loop and thiazide diuretics
Chronic respiratory acidosis (COPD), where the kidneys retain bicarbonate and excrete chloride
Hyponatraemia from any cause; heart failure

High chloride — hyperchloraemia

Dehydration with water loss greater than salt loss (often with high sodium)
Diarrhoea and renal tubular acidosis (bicarbonate loss)
Large volumes of 0.9 % saline, which has more chloride than plasma
Respiratory alkalosis (hyperventilation), some medicines (acetazolamide)

In critically ill patients, hyperchloraemia caused by intravenous fluids has been associated with kidney injury and worse outcomes, which is why balanced crystalloid solutions are often preferred.

What to do

An isolated, slightly abnormal chloride is rarely important. Your doctor will interpret it together with sodium, potassium, bicarbonate (or blood gas), kidney function and your symptoms. Seek urgent care for persistent vomiting, severe diarrhoea, confusion or rapid deep breathing.

References

Berend K, van Hulsteijn LH, Gans ROB. Chloride: the queen of electrolytes? Eur J Intern Med. 2012;23(3):203–211. doi:10.1016/j.ejim.2011.11.013
MedlinePlus. Chloride — blood. U.S. National Library of Medicine. medlineplus.gov/ency/article/003485.htm

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 12 May 2024

Medical Book