Know Your Biomarkers: Serum Chloride

Chloride is the principal extracellular anion, existing in extracellular spaces in the form of sodium chloride or hydrochloric acid. It represents roughly 70% of the total negatively charged electrolytes or anions. Chloride is under the same influence as sodium and is affected by many of the same conditions that affect serum sodium levels, due to their reciprocal relationship. Aldosterone, which will cause increased reabsorption of sodium from the kidney, will also cause an increase in chloride reabsorption by the kidneys. Serum chloride levels will most often change in the same direction as serum sodium, i.e. if the serum sodium is decreased, we can expect to see a decreased serum chloride level as well.

Where does chloride come from?

Levels of chloride in the body are sustained by the intake of sodium chloride or salt. The average adult consumes between 6 to 12 grams of chloride/day. As mentioned earlier, serum levels of chloride are under the influence of the kidneys.

Functions of Chloride:

Chloride helps maintain cellular integrity by playing a role in influencing osmotic pressure and the movement of fluid and minerals through the cell membrane. It is also essential for a healthy acid-base balance. Chloride is also crucial for the synthesis of Hydrochloric acid or HCl in the parietal cells of the stomach.

Clinical Implications:

As we mentioned earlier, chloride plays a role in maintaining a healthy acid-base balance. Increased chloride levels are associated with metabolic acidosis. Chloride tends to have an inverse relationship to CO2 levels. In situations that cause a decreased CO2, like metabolic acidosis, you might expect to see an increase in chloride.

What about decreased chloride levels?

Well, we just discussed how important chloride is in the formation of HCl or stomach acid. When we see a low serum chloride we will want to look into low stomach acid, a condition called hypochlorhydria. Now, there are biomarkers to consider for hypochlorhydria, but a low chloride is one of the indicators of low stomach acid in your patients.

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