Since there is a formula that doesn’t require potassium, you may skip this step.
Note that all these electrolyte levels can be identified through a blood test. Pregnant women may notice different levels, too. We’ll discuss this in the next section.
First formula: Anion gap = Na⁺ + K⁺ – (Cl⁻ + HCO₃⁻). [6] X Trustworthy Source PubMed Central Journal archive from the U. S. National Institutes of Health Go to source This formula can be used if there is a value for potassium. However, the second equation is used more often than the first one. Second formula: Anion gap = Na⁺ – (Cl⁻ + HCO₃⁻). You can see that potassium is omitted in this second equation. This formula is more frequently used than the other, but you can use either of the two depending on your preferences.
Example 1: Na⁺ = 140, Cl⁻= 100, HCO₃⁻= 23AG= 140 – (98 + 23)AG = 24 The anion gap is 24. Therefore, the individual is positive for having a metabolic acidosis. Example 2: Na⁺ = 135, Cl⁻= 100, HCO₃⁻= 25AG= 135 – (100 + 25)AG = 10 The anion gap is 10. Therefore, the result is normal and the person does not have metabolic acidosis. It is within the normal range of 8 – 12 mEq/L. [8] X Trustworthy Source PubMed Central Journal archive from the U. S. National Institutes of Health Go to source
Determining the anion gap value is crucial in setting the arterial blood gas analysis or ABG. The basic concept is that net cation and anion charges must be equal to achieve balance in your body.
Anion gap reveals the presence of metabolic acidosis, where the pH levels in your body are off-kilter. It differentiates the causes of metabolic acidosis and helps confirm other findings. Ask your doctor to help wrap your brain around this process. Let’s take for instance that a patient has lactic acidosis (where there’s also a buildup of lactate. In this case, the serum bicarbonate levels will automatically reduce (because of the buildup) so that when you calculate for the anion gap, you’ll see that the anion gap increases.
A medical scientist or medical technologist extracts blood from a vein, likely in your arm. He or she may ask you if you have a history of latex allergies. If you do, they’ll use different materials to ensure you don’t have an allergic reaction. Inform them of any medical condition or medication that may cause excessive bleeding or if you have psychological issues associated with sharp items like needles. Your specimen will be kept inside a bio-refrigerator and kept in a queue for examination. When all is said and done, your doctor will contact you to discuss the findings.
Decreased anion gap can be correlated to various conditions such as hypo-albuminemia and bromide intoxication. A normal result is expected when a patient is recovering from diabetic ketoacidosis or recovering from bicarbonate loss due to prolonged diarrhea. An increase in anion gap may indicate lactic acidosis or renal failure. Interpretation of results may vary depending on various factors and underlying conditions experienced by the patient. A “normal” anion gap for pregnant women is slightly different. During the first trimester, normal anion gap ranges from 10 to 20 mmol/L. During the second and third trimester, normal value decreases from 10 to 11 to maximum of 18 mmol/L, respectively.
An increase in anion gap requires further testing – including testing for serum lactic acid, drug testing, testing your creatinine levels and serum ketones – to rule out possible causes of anion gap acidosis.
