How to Calculate Anion Gap and Identify Anion Gap Acidosis

The anion gap (AG) will be used as an indicator of the sort and severity of an acid-base imbalance. Your body maintains acid-base balance by retaining or releasing carbon dioxide (a relative acid) through your lungs or bicarbonate (a base) through your kidneys. Cations are positively charged molecules, and anions are negatively charged. The anion gap is the difference between the variety of cations and anions. The anion gap will be high, normal, or low (rare). A high anion gap indicates that there are more anions than cations, causing acidosis. In most causes of metabolic acidosis, the anion gap widens as bicarbonate (an anion base) is consumed to correct the acid-base imbalance (Kraut & Madias, 2007). A patient with metabolic acidosis who has a traditional anion gap has what is known as This style of acidosis is the results of renal, gastrointestinal, or exogenous lack of bicarbonate, which causes relative hyperchloremia.

How to calculate anion gap

The normal serum anion gap value is roughly 3 to 10 mEq/l (mean 6 mEq/l), but may vary between laboratories (Kraut & Madias, 2007). When calculating the anion gap CO₂ the patient’s basic metabolic panel (BMP) value is usually used as an equivalent value for HCO₃^– from arterial blood gas. This is suitable because the entire CO₂ content includes serum bicarbonate along with available types of carbon dioxide. Serum HCO₃^– accounts for about 95% of BMP’s total CO2 emissions₂Since BMP is less complicated to acquire than ABG generally, this measurement is often used to estimate serum HCO concentration.₃^– level.

Causes of Anion Acidosis

• ketoacidosis
• lactic acidosis
• kidney failure
• toxic consumption

• lack of bicarbonate through the digestive tract or kidneys
• impaired renal excretion

Signs and symptoms of anionic acidosis

Mild acidosis is frequently asymptomatic, but symptoms and signs suggestive of high anion gap acidosis may include:

• nausea
• vomiting
• bad mood
• hyperpnea (long, deep breaths at a traditional rate)
• tiredness
• cardiac dysfunction with hypotension, shock, ventricular arrhythmia

Diagnosing the Cause of High Anion Gap Acidosis

The reason for high anion gap acidosis could also be obvious, as in diabetic ketoacidosis, hypovolemic shock, or missed hemodialysis. Other data helpful in determining the cause include arterial blood gases (ABG), serum electrolytes, lactate, and possible toxins. Normal anion gap with low HCO₃^– (< 24 mEq/l) and high serum chloride levels indicate metabolic acidosis with an uninterrupted anion gap (hyperchloremic). If high anion gap acidosis is present, the delta coefficient is calculated to assist determine the cause. This coefficient compares the change (or delta) within the anion gap to the change in bicarbonate levels. Winters’ formula can be used to find out whether respiratory compensation is going on or whether a second acid-based disorder is going on. This formula calculates the expected CO₂ level based on bicarbonate level.

• Delta ratio = Delta anion gap/Delta HCO₃^– = [AG -12] ÷ [24 – HCO₃^–]
• Winter Formula: PCO₂ = (1.5 x HCO3)₃^–) + 8 ± 2

Treatment of high anion gap acidosis

Treatment is directed at reversing the cause. Hemodialysis is required for renal failure and sometimes for ethylene glycol, methanol, or salicylate poisoning. When metabolic acidosis is because of lack of bicarbonate (as in normal anion gap acidosis), bicarbonate therapy is frequently secure and effective. However, sodium bicarbonate therapy for prime anion gap acidosis is controversial and is frequently used only in cases of severe metabolic acidosis, when bicarbonate may be very low and pH is below 7.1 (Emmett & Szerlip, 2023).

Anion Gap Acidosis Mnemonics

Here are some helpful suggestions to recollect the causes of high anion gap acidosis.
The hottest mnemonics include:

• • Ketoacidosis
  • Uraemia
  • Salicylate poisoning
  • Methanol
  • Aldehyde
  • Lactate
  • Ethylene glycol
• • Methanol
  • Uraemia
  • Diabetes
  • Paraldehyde
  • Iron/Isoniazid
  • Lactate
  • Ethylene glycol
  • Salicylate

The newer mnemonic takes under consideration recent anion gap-generating organic acids and precursors which have been recognized in recent times. It also replaces paraldehyde, which has grow to be extremely rare (Mehta, Emmett, & Emmett, 2008).

• • Glycols
  • Oxoproline
  • L-lactate
  • D-lactate
  • Methanol
  • Aspirin
  • Renal failure
  • Ketoacidosis

Many times, when an obvious reason for anion gap acidosis can’t be identified, an expanded differential diagnosis will be helpful. Therefore, a modified mnemonic CUTE DIMPLES (Azim et al., 2023) will be used.

• • Cyanide
  • Uraemia
  • Toluene
  • Ethylene glycol
  • Diabetic ketoacidosis
  • Isoniazid
  • Methanol
  • Propylene glycol
  • Lactic acidosis
  • Ethanol
  • Salicylates

How to make use of knowledge in regards to the anion gap in clinical practice?

In the hospital setting, chances are you’ll hear the phrase “the anion gap is closed.” This often refers to a patient admitted to the hospital with ketoacidosis because of uncontrolled diabetes. Typically, intravenous fluids and an insulin drip are given until the gap closes, after which a maintenance regimen will be began. In what other cases have you ever heard a discussion a couple of patient’s anion gap? Have you ever had to make use of this calculation?

Anion Gap Acidosis References

Albert, M. S., Dell, R. B., and Winters, R. W. (1967). Quantitative shift of acid-base balance in metabolic acidosis., (2), 312–322. https://doi.org/10.7326/0003-4819-66-2-312

Azim, A., Hu, B., Gilligan, S., Sarwal, A., Hartsell, S., Pandya, V., and Raphael, K. L. (2024). How I assess high anion gap metabolic acidosis. , (4), 525–527. https://doi.org/10.2215/CJN.0000000000000381

Emmett, M. & Szerlip, H. (2023, September 8). Approach to the adult with metabolic acidosis. https://www.uptodate.com/contents/approach-to-the-adult-with-metabolic-acidosis

Gabow PA (1985). Disorders related to an altered anion gap. , (2), 472–483. https://doi.org/10.1038/ki.1985.34

Kraut, J. A. and Madias, N. E. (2007). The anion gap in serum: its applications and limitations in clinical medicine. , (1), 162–174. https://doi.org/10.2215/CJN.03020906

Mehta, A. N., Emmett, J. B., and Emmett, M. (2008). GOLD MARK: an anion gap mnemonic for the twenty first century. , (9642), 892. https://doi.org/10.1016/S0140-6736(08)61398-7

Rastegar A. (2007). Application of DeltaAG/DeltaHCO3- index within the diagnosis of mixed acid-base imbalance. , (9), 2429–2431. https://doi.org/10.1681/ASN.2006121408