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    Anion Gap

    Evaluates states of metabolic acidosis.


    We now have an ABG Analyzer to help with acid-base analysis as well.

    When to Use
    Why Use

    Determining if a patient's acidosis also has an elevated anion gap.

    Unmeasured proteins (e.g. immunoglobulins in patients with monoclonal gammopathies or myeloma) may lead to a paradoxically normal anion gap. 

    Anion gap acidoses have a very different differential diagnosis than non-gap acidoses.



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    Creator Insights


    Anion Gap Metabolic Acidosis: MUDPILERS

    • Methanol

    • Uremia

    • DKA/alcoholic KA

    • Paraldehyde

    • Isoniazid

    • Lactic acidosis

    • Etoh/ethylene glycol

    • Rhabdo/renal failure

    • Salicylates

    Non-Anion Gap Acidosis: HARDUPS

    • Hyperalimentation

    • Acetazolamide

    • Renal tubular acidosis

    • Diarrhea

    • Uretero-pelvic shunt

    • Post-hypocapnia

    • Spironolactone

    Acute Respiratory Acidosis (Chronic Respiratory Acidosis = COPD/restrictive lung dz): any hypoventilation state

    • CNS depression (drugs/CVA)

    • Airway obstruction

    • Pneumonia

    • Pulmonary edema

    • Hemo/pneumothorax

    • Myopathy

    Metabolic Alkalosis: CLEVER PD

    • Contraction

    • Licorice

    • Endo (Conn's, Cushings, Bartter's)

    • Vomiting

    • Excess alkali

    • Refeeding alkalosis

    • Post-hypercapnia

    • Diuretics

    Respiratory Alkalosis: CHAMPS (think speed up breathing)

    • CNS disease

    • Hypoxia

    • Anxiety

    • Mech ventilators

    • Progesterone

    • Salicylates/sepsis


    Anion gap, mEq/L = sodium, mEq/L - (chloride, mEq/L+ bicarbonate, mEq/L)

    Albumin corrected anion gap, mEq/L = anion gap + [ 2.5 × (4 - albumin, g/dL) ]

    Delta gap, mEq/L = anion gap - 12*

    Albumin corrected delta gap, mEq/L = albumin corrected anion gap - 12

    Delta ratio = delta gap / (24 - bicarbonate, mEq/L)

    Albumin corrected delta ratio = albumin corrected delta gap / (24 - bicarbonate, mEq/L)

    *Normal anion gap.

    Facts & Figures


    Delta ratio



    Hyperchloremic normal anion gap acidosis


    High AG & normal AG acidosis

    1 to 2

    Pure anion gap acidosis

    Lactic acidosis: average value 1.6

    DKA more likely to have a ratio closer to 1 due to urine ketone loss


    High AG acidosis and a concurrent metabolic alkalosis or a pre-existing compensated respiratory acidosis


    Dr. Man S. Oh

    About the Creator

    Man S. Oh, MD, is a professor of medicine and the director of fluid and electrolytes in the Department of Nephrology at SUNY Downstate Medical Center.

    To view Dr. Man S. Oh's publications, visit PubMed

    About the Creator
    Dr. Man S. Oh