Anion gap - Interpretation
Anion gap is most commonly performed for patients who present with altered mental status, unknown exposures, acute renal failure, and acute illnesses. Can some one help me interpret the values obtained?
@francis-jacob he anion gap can be defined as low, normal, or high. Laboratory error always needs to be ruled out first if the clinical picture does not correlate with the findings. Thus, if the results are questionable, re-assessing the electrolytes is the encouraged first step.
Certain errors in collection can interfere with the ions of measured electrolytes that are used to calculate the anion gap. This can include timing, dilution, renal disease, and small sample size. For example, delays in processing the collected sample results in continued leukocyte cellular metabolism, which then causes an increase in bicarbonate levels.
If the anion gap is found to be high, other tests such as urine ketones, serum ketones (beta-hydroxybutyrate), serum lactic acid, urine drug screen, serum drug screen, salicylate level, and creatinine kinase level should also be performed to diagnose the etiology of the anion gap acidosis.
The urine anion gap is either positive or negative and can be used when the causes of normal anion gap acidosis are unclear. A positive urine anion gap is seen in conditions of type 1 and type 2 renal tubular acidosis versus almost every other cause of normal anion gap acidosis (diarrhea). The limiting factor of urine anion gap equation is that it is valid only if the urine sodium level is less than 20mEq/L.
A decreased anion gap (< 6 mEq/L) may suggest the following :
Plasma cell dyscrasia
A normal anion gap (6-12 mEq/L) may indicate the following:
Loss of bicarbonate (ie, diarrhea)
Recovery from diabetic ketoacidosis
Ileostomy fluid loss
Carbonic anhydrase inhibitors (acetazolamide, dorzolamide, topiramate)
Renal tubular acidosis
Arginine and lysine in parenteral nutrition
An elevated anion gap (>12 mEq/L; “mud pilers”) may indicate the following :
Ethanol ethylene glycol