Serum anion gap revisited: a verified reference interval for contemporary use

Area of Science:

• Clinical Chemistry
• Acid-Base Balance
• Diagnostic Markers

Background:

• The anion gap (AG) is crucial for evaluating acid-base disorders.
• Historically accepted AG reference intervals may require revalidation due to evolving analytical techniques.

Purpose of the Study:

• To establish a current reference interval for the anion gap (AG) using modern laboratory methods.
• To validate the existing AG reference range for clinical application.

Main Methods:

• Blood samples from 284 healthy volunteers were analyzed in an accredited laboratory.
• Anion gap (AG) was calculated using the formula: [Na+] - [Cl-] - [HCO3-].
• Reference intervals were determined using the 2.5th-97.5th percentiles.

Main Results:

• The determined reference interval for AG was 10-18 mmol/L (99% confidence).
• Median AG was 13 mmol/L, consistent with the established reference interval.
• Minor AG variations were noted across sex, race, obesity, and albumin levels, but did not alter the overall reference range.

Conclusions:

• The AG reference interval of 10-18 mmol/L remains valid for laboratories with comparable electrolyte reference ranges.
• Current laboratory techniques did not yield lower AG values than anticipated.
• The median AG of 13 mmol/L is suitable for distinguishing between gap, non-gap, and mixed acid-base disorders.