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Anion gap (corrected and delta–delta)

Estimates unmeasured plasma anions to classify metabolic acidosis as high- or normal-anion-gap and reveal associated disorders using the delta ratio.

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Method · Limits of application

AG without K+; Figge 1998 correction 2.5×(4−albumin); delta AG reference 12/delta HCO₃ reference 24

The reference value for the anion gap depends on the laboratory method and varies between individuals. Abnormal values do not identify a single cause and may reflect laboratory error. The ΔAG/ΔHCO3 ratio should not be used alone to identify mixed acid–base disorders; additional clinical and laboratory data are needed. Albumin correction and the reference values used in the calculation require checking against the sources for the variant.

Conditions of use

Check the population, units, inclusion and exclusion criteria, and version in the original source. A result alone does not establish a diagnosis, discharge decision or prescription.

Documented parameters

Sodium · mEq/L
Chloride · mEq/L
Bicarbonate · mEq/L
Albumin · g/dL

5/5 reference cases checked. Numerical tests are not clinical validation.

Sources and documentation

Documented formula

Transcribed from the source or a recorded revision; this is not a clinical recommendation.

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻).

Albumin-corrected = AG + 2.5 × (4.0 − albumin in g/dL).

Delta ratio = (AG − 12) ÷ (24 − HCO₃⁻).

References

Identifier: anion-gap

Original clinical content: Brazilian Portuguese.

Method version

AG without K+; Figge 1998 correction 2.5×(4−albumin); delta AG reference 12/delta HCO₃ reference 24

anion-gap@native-2026-10-03+89e6f9237bb1

Source for the active edition

The bibliographic edition identifies the source. By itself, it proves neither full conformity of the formula nor clinical approval.

Synthetic cases checked (5)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

Sodium: 140 mEq/L
Chloride: 104 mEq/L
Bicarbonate: 24 mEq/L

{
  "na": 140,
  "cl": 104,
  "hco3": 24
}

Expected result

{
  "ag": 12
}

Actual result

{
  "ag": 12,
  "agc": 12
}

Case 2

reference-002

Inputs

Sodium: 140 mEq/L
Chloride: 115 mEq/L
Bicarbonate: 15 mEq/L

{
  "na": 140,
  "cl": 115,
  "hco3": 15
}

Expected result

{
  "ag": 10
}

Actual result

{
  "ag": 10,
  "agc": 10
}

Case 3

reference-003

Inputs

Sodium: 140 mEq/L
Chloride: 100 mEq/L
Bicarbonate: 10 mEq/L
Albumin: 4 g/dL

{
  "na": 140,
  "cl": 100,
  "hco3": 10,
  "alb": 4
}

Expected result

{
  "ag": 30,
  "agc": 30,
  "dr": 1.286
}

Actual result

{
  "ag": 30,
  "agc": 30,
  "dr": 1.2857142857142858
}

Case 4

reference-004

Inputs

Sodium: 138 mEq/L
Chloride: 108 mEq/L
Bicarbonate: 18 mEq/L
Albumin: 2 g/dL

{
  "na": 138,
  "cl": 108,
  "hco3": 18,
  "alb": 2
}

Expected result

{
  "ag": 12,
  "agc": 17,
  "dr": 0.833
}

Actual result

{
  "ag": 12,
  "agc": 17,
  "dr": 0.8333333333333334
}

Case 5

reference-005

Inputs

Sodium: 140 mEq/L
Chloride: 90 mEq/L
Bicarbonate: 20 mEq/L

{
  "na": 140,
  "cl": 90,
  "hco3": 20
}

Expected result

{
  "ag": 30,
  "dr": 4.5
}

Actual result

{
  "ag": 30,
  "agc": 30,
  "dr": 4.5
}

Code and reproducibility

This tool’s code on GitHub

Download code and tests

Sources, version and reproduction instructions

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.