نظرة سريرية عامة

The serum anion gap and delta ratio is a bedside decision-support calculation used to standardize a defined part of clinical assessment. They characterize unmeasured ions and help identify mixed metabolic acid-base disorders when electrolytes are measured together. The result should be interpreted with the patient’s presentation, baseline function, serial observations, laboratory method, medication exposure, and the protocol used by the treating institution. It is an aid to communication and risk stratification rather than an independent diagnosis or treatment order.

Enter contemporaneous values and confirm every unit before calculating. When physiology is changing, repeat assessment and prioritize the clinical trajectory over a single number. Document the input values alongside the result so another clinician can reproduce the calculation and recognize assumptions. Thresholds describe populations and do not remove the need to investigate discordant symptoms, examination findings, imaging, or biomarkers.

دواعي الاستخدام

• Evaluation of suspected metabolic acidosis
• Detection of mixed metabolic acid-base disorders

القيود والسلامة

Normal AG varies by laboratory; albumin is a major unmeasured anion, and delta ratio is not meaningful without a high-gap metabolic acidosis. Validation cohorts, case mix, prevalence, and treatment era affect observed event rates. Pregnancy, extremes of age or body composition, critical illness, and major comorbidity may reduce transportability unless specifically represented in the original model. Do not extrapolate beyond the stated population or substitute this estimate for a validated local pathway.

Before acting, check for missing data, measurement error, competing diagnoses, contraindications, and time-sensitive emergencies. A low-risk label never overrides clinician concern; a high-risk label does not prove the target condition. Discuss consequential decisions with the appropriate senior or specialty team and use current regional guidance.

• Interpret only with simultaneous laboratory values and clinical context
• Reference intervals vary by laboratory and analyzer

المعادلة

AG = Na − (Cl + HCO₃). Corrected AG = AG + 2.5 × (4 − albumin g/dL). Delta ratio = (corrected AG − 12) / (24 − HCO₃)

تفسير النتائج

• Corrected AG above local upper limit — High-gap process: Unmeasured anions may be present. Evaluate lactate, ketones, renal failure, toxins, and context.
• Delta <0.4 / 0.4–0.8 — Hyperchloremic component: Pure normal-gap or mixed acidosis may coexist. Review chloride load, GI and renal bicarbonate loss.
• Delta 0.8–2 / >2 — High-gap / mixed alkalosis: Typical high-gap or concurrent alkalosis/respiratory acidosis. Confirm with blood gas and clinical assessment.

المراجع

1. Kraut JA, Madias NE. Serum anion gap: uses and limitations.
2. Figge J, et al. Anion gap and hypoalbuminemia.

الأسئلة الشائعة

Why correct for albumin?

Low albumin lowers the expected anion gap and can conceal an accumulation of unmeasured acids.

Should potassium be included?

This calculator uses the common equation without potassium; compare with the matching laboratory reference interval.

When is delta ratio invalid?

It is not useful without a raised anion gap and becomes unstable when bicarbonate is near or above 24 mmol/L.