Serum Anion Gap (AG)
The serum anion gap represents the difference between measured cations (Na+) and measured anions (Cl- and HCO3-), screening for metabolic acidosis and unmeasured organic anions.
Standard vs. Optimal Reference RangesmEq/L
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
4 - 12 mEq/L (Calculated: Na - [Cl + HCO3])
General reference distribution across unselected commercial populations.
6 - 10 mEq/L
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Unmeasured serum anions primarily consist of negatively charged albumin, phosphate, and sulfate. In pathological states, ketoacids, lactate, or toxins expand the gap.
Differential Diagnosis
Elevated Levels (AG High)
- •Diabetic or alcoholic ketoacidosis
- •Lactic acidosis (hypoperfusion, metformin)
- •Uremic renal failure
- •Toxic ingestions (Salicylates, Methanol, Ethylene glycol)
Low Levels (AG Low)
- •Severe hypoalbuminemia (albumin accounts for ~75% of normal anion gap)
- •Multiple myeloma (monoclonal cationic immunoglobulins)
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Maintain standard hydration status prior to venipuncture; acute hypovolemia or hemoconcentration artificially elevates concentrations. Avoid heavy resistance training and high-protein meals (especially cooked red meat) for 24 hours prior if testing serum creatinine. Ensure tourniquet time does not exceed 60 seconds to avoid pseudohyperkalemia or hemoconcentration of electrolyte fractions.
Reflexive Testing Protocol:
- Simultaneous Serum Cystatin C testing to calculate composite CKD-EPI Creatinine-Cystatin C eGFR equation
- Spot Urine Albumin-to-Creatinine Ratio (uACR) to detect subclinical glomerular endothelial leak
- Renal duplex ultrasonography to assess bilateral kidney dimensions, cortical echogenicity, and resistive index
- Fractional Excretion of Sodium (FENa) and Urea (FEUrea) to differentiate prerenal azotemia from intrinsic acute kidney injury
- Serum and urine protein electrophoresis (SPEP/UPEP) if tubular injury or monoclonal gammopathy is suspected
Clinical Citations & Primary Literature (1)
- [1]Clinical Approach to Acid-Base Disorders and the Serum Anion Gap - New England Journal of Medicine (2021). PMID: 33761208
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Serum Anion Gap (AG) into overall healthspan optimization.