The Urinary Anion Gap (UAG)

Cations in urine:

• Na+
• K+
• Ca++
• Mg++
• NH4+ (very hard to be measured)

Anions in urine:

• Cl-
• HCO3-
• sulphate
• phosphate
• organics anions

Measured: Na, K, Cl

URINARY ANION GAP     =    Na   +    K    -   Cl

Interpritation:

• Negative UAG: loss of base via the kidney
• Positive UAG: loss of base via bowel

In acidosis UAG should be  Negative and  In alkalosis  positive if kidney appropriately compensating.