urinary anion gap

Introduction

urine Na+ + urine K+ - urine Cl-

Indications

• is used as a rough approximation of urine [NH4+]

* urine chloride approximates urine [NH4+]

Reference interval

• 30-50 meq/L

Clinical significance

• a metabolic acidosis* of extrarenal orign is suggested by a large negative urine anion gap due to significant urine NH4+ excretion
• a metabolic acidosis* of renal orign is suggested by a positive urine anion gap due to minimal urine NH4+ excretion

* normal anion gap

Increases

• metabolic acidosis due to renal tubular acidosis type 1

Decreases

• a negative urinary anion gap associated with GI loss of HCO3-

More general terms

• urine chemistry test

Additional terms

• anion gap