Table 2 Differential diagnosis for metabolic acidosis (decreased SID)

Renal tubular acidosis:

Nonrenal:

urine SID (Na⁺ + K⁺ – Cl) > 0

urine SID (Na⁺ + K⁺ – Cl^-) < 0

Distal (type I): urine pH >5.5

Gastrointestinal: diarrhea, small

bowel/pancreatic drainage

Proximal (type II): urine

pH <5.5/low serum K⁺

Iatrogenic: parenteral nutrition,

saline, anion exchange resins

Aldosterone deficiency (type IV):

urine pH <5.5/high serum K⁺