Metabolic Acidosis Differential Diagnoses
- Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FACP, FASN more...
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| Characteristics | Proximal (Type 2) | Distal (Type 1) | Type 4 |
| Primary defect | Proximal HCO3 - reabsorption | Diminished distal H+ secretion | Diminished ammoniagenesis |
| Urine pH | < 5.5 when serum HCO3 - is low | >5.5 | < 5.5 |
| Serum HCO3 - | >15 mEq/L | Can be < 10 mEq/L | >15 mEq/L |
| Fractional excretion of HCO3 - (FEHCO3) | >15-20% during HCO3 - load | < 5% (can be as high as 10% in children) | < 5% |
| Serum K+ | Normal or mild decrease | Mild-to-severe decrease* | High |
| Associated features | Fanconi syndrome | ... | Diabetes mellitus, renal insufficiency |
| Alkali therapy | High doses | Low doses | Low doses |
| Complications | Osteomalacia or rickets | Nephrocalcinosis, nephrolithiasis | ... |
| *K+ may be high if RTA is due to volume depletion. | |||

