| Feature | Type 1 (Distal) | Type 2 (Proximal) | Type 4 (Hypoaldo) |
|---|---|---|---|
| Defect | Cannot secrete Hโบ in collecting duct | Cannot reabsorb HCOโโป in proximal tubule | โ Aldosterone effect โ โ Hโบ/Kโบ secretion |
| Serum Kโบ | โ Hypokalemia | โ Hypokalemia | โ Hyperkalemia |
| Urine pH | > 5.5 (cannot acidify) | < 5.5 (can acidify once bicarb threshold exceeded) | < 5.5 |
| Serum HCOโโป | Can be very low (< 10) | Usually 12โ20 (self-limited) | Usually > 15 (mild) |
| Associations | Sjรถgren, SLE, nephrocalcinosis, kidney stones | Fanconi syndrome, multiple myeloma, carbonic anhydrase inhibitors | Diabetes (#1), ACEi/ARBs, K-sparing diuretics, adrenal insufficiency |
| Treatment | Oral NaHCOโ 1โ2 mEq/kg/day | Oral NaHCOโ (high doses needed) + thiazide | Fludrocortisone (Florinef), low-K diet, loop diuretics |
| Step | Question | Answer | Interpretation |
|---|---|---|---|
| 1 | Is the anion gap normal? | AG <=12 | Confirmed NAGMA. Proceed |
| 2 | Urine anion gap? | Negative (UCl > UNa + UK) | GI loss (diarrhea). Stop here |
| 3 | Urine anion gap? | Positive (UCl < UNa + UK) | RTA. Proceed to classify |
| 4 | Serum K+? | Hyperkalemia (>5.0) | Type 4 RTA. Check aldosterone/renin, medications |
| 5 | Serum K+? | Hypokalemia (<3.5) | Type 1 or Type 2. Check urine pH |
| 6 | Urine pH? | >5.5 | Type 1 (Distal). Check for stones, autoimmune |
| 7 | Urine pH? | <5.5 | Type 2 (Proximal). Check for Fanconi, myeloma |
| Feature | Type 1 (Distal) | Type 2 (Proximal) | Type 4 (Hypoaldo) |
|---|---|---|---|
| Bicarb dose | Low (1-2 mEq/kg/day) | High (10-15 mEq/kg/day) | Usually not needed |
| Why? | Distal tubule cannot secrete H+, but proximal is intact so bicarb is retained | Proximal tubule wastes bicarb above lowered threshold, requiring massive replacement | Acidosis is mild (HCO3 usually >15) |
| K+ management | KCl supplementation (bicarb worsens hypoK) | KCl supplementation (bicarb worsens hypoK) | RESTRICT K+. Treat hyperK first |
| Unique therapy | Potassium citrate (prevents stones + corrects acidosis) | Add thiazide (volume contraction enhances proximal reabsorption) | Fludrocortisone 0.1 mg daily. Loop diuretics for K+ excretion |
| Stop offending drugs | Amphotericin B, lithium, toluene | Carbonic anhydrase inhibitors (acetazolamide), tenofovir, cisplatin | ACEi/ARBs, K-sparing diuretics, TMP-SMX, NSAIDs, heparin |
| Drug | Dose | Type |
|---|---|---|
| Sodium Bicarbonate | 1โ2 mEq/kg/day (Type 1); 10โ15 mEq/kg/day (Type 2) | Types 1 & 2 |
| Potassium Citrate | 20โ40 mEq BID-TID | Type 1 -corrects acidosis AND prevents stones |
| Fludrocortisone (Florinef) | 0.1 mg PO daily | Type 4 -mineralocorticoid replacement |
| Furosemide (Lasix) | 20โ40 mg PO daily | Type 4 -enhances Kโบ excretion |
| Hydrochlorothiazide (Microzide) | 12.5โ25 mg daily | Type 2 -volume contraction increases proximal HCOโโป reabsorption |
Patient: 32F with Sjรถgren syndrome, fatigue, muscle weakness. BMP: K 2.8, HCOโ 12, AG 10 (normal). Urine pH 6.2.
Diagnosis: Type 1 (Distal) RTA.
Key findings:
Treatment: NaHCOโ 1โ2 mEq/kg/day + KCl supplementation. Monitor for nephrocalcinosis.
Patient: 65M with type 2 diabetes on lisinopril. BMP: K 6.1, HCOโ 18, AG 10. Urine pH 5.0.
Diagnosis: Type 4 RTA.
Key findings:
Treatment: Stop lisinopril, low-K diet, fludrocortisone if persistent hyperkalemia.
Patient: 8-year-old with failure to thrive, rickets, glycosuria with normal blood glucose, aminoaciduria.
Diagnosis: Fanconi syndrome โ Type 2 (Proximal) RTA.
Key findings:
Workup: Evaluate for underlying cause, in children, cystinosis is the most common cause. In adults, consider multiple myeloma (light chains), tenofovir, cisplatin.