Workup for non-AG metabolic acidosis

• Evaluate history for causes (see above)

• ✓ urine anion gap (UAG) = (UNa + UK) – UCl UAG = unmeasured anions – unmeasured cations; NH4+ is primary unmeasured cation (represented by UCl). UAG is indirect assay for renal H+ excretion.

• ⊖ UAG → ↑ renal NH4+ excretion → appropriate renal response to acidemia Ddx: GI causes (diarrhea, fistulas, ureteral diversion), IV NS, ingestions

• ⊕ UAG → failure of kidneys to generate NH4+ Ddx: distal (type 1, usually ↓ K) or hypoaldo (type IV, usually ↑ K) RTA, early renal failure

• UAG unreliable in AKI/CKD, polyuria, Na depletion (UNa <20), UpH >6.5 & HAGMA (causes ⊕ UAG b/c excretion of organic anions) and less useful in prox RTA as variable. Then use UOsm gap = measured UOsm – [2×(Na+ + K+) + BUN + glc (mmol/L)]. UOsm gap <40 mmol/L indicates impaired NH4+ excretion

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• If UAG unreliable or equivocal, measure urinary pH

• ✓ urinary pH → pH < 5.5 → distal RTA pH < 5.5 with high UAG or high urinary NH4+ suggests distal RTA

• ✓ urinary pH → pH > 5.5 → proximal (type 2) RTA pH > 5.5 with high UAG or high urinary NH4+ suggests proximal (type 2) RTA

• ✓ urinary pH → pH > 5.5 → high anion gap metabolic acidosis pH > 5.5 with high UAG or high urinary NH4+ suggests high anion gap metabolic acidosis

• ✓ urinary pH → pH < 5.5 → hypoaldo RTA pH < 5.5 with high UAG or high urinary NH4+ suggests hypoaldo RTA

• ✓ urinary pH → pH < 5.5 → low anion gap metabolic acidosis pH < 5.5 with high UAG or high urinary NH4+ suggests low anion gap metabolic acidosis

• ✓ urinary pH → pH < 5.5 → metabolic acidosis with normal anion gap pH < 5.5 with high UAG or high urinary NH4+ suggests metabolic acidosis with normal anion gap

• If UAG and urinary pH unreliable or equivocal, measure plasma NH4+

• ✓ plasma NH4+ → ↑ → renal failure plasma NH4+ is marker of renal failure

• ✓ plasma NH4+ → ↓ → extrarenal NH4+ loss plasma NH4+ is marker of extrarenal NH4+ loss

• ✓ plasma NH4+ → normal → non-anion gap metabolic acidosis plasma NH4+ is marker of non-anion gap metabolic acidosis

1. Evaluate history for causes of metabolic acidosis
2. Urine anion gap (UAG) = (UNa + UK) – UCl
3. UAG = unmeasured anions – unmeasured cations; NH4+ is primary unmeasured cation (represented by UCl). UAG is indirect assay for renal H+ excretion.
4. UAG → ↑ renal NH4+ excretion → appropriate renal response to acidemia
5. UAG → failure of kidneys to generate NH4+
6. UAG unreliable in AKI/CKD, polyuria, Na depletion (UNa <20), UpH
7. If UAG unreliable or equivocal, measure urinary pH
8. Urinary pH → pH < 5.5 → distal RTA
9. Urinary pH → pH > 5.5 → proximal (type 2) RTA
10. Urinary pH → pH > 5.5 → high anion gap metabolic acidosis
11. Urinary pH → pH < 5.5 → hypoaldo RTA
12. Urinary pH → pH < 5.5 → low anion gap metabolic acidosis
13. Urinary pH → pH < 5.5 → metabolic acidosis with normal anion gap
14. If UAG and urinary pH unreliable or equivocal, measure plasma NH4+
15. Plasma NH4+ → ↑ → renal failure
16. Plasma NH4+ → ↓ → extrarenal NH4+ loss
17. Plasma NH4+ → normal → non-anion gap metabolic acidosis

窩的英文不太好

• 如果 UAG 不可靠或模棱兩可，測量尿液 pH 值

• ✓ 尿液 pH → pH < 5.5 → 遠端 RTA pH < 5.5 伴高 UAG 或高尿 NH4+ 建議遠端 RTA

• ✓ 尿液 pH → pH > 5.5 → 近端（2 型）RTA pH > 5.5 伴高 UAG 或高尿 NH4+ 建議近端（2 型）RTA

• ✓ 尿 pH → pH > 5.5 → 高陰離子間隙代謝性酸中毒 pH > 5.5 伴高 UAG 或高尿 NH4+ 提示高陰離子間隙代謝性酸中毒

• ✓ 尿液 pH → pH < 5.5 → hypoaldo RTA pH < 5.5 伴高 UAG 或高尿 NH4+ 提示低醛基 RTA

• ✓ 尿液 pH → pH < 5.5 → 低陰離子間隙代謝性酸中毒 pH < 5.5 伴高 UAG 或高尿 NH4+ 提示低陰離子間隙代謝性酸中毒

• ✓ 尿液 pH → pH < 5.5 → 代謝性酸中毒，陰離子間隙正常 pH < 5.5 伴高 UAG 或高尿 NH4+ 提示代謝性酸中毒，陰離子間隙正常

• 如果 UAG 和尿液 pH 值不可靠或模棱兩可，測量血漿 NH4+

• ✓ 血漿 NH4+ → ↑ → 腎功能衰竭 血漿 NH4+ 是腎功能衰竭的標誌

• ✓ 血漿 NH4+ → ↓ → 腎外 NH4+ 丟失 血漿 NH4+ 是腎外 NH4+ 丟失的標誌

• ✓ 血漿 NH4+ → 正常 → 非陰離子間隙代謝性酸中毒 血漿 NH4+ 是非陰離子間隙代謝性酸中毒的標誌

1. 評估代謝性酸中毒的病史 2.尿陰離子間隙（UAG）=（UNa+UK）-UCl
2. UAG = 未測量的陰離子 - 未測量的陽離子； NH4+ 是主要的未測量陽離子（以 UCl 表示）。 UAG 是腎臟 H+ 排泄的間接測定。
3. UAG → ↑ 腎臟 NH4+ 排泄 → 適當的腎臟對酸血症的反應
4. UAG → 腎臟無法產生 NH4+
5. UAG 在 AKI/CKD、多尿、Na 耗竭 (UNa <20)、UpH 中不可靠
6. 如果 UAG 不可靠或模棱兩可，測量尿液 pH 值
7. 尿液 pH → pH < 5.5 → 遠端 RTA
8. 尿液 pH → pH > 5.5 → 近端（2 型）RTA 10.尿液pH值→pH>5.5→高陰離子間隙代謝性酸中毒
9. 尿液 pH → pH < 5.5 → hypoaldo RTA 12.尿液pH值→pH<5.5→低陰離子間隙代謝性酸中毒
10. 尿液 pH → pH < 5.5 → 陰離子間隙正常的代謝性酸中毒
11. 如果 UAG 和尿液 pH 值不可靠或模棱兩可，測量血漿 NH4+
12. 血漿 NH4+ → ↑ → 腎功能衰竭
13. 血漿 NH4+ → ↓ → 腎外 NH4+ 丟失 17.血漿NH4+→正常→非陰離子間隙代謝性酸中毒