Normal Anion-Gap Acidosis (NAGMA) - Differential Diagnosis Framework and Workup



NAGMA

- Chem, ABG or VBG

- Calculate Anion Gap

- UAG and Urine osmolar gap

- UA with urine pH



Calculate Urinary Anion Gap

- Estimate urine ammonium concentration if increased or decreased in hyperchloremia

- GI 

	• Urine osmolar gap > 400

	• (+) NH4 in the urine

- Renal

	• Urine osmolar gap < 150

	• (-) NH4 in the urine



1. Chloride Intoxication

	- Normal saline infusion

	- Hyperalimentation



2. Renal Loss of HCO3

	- Renal insufficiency (GFR 20-50 ml/min)

	- Acetazolamide therapy

	- Hypoaldosteronism

	- Renal Tubular Acidosis (RTA):

		Type 1: Distal RTA:

		  • Impaired H+ secretion

		  • Urine pH > 5.5

		  • Serum K low/normal

		Type 2: Proximal RTA:

		  • Low HCO3 absorption

		  • Urine pH < 5.5

		  • Serum K: low/normal

		Type 4: Hyperkalemic RTA:

		  • Urine pH > 5.5

		  • Serum K high/normal



3. GI Loss of HCO3

	- Diarrhea

	- High output fistulas

	- Pancreatic/Biliary drainage

	- Ureteroileostomy/ureterosigmoidostomy

	- Surgical drains

	- Chronic laxative abuse

	- Villous adenoma

	- Losses via NGT tube



By Dr. Ravi Singh @rav7ks



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