Table 1.

Characteristics of normal anion gap (AG) metabolic acidosis diseases

	Serum bicarbonate, mEq/L	Plasma K+	Ca2+ excretion	Urine AG mEq/L	Urine osmolol gap, mosm/kg in metabolic acidosis	Urinary NH+4, mEq/day	Minimal urine pH	Ability to acidify urine in response to acidemia	Urine-blood pCO2, mm Hg	Comment
Health	Normal	Normal	Normal	+20 to +90	10 – 100	30–40	4.5 – 6	Yes	>30
Severe diarrhea	<24	Low	Normal	–20 to −50	>200	High	>5.5	Yes
Toluene/hippurate	<24	Low	Normal	Positive	>200	High		Yes
Defective CA II activity/proximal RTA (type 2)	12 – 20	Low/normal	Normal	Negative −20 to −50	>150	Normal	<5.5	Yes		Urine pH >6.5 during early phase with bicarbonaturia
Fanconi syndrome/proximal RTA (type 2)	12 – 18	Low	↑	Negative −20 to −50	>150	Normal	<5.5	Yes		Hypophosphatemia/phosphaturia, hypouricemia/hyperuricosuria renal glucosuria (glucosuria with a normal serum glucose concentration), aminoaciduria
Hypokalemic distal RTA (type 1)	10 – 20	Low	↑	Positive	<150 (usually <50 – 100)	Low	>5.5 (often >6.5)	No	<30
Back diffusion	8 – 15	Low	?	Positive	?	Low		No
Hyperkalemic distal RTA (voltage-dependent RTA)	8 – 15	High	Normal or ↑	Positive	<150(usually <50 – 100)	Low	>5.5(often >6.5)	No
RTA type 3	Low	Low	↑			Low	>5.5	No
RTA type 4	16 – 22	High	Normal	Positive	<150(usually <50 – 100)	Low	<5.5	Yes		Often increased creatinine

CA, carbonic anhydrase; RTA, renal tubular acidosis; urine-blood pCO₂, urine-blood pCO₂ after bicarbonate loading.