Determining the cause of a metabolic acidosis that lacks a serum<unk> <unk>  often depends on determining whether the kidney is appropriately excreting acid. The<unk>  is an 'artificial' and calculated measure that is representative of the unmeasured ions in<unk> . Usually the most important unmeasured ion in<unk>  is NH4+ since it is the most important form of acid excretion by the kidney.<unk>  NH4+ is difficult to measure directly, but its excretion is usually accompanied by the<unk>  chloride. A negative<unk>  can be used as evidence of increased NH4+ excretion. In a metabolic acidosis without a serum<unk> <unk> : * A positive<unk>  suggests a low<unk> ry NH4+ (e.g. renal tubular acidosis). * A negative<unk>  suggests a high<unk> ry NH4+ (e.g. diarrhea).
Urine anion gap
Urine osmolality
Osmol gap
Plasma osmolality
Serum chloride
Sucrose gap
Urine sodium
Blood urea nitrogen