Do you still use the urinary anion gap to estimate renal ammonium excretion in patients with a non-anion gap metabolic acidosis, given its limitations?

Yes, I do, but especially as a teaching tool to help understand the make-up of urine in different clinical scenarios. Of course, a urine NH4+ would make this all so much easier, but I believe that the UAG is usually still of value in the evaluation of a NAGMA.

The Achilles heel of it, of course, is that if there are increased unmeasured anions in the urine, you will have a positive urine anion gasp, NOT because of low unmeasured cation NH4+, but because of the high unmeasured anions. But having unmeasured anions in the urine are not typical, limited to DKA, antibiotics, etc. Your average patient seen in your practice with an unexplained NAGMA, the UAG, I think, is still valuable. I still look at the UpH too, even though it may be limited. L...

Yes, I still use the urine anion gap (UAG) in clinical practice. While its limitations are well recognized, most hospitals currently lack the capability to directly measure urinary ammonium. It would be preferable to measure NH4+ if this were available, however, I do not think we should completely throw out UAG. The data demonstrating poor correlation between UAG and urinary NH4+ primarily come from large patient cohorts analyzed by Litholink. For example, the study by Uribarri et al., PMID 35810828 included patients without metabolic acidosis, limiting its relevance in patients with acidosis, where correlation is most defined as in the original description by Dan Batlle in NEJM in 1988. In the appropriate clinical context, specifically in ...

I use both urinary anion gap and urinary osmolal gap to estimate renal ammonium excretion in patients with a non-anion metabolic acidosis. In clinical settings, in which ammonium is excreted with a non-chloride anion, the urinary osmolal gap will be more reliable in estimating renal ammonium excretion.

Yes, I still use the urine anion gap - I like to use it for teaching purposes, but also it is sometimes easier to obtain. Even at our institution, urine ammonia is a send out and can take at least 48 hours to come back.

No, I do not use the urinary anion gap to estimate urinary ammonium since it has been demonstrated that the urinary anion gap does not estimate urinary ammonium (DOI: Uribarri & Oh, PMID 33769949, DOI: Uribarri et al., PMID 35810828). However, since urinary anion gap is positive in renal acidosis (as it is normally in the great majority of healthy people on a Western type of diet) and happens to become negative in the presence of significant diarrhea (volume depletion decreases urinary Na excretion), I tend to pay attention to the urinary anion gap in cases of hyperchloremic metabolic when I am looking for diagnostic clues (but not because I want to estimate urinary ammonium, which would be wrong).

Thanks to all the erudite answers from the experts above.

Please also see the recent article by Battle et al., PMID 40279177.