Historically, foamy urine is considered a warning sign for probable kidney disease. Nephrologists and urologists traditionally refer to it as a marker of proteinuria. Upon history and physical examination, many clinicians ask whether the patient has noticed foamy urine, and some even document a lack of it as a significant negative finding.

I travel frequently, and upon going to public bathrooms in different domestic airports I cannot help but noticing residues of foamy urines in many urinals. Indeed, my anecdotal observation of frequent urinary bubbles in public bathrooms is not restricted to the airports. I also have noticed it in the bathrooms of restaurants, coffee shops, and even the bathrooms the staff use at my workplace.

Am I observing a fast-growing epidemic of proteinuria in an increasingly unhealthy nation with metabolic syndrome and chronic kidney disease?

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Foamy urine can also be caused by factors other than protein in the urine. Rapid urination can create bubbles in the urine, so maybe people in airport bathrooms are in a rush, but then the foam should not persist for more than a few seconds, so that when a curious visitor like me inspects the urinals, I should really not see long-lasting foams.

Concentrated urine in hot weather can also lead to foamy urine, but the foamy urines I have observed in public bathrooms are not restricted to summer time. Kidney stones can lead to foamy urine as can urinary tract infections by virtue of pyuria.

Similarly, we may observe frothy urine when there is leukocyturia, for example, due to acute interstitial nephritis or prostatitis. Would other bladder or prostate disorders also lead to foamy urine? Other rare causes of foamy urine include vesico-intestinal fistula such as in Crohn’s disease or ulcerative colitis. The presence of semen as a result of retrograde ejaculation or even after sexual intercourse may lead to foamy urine.

Upon looking up this “foamy urine” in PubMed and Google Scholar I was disappointed to find very limited literature about this topic and essentially no systemic study about causes and consequences of foamy urine. There are many unanswered questions.

For example, is the size or intensity of foam a helpful feature for the differential diagnoses? Would the presence of micro-hematuria confound the appearance of foamy urine? Can different types of protein lead to different foam formation or threshold? Is a simple urinalysis the first step in the workup of foamy urine?

I think nobody really knows answers to any of these questions. I always thought that any degree of proteinuria can cause foamy urine. However, it is not clear what minimum amount is needed. Undoubtedly, more research is needed.