Our wonderful nose has the capacity to detect more than a trillion scents. Frequently bedside hospital nurses suspect C. diff diarrhea in their patients based on 💩 smell. A study in 2013 (although very small) showed only 45% accuracy of nurse’s smell-based ability in detecting C. diff infection, irrespective of years of experience, so it’s a coin toss. Bad-smelling urine is another common situation where nurses alert providers about a possible infection – is that reliable? Let’s look at how our olfactory powers stack up in diagnosing UTIs!
A study in 2004 evaluted smells of incontinent pads of nursing home residents and found that the “smell of urine in incontinence pads may be an absent or misleading symptom for UTIs“. A comprehensive observation study on the elderly published in 2009 compared various known UTI symptoms for their ability to predict a UTI based on culture and found that 3 features – dysuria, ‘change in character’ of urine, and altered mentation – were the most predictive. A combination was even more predictive than a single feature. The ‘change in character’ included changes in odor, color & bloody urine but unfortunately did not report a split on how many of those were odor-related. Another Belgian nursing home study looking at various clinical parameters for suspecting UTIs found only 11% actually had UTIs. The only strong predictors were dysuria & suprapubic pain. Interestingly, as this table shows, foul smell was the most common reason to suspect UTI by Nurses & CNAs. However, in a study of younger Asian women published in 2019 (60% of women< 65 yrs. age), foul-smelling urine was one of the most predictive of UTIs with > 80% specificity and > 70% positive predictive value!
So how do we make sense of all this?
Besides an infection, urine can take on a foul odor also from dehydration (concentrated urine), normal transient bacteriuria, bacterial decomposition in incontinent urine, and the effect of some foods & meds. Conditions of dehydration, transient bacteriuria, incontinence & being on multiple meds are much more common in the elderly, and hence foul odor as a predictor for UTI gets less specific with age. Also, urine infections don’t always result in foul smell 🤷🏽♀️
💡 A new change in urine smell could be from multiple causes. In elderly women, a foul smell of urine alone is a poor clinical predictor of UTIs, but is a better predictor when combined with additional symptoms ( altered mentation, dysuria, change in frequency/urgency, etc) . In younger women, a new change in the smell of urine can perhaps be a stronger indicator of UTIs.
P.S: Not all hope is lost about urine smells and UTIs – specific bacteria can result in specific chemicals called VOCs (Volatile Organic Compounds) that are responsible for smells that our noses may not pick & differentiate. Sensitive devices such as the e-Nose are emerging ways to screen for UTIs.
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