Sterile Pyuria: Horses for Courses

Open most microbiology textbooks (particularly the older ones) and you will find tuberculosis high on the differential diagnosis of sterile pyuria.

This might be true in some parts of the world, but I suspect in a lot of places, and certainly where I work in New Zealand, renal tuberculosis is an extremely rare cause of sterile pyuria.

"Pyuria"
“Pyuria”

I would estimate about 1 in 1000 cases of sterile pyuria are due to TB here in NZ. There are much more common causes such as recently treated UTI, contamination with vaginal leucocytes secondary to chlamydia, candida infection, infection due to fastidious organisms etc etc.

GPs often reflexively order 3 Early Morning Urines for mycobacterial culture when they see a report suggesting sterile pyuria (because of those textbooks). In some areas of the world this might be appropriate, but in our lab in New Zealand, we like to see either repeated sterile pyuria results on the same patient or strong supporting clinical information before even accepting urines for TB culture.

Along the same lines if you have a young sexually active adult with sterile pyuria with no obvious cause, then excluding chlamydia should be at the forefront of your mind, and an appropriate comment to suggest this should always be added to such reports.

Horses for Courses….

Michael

I am away at a virus conference for the next few days…..

2 thoughts on “Sterile Pyuria: Horses for Courses

  1. Good posting Michael thanks!

    There is a useful review of sterile pyuria in the NEJM this week

    I think a common misconception is that ‘pyuria’ necessarily means an excess of white cells. In reality, nearly all labs use phase contrast microscopy to recognise white cells. Renal tubular epithelial cells appear the same under PC. Thus patients with interstitial nephritis , say from a drug reaction or other cause will also have ‘pyuria’. I’m uncertain whether automated cell counters also confuse these two!

    Another common circumstance for pyuria is in patients managed with indwelling catheters where perhaps low grade bladder inflammation, often associated with bacteriuria is the cause.

    Pyuria is also exceedingly frequent in asymptomatic bacteriuria in the elderly and others in my experience.

    1. Thanks for your comments John. The urologists and GPs were happy with our decision to only accept mycobacterial culture on patients with recurrent/persistent sterile pyuria. It has also decreased unnecessary testing and increased relative yield. A few phonecall queries to start with but policy well embedded now..

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