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What’s the Difference Between FLUTD and FIC?

vet listening to a cat's chest with stethoscope
Image Credit: LightField Studios, Shutterstock
Last Updated on November 21, 2023 by Catster Editorial Team

Jen asked an interesting question in the comments section of my recent post on feline bladder infections.

Dr. Barchas, could you clarify something? Ive noticed a few times that you call what I thought was cystitis (or Feline Idiopathic Cystitis), FLUTD? This seems a bit confusing to me. I thought FLUTD (Feline Lower Urinary Tract Disease) was a term used to describe any condition of the lower urinary tract (cystitis, crystal/stones, obstruction or UTI)?

I found this on Catster:
Feline lower urinary tract disease (FLUTD) is an umbrella term for a number of conditions affecting the feline bladder and urethra including Feline Idiopathic Cystitis (FIC), urinary stones and urethral obstruction.
Also the Cornell University vet brochure about FLUTD says the same thing, that FLUTD describes a number of conditions of the feline urinary system.

I think some of these terms and conditions are confusing to people. Ive also noticed many people arent even aware that cystitis (non-bacterial inflammation of the bladder) even exists. This is a bit troubling since it is the most common urinary ailment (from everything Ive read). Many people seem to think everything is a UTI (except for crystals and stones, which are also discussed). Arent true bacterial urinary tract infections actually relatively rare in cats (unless they are older, or have diabetes, CKD or hyperthroidism diseases which dilute the urine)? And another thing is I think people need to realize how important proper diagnostics are with urinary issues. Getting a clean, uncontaminated sample through cystocentesis and examining it quickly are important since urine samples can easily be contaminated with bacteria. Also not just doing urinalysis, but a C&S is necessaryOver prescribing antibiotics is a concern, which is related to this issue.

cat poop in litterbox
Image Credit: RJ22, Shutterstock

I think it would be helpful to clarify some of these issues. Its starting to annoy me when anytime a cat has a litterbox issue, people immediately say, it could be a bladder infection or recently someone on Catster said, 99% of the time when a cat is having litterbox issues, its a UTI. Another point is that though cystitis is sometimes called idiopathic cystitis there are some factors that are known to exacerbate/if not cause cystitis and other urinary conditions, namely: 1) diet and also 2) stress. So is cystitis really idiopathic?

First, Jen, let me thank you for doing much of this post’s work for me. Your understanding of feline urinary issues is better than that of many vets!

Let’s start by clarifying the difference between three terms: feline urologic syndrome (FUS), feline lower urinary tract disease (FLUTD), and feline interstitial (or idiopathic) cystitis (FIC). Actually, there is no difference, at least in my part of the country. The three terms are interchangeable synonyms for an identical syndrome.

About 20 years ago FUS was used to describe a syndrome in which cats’ bladders and urethras became inflamed for reasons that were unrelated to bladder infection. The syndrome was often linked to crystals in the urine and an elevated urinary pH. FUS could predispose cats to bladder stones or to urinary obstruction. However, FUS was not an umbrella term; it was used only to describe the syndrome of inflammation. It did not apply to cats with UTIs, stones, or obstruction.

Since vets (especially those in teaching institutions) are prone to pedantism, some of them took issue with the phrasing of feline urologic syndrome. They thought it was too vague. The syndrome took place in the lower urinary tract (bladder and urethra), so why use a term (urologic) that described any portion of the system. Many vets therefore started calling the syndrome feline lower urinary tract disease, or FLUTD.

Many other vets were still not satisfied. They were worried that the term still was not specific enough. So, in recent years, a movement has begun (led again by vets in the Ivory Tower) to rename the syndrome FIC. I have a hunch that this name won’t stick either, since there already is confusion about what the “I” stands for.

When I use them, the three terms are absolutely interchangeable. None of them is an umbrella term. They all describe exactly the same syndrome, which is by far the leading cause of urinary problems in young cats, and which can predispose male cats to life-threatening urinary obstruction.

But, as you may have noticed, the terminology has been somewhat fluid over the years. Perhaps Cornell University is now spearheading an effort to separate the terms. FLUTD could be changed into an umbrella term, and FIC can be used to describe the syndrome of interest. I’m sure that such an effort, if it exists, will do nothing to clear up the confusion.

Jen is absolutely correct when she says that FUS/FLUTD/FIC is more common than bladder infections, except in cats with concurrent diseases such as diabetes or kidney disease. She also is absolutely correct in recommending a comprehensive work up, including a urine culture, before diagnosing a UTI.

The definitive cause of FUS/FLUTD/FIC is not known; the syndrome is therefore considered idiopathic. However, several risk factors are known. The leading risk factors are diet, stress (especially living in multiple cat households), and obesity.

Featured Image Credit: LightField Studios, Shutterstock

About the Author

Dr. Eric Barchas
Dr. Eric Barchas

Dr. Eric Barchas is a professional traveler who spends his spare time working as a full-time veterinarian; contributing to Dogster and Catster; walking, cooking, camping, and exploring the outdoors; skiing (when conditions permit); and reading Booker-shortlisted novels. In between trips Dr. Barchas lives and works in the San Francisco Bay Area with his wife, Denise, and his canine pal, Buster. His main veterinary interests are emergency and critical care, wellness, pain management and promotion of the human-animal bond. Dr. Barchas has to Dogster and Catster since May 2005. 

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