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Urology/Sinking urine/mold spots in toilet bowl


QUESTION: Dr Leslie,

I have two questions:

1. In past couple weeks, my urine settles to the bottom of the toilet bowl instead of just turning all the water yellow -- i.e., the water at the top stays clear and the porcelain at the bottom of the bowl turns yellow. This is a new issue. Is this an indicator of proteinuria and, if not, what is the significance? I do get clumps (little floating islands) of small bubbles on water surface. They dissipate within a minute or so.

2. Unless I use bowl cleaner tablets (bleach) in the toilet tank, my toilet bowl develops small black mold spots after a few days although I flush after every use.  My wife uses a different toilet and it does not develop these spots and we do not use the bleach tablets in her toilet. How to interpret?

History -- 72-year-old wm, eGFR mid-to-high 50's for several years  diagnosed w/ Type 2 diabetes (unmedicated),  A1C level range 5.8-6.1, history of uric acid kidney stones. I take ARBs and carvedilol and amlodipine for blood pressure, PPI and Zantac for GERD, baby aspirin, Crestor, Ambien and .5 mg xanax at bedtime. Also daily vitamin/mineral, plus 1000 mg D-3, and ubiquinol.

I am concerned that the problems I've described are telling me something seriously bad is happening with my kidneys. Your comments would be appreciated.

ANSWER: Edward:

I have not encountered these types of problems and so cannot give you a definitive answer. It would be helpful if we had a formal urinalysis examination.  

I suspect the black mold is environmental and not coming from the urinary tract.

You did not indicate what you are doing for the uric acid stones.  Typically, we recommend allopurinol to reduce uric acid levels if elevated in the blood or urine, and/or potassium citrate to alkalinize the urine.

---------- FOLLOW-UP ----------

QUESTION: Dr Leslie,

Thank you. This is not so much a follow-up question as it is a comment. Both issues have been explored on the Web and are found with Google searches such as urine settles bottom of toilet bowl and diabetes black mold toilet.  Neither has been addressed authoritatively, however.

It's comforting that you have not heard of these in your professional experience.  But both questions remain puzzling and I don't understand how the mold issue would be environmental since both toilets in my example are located in bathrooms separated only by a wall -- same pipes and water source, different urine source (mine vs wife's). In other words, the environment is for practical purposes the same.

I haven't been taking anything for the uric acid stones. Last stone passed late 2011 and I'm hoping not to develop more. Also, I'm afraid that allopurinol or potassium citrate on top of all my other drugs, and GERD, gastritis, etc, would be more than my stomach can handle or invite other harmful drug interactions.


First, urine is always going to have greater density or specific gravity than water so it will always tend to go to the bottom of the toilet to some degree.  In this light, urine sinking to the bottom of the toilet is not considered pathological.  Likewise, mold is common around toilets and does not necessarily indicate diabetes or anything else abnormal.

If you are not taking or doing anything different than previously for your uric acid stones, then it is illogical to think that you won't or couldn't make more.


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Stephen W. Leslie, MD


Questions concerning erectile dysfunction, kidney stones and prostate disorders including prostate cancer. I have a special interest in kidney stone disease prevention.


Full time practicing urologist with 30 years experience. Associate Professor of Surgery and Chief of Urology at Creighton University Medical Center. Editor in Chief of eMedicine Urology internet textbook. Author of only NIH approved book written for patients by a urologist on the subject of kidney stones "The Kidney Stones Handbook". Inventor of the "Parachute" and "Escape" kidney stone baskets and the "Calculus" stone prevention analysis computer program.

American Urological Association, Ohio State Medical Association, Sexual Medicine Society

Men's Health, Journal of Urology, Urology, Healthwatch Magazine, Emergency Medicine Monthly, eMedicine, "The Kidney Stones Handbook", and numerous articles in various newspapers. He is also the editor of the Urology Board Review by McGraw-Hill used by urologists to study for their Board Certification Examinations.

Graduate of New York Medical College with residencies completed at Metropolitan Hospital New York, Albany Medical Center and University of Wisconsin-Madison.

Awards and Honors
Thirlby Award of the American Urological Association. Rated as one the country's Best Urologists by the Independent Consumer's Research Institute

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