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Kidney Diseases

High Urine Osmolality and High Urine Urea

03/23/2009

Question:

I am experiencing intermitant concentrated urine with decreased output (about 1000 ml despite drinking 1500 - 2000ml). I had two 24 hour urine test, both revealed high urine osmolality and high urine urea. I am also having intermitant leg edema.

Outside of these periods I am having normal urine or periods of dilute urine - but mostly its been concentrated as described above.

The diagnosis I was given was a high protein diet - but the dietician says no - plus I know my diet isn`t high in protein - perhaps too high in carbohydrates.

What else could cause high urine osmolality and high urine urea? I`ve seen protein breakdown, but what would cause that?

Thank you.

Answer:

When you say high urine urea I don't know if you are referring to the total amount in 24 hrs. or to the urine urea concentration. If the urine is concentrated (high osmolality) then the urea concentration will be high, but the total amount in 24 hrs should be about the same as when the urine is less concentrated. Your urine output won't necessarily match your intake since there will be fluid losses from your skin, your stool and your exhaled breath. Also, your input may not account for non-fluid intake since there will be fluid intake with food items like fruit and vegetables.

Even taking all this into consideration the balance between intake and output assumes you are in "steady state", meaning that there are no demands on your system to retain or unload fluid. For example if you are having edema then your body is retaining excess fluid. If your urine output exceeds your intake then your body is probably making a readjustment from excess intake or retention that preceded the day the intake and output were measured.

Another way to evaluate this is to check daily weights to see if that is stable since in a state of fluid retention your weight will increase over a short period of time(days). But your body weight should be on the average stable over the weeks unless you are gaining protein or fat stores. In other words weight fluctuations in a healthy person on a day to day basis are not usually significant. However since you have edema this needs to be explained by your doctor.

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Response by:

Thomas Zipp, MD Thomas Zipp, MD
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University