Fanconi syndrome

[Anicetus]

Doing pretest for pediatrics.

Came across an answer explanation that states that because the pH of the urine is 8.0, we should be thinking about hereditary Fanconi syndrome as a possibility. I can't find any sources that state fanconi syndrome makes the pH this high and in fact makes it low!! Does anyone have an explanation for why this is or is it just an errata in pretest?

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[Stoop Kid]

Sorry this is a bit late but.....

Fanconi syndrome is a tubular defect with the PCT. That means everything that the PCT reabsorbed ends up in the urine. So you're gonna see amino acids, uric acid, sodium, glucose, phosphorus in the urine. BUT most of all, you will see HCO3- in the urine (remember that the Na H transport helps reabsorb HCO3 in an indirect way along with Carbonic anhydrase). So if these HCO3 molecules end up in the urine, it will alkalize it at first. I have read that it will become acidic later on, but knowing that it will be basic is very important.

Also notice that Fanconi syndrome is the same as RTA type II because its a proximal defect. In RTA II you will see systemic acidosis because of the lack of HCO3 reabsorbtion.
ALSO, you can get syndromes similar to fanconi with nephrogenic ATN (destruction of PCT) which is done through radio contrast dyes, gentamicin and heavy metals.

Hope this helps...

 

[iBS1972]

This is a great explanation. As you are studying for Peds shelf, I am guessing that you're going to be taking Step2 and have already taken Step 1. Having said that, the question will likely ask you what is the urine pH OR give you the urine pH and have you pick the diagnosis/treatment. As such, you the urine pH will be acidic just like RTA Type 2 because the distal H-Atpase and Na/H exchange are still intact. (The of proximal tubule will be basic because of the impaired HCO3- reabsorption, but this is not as important as this is more basic science and is more of a step1 question.)
If the urine pH is basic, then it is RTA type1 (Distal RTA, due to impaired H+ excretion).