I have two patients who routinely have significantly lower spot protein to creatinine ratios as compared to 24-hour urine for protein.
The urine electropheresis shows non-specific proteinuria.
- The first patient is an obese young African American woman with WHO type V lupus nephritis.
- The other patient is a thin young Caucasian woman with secondary FSGS due to chronic reflux. Her most recent PCR is 1.7, and her 24-hour urine from one week prior is 4.9 g.
Any ideas? What am I missing?
No idea unfortunately.. but, I have seen this from time to time as well. It is frustrating… obviously, I am sure you are checking the total urinary creatinine quant to make sure there isn’t an over-collection.
Vegan diet?
Simon,
The urinary Cr/kg was a little generous with the Caucasian woman’s collection (something like 20 mg/kg) so there is possibly some over collection there. Additionally her CrCl exceded her MDRD by a factor of 2 (eGFR=29, CrCl=45), again consistent with an over collection. I don’t remember the mg/kg for the African American lady. I’ll look it up.
Bill,
I’m skeptical that the vegan diet would make any the midwest rustbelt and my next vegan patient will be my first vegan patient.
diurnal variation in protein excretion due to changes with orthostasis? i.e. if spot checked while lying down most of the time, then maybe low.
also maybe thin caucasian lady secretes less than a gram of Cr per day? so spot may be underestimate.
Unfortunately, I do not have an intelligent answer as to why the results should consistently be THAT far off.. But, another question comes to mind now… do you routinely get both spot U TP/Creat and 24 hr studies? I have nearly stopped all 24 hr collections for proteinuria and do so quite infrequently. But, why are you “routinely” doing both? Is that your practice in everyone with glomerular disease? Just curious… and I really like your blog by the way…
Simon
Anonymous,
That’s an interesting idea on the diurnal variation, the thing that bother’s me is that this is not a documented aspect of a spot collection. We are told to do first morning collections if possible and this should maximize the under estimation of proteinuria but generally the PCR is pretty good.
The thin Caucasian lady was well over a gram of creatinine.
Dr. Prince,
I don’t routinely get both PCR and 24 hour urines. OB at our hospital always does 24-hour urines and so they had documented the increased proteinuria so when I saw the decreased PCR I was suspicious and followed up with a 24-hour collection.