Proteinuria - Approach

Pearls:
-Ten pounds of weight accumulates before there is detectable pitting edema.
-Types of non pitting edema include mod-severe lymphedema and myxedema.
-Anasarca is total body edema and used to be known as "dropsy."
-In sedentary patients check the sacral area of edema.

Approach to proteinuria:
-Get a UA in the office. Even if you don't have a UA, urine with protein tends to be foamy- you can ask your patient. The dipstick picks up albumin, so if it is negative, it does not rule out proteinuria. Add SSA and it will precipitate the other proteins, like light chains. Or you can order a UPEP.
-1+ protein is about 30mg/dl
-2+ protein is about 100mg/dl
-3+ protein is about 300mg/dl
-4+ protein is >2g/dl

False positives occur with recent contrast. False negatives with light chains.
-To quantify order a Spot Urine Pr/Cr = Urine Protein in mg/dl divided by Urine Creatinine in mg/dl = g/day of protein (this picks up light chains).
-With the above information you can determine if the proteinuria is glomerular, tubular, overflow or isolated. Glomerular occurs from disrupted filtration with leakage of lots of albumin. This occurs in GN and nephrotic syndrome, and is typically >4g/d. Tubular proteinuria is unlikely to be more than 1-2g/d and happens due to decreased reabsorption of already filtered proteins. Here you lose your globulins. This can be from ATN, AIN, Fanconi's. Overflow is simply that, there is over-production of freely filtered protein like myoglobin, Bence Jones, hemoglobin. Isolated includes functional proteinuria, which we seen in febrile patients or in Ellen after she runs a marathon.

(Katharine Cheung MD, 7/2/10)