Urinary tract infection (UTI) may be characterized by transient albuminuria on urinary dipstick testing. The etiology of transient albuminuria in UTI is unclear but may be considered to result from glomerular or nonglomerular sources. We have theorized that nonglomerular sources are the more likely cause and could include infection-associated inflammation of the bladder mucosa with release of serum albumin into the urine and/or represent a false-positive result from red cells (RBCs), leukocytes (WBCs) and/or bacteria (BAC). To test the latter hypothesis, we mixed RBCs (fresh blood draw), WBCs (buffy coat from RBC sample), or BAC (laboratory grade E. coli for standard subcloning studies) with normal urine and performed dipstick testing for albuminuria (DTFA). All cellular fractions were prepared by washing × 3 in PBS and cell numbers determined after counting in a hemocytometer. To assess the effect of temperature, samples were examined at 24°C (room temperature) and after 1 hour at 37°C (similar to physiologic conditions). DTFA was performed using Multistix 10SG dipsticks (Bayer).
Results As shown, neither RBCs nor WBCs affected urinary dipstick albuminuria at 24°C, however, BAC gave a positive test. In contrast, at 37°C, all cellular elements gave positive DTFA. Control tubes with PBS were negative for DTFA for all conditions and temperatures. The data suggest that at 37°C, RBCs, WBCs, and BAC may result in positive DTFA in urine and that the temperature may influence the result. It is unclear from these studies if the DTFA represent a false positive (ie, interference with the dipstick) or liberation of albumin from cells.
Conclusion The transient albuminuria of UTI may result in part from RBCs, WBCs, and/or BAC giving positive DTFA. We would theorize that with therapy, the urinary concentration of the above cells is reduced, leading to a “clinical resolution” of albuminuria. Additional studies investigating combinations of cellular fractions and/or direct assays for albumin may give further clues to the etiology of this phenomenon.
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