Background: Albuminuria is an excellent marker of cardiovascular and renal prognosis. Commercially available tests of immunodetectable albumin in the urine may not identify post-translationally modified albumin that makes it undetectable to antibodies. Also, it is unclear if albumin is degraded to smaller fragments, such as through proteolysis, in the course of acute renal injury. Methods: In twenty men with chronic kidney disease, we measured excretion rates of urine protein (pyragallol red), immundetectable urinary albumin (immunoturbidimetry), and urinary total intact albumin (HPLC) after a single dose of 100 mg intravenous iron sucrose administered over 5 minutes. Fragmentation of urinary albumin and carbonylation of urinary proteins was assessed by immunoblotting. Results: Iron infusion increased carbonylation of plasma and urinary proteins in a time dependent manner. A transient increase in urinary excretion rates of total protein, immunodetectable urinary albumin and total intact albumin was seen. Fragmentation and loss of immunoreactivity of albumin paralleled the changes in total protein excretion. Conclusions: Fragmentation, loss of immunoreactivity, and oxidation of albumin in a time dependent manner may underestimate the extent of injury with the immunoreactive microalbumin assay. Measurement of total intact albumin may better quantify acute renal injury.