Urinary biochemistry and microscopy in septic acute renal failure: a systematic review

Biochemistry and microscopy of urine are widely published diagnostic activities in patients with acute renal failure (ARF). However, their scientific basis in patients with septic ARF has not been assessed systematically.

We performed a systematic review of MEDLINE, EMBASE, CINHAL, and PubMed databases and bibliographies of retrieved articles for all studies describing urinary biochemistry, indices, and microscopy in patients with septic ARF.

We identified 27 articles (1,432 patients). Because of substantial heterogeneity, no formal quantitative analysis could be performed. Urinary biochemistry or derived indices were reported in 24 articles (89%), and microscopy, in 7 articles (26%). The majority were small single-center reports and had serious limitations. For example, only 52% of patients were septic, only 54% of patients had ARF, many studies failed to include a control group, time from diagnosis of sepsis or ARF to measure of urinary tests was variable, and there were numerous potential confounders. Urinary sodium, fractional excretion of sodium, urinary-plasma creatinine ratio, urinary osmolality, urinary-plasma osmolality ratio, and serum urea-creatinine ratio showed variable and inconsistent results. Low-molecular-weight proteinuria was described in only 22% of articles. A few reports of urinary microscopy described muddy brown/epithelial cell casts and renal tubular cells in patients with septic ARF, whereas others described normal urinary sediment.

The scientific basis for the use of urinary biochemistry, indices, and microscopy in patients with septic ARF is weak. More research is required to describe their accuracy, pattern, and time course in patients with septic ARF.