Utility of Slide Centrifuge Gram’s Stain Versus Quantitative Culture for Diagnosis of Urinary Tract Infection

The slide centrifuge (cytospin) Gram's-stain technique has been shown in previous studies to be a sensitive technique for detecting bacteriuria when compared to culture. The method concentrates urine sediment in a small defined area on a glass slide for Gram's staining. A positive test provides morphologic information about suspected pathogens. This study evaluated the cytospin technique using 788 urine specimens, on which routine culture was simultaneously performed, and compared both with clinical evidence for urinary tract infection. One hundred twelve of these specimens, which were cytospin positive and had a culture growing more than 100,000 CFU/mL, were assumed, by definition, to represent true urinary tract infection. Five hundred twenty-six specimens had negative cytospin and negative culture results (less than 1,000 CFU/mL) and were assumed, by definition, to rule out the diagnosis of urinary tract infection. Clinical data were evaluated for 56 cytospin-positive specimens in which culture results were less than 100,000 CFU/mL. Of these specimens, 37 were false positive (no clinical evidence of urinary tract infection), 9 had clinical evidence of urinary tract infection, and for the remaining 10, data regarding clinical status could not be interpreted. Seventy-one specimens were cytospin negative, with cultures growing more than 1,000 CFU/mL. Of these, only one patient had clinical evidence of a urinary tract infection, and his culture result was less than 10,000 CFU/mL. The predictive value of a negative cytospin test was 99.8% compared to clinical information, whereas the predictive value of a negative culture (less than 100,000 CFU/mL) was 98.4%.