Clinical and laboratory analyses of cytospin-prepared Gram stains for recovery and diagnosis of bacteria from sterile body fluids

Abstract

The smear of a clinical specimen provides essential laboratory information that is used to make therapeutic decisions. For this study, smears were made by centrifugation in a Beckman Microfuge 11 (Beckman Instruments, Palo Alto, Calif.) and in parallel by using a Cytospin 2 apparatus (Shandon Inc., Pittsburgh, Pa.). Of 350 consecutive body fluid specimens examined, 50 (14.0%) grew bacteria. Both methods were culture and smear positive for 24 (6.9%) specimens; 18 (5.1%) specimens were cytocentrifuge smear positive, culture positive, and high-speed centrifugation (HSC) negative; 3 (0.8%) were culture negative and positive by both smear methods; and 1 (0.2%) was HSC smear positive, culture positive, and cytocentrifuge negative. Seven (2.0%) specimens were culture positive and negative by both smear methods. Clinically, cytocentrifuge preparations showed greater sensitivity for culture-positive specimens and a closer correlation with the CFU per milliliter than HSC did, resulting in a greater ability to treat patients with specific therapies. In addition, analysts needed to examine only a 6-mm-diameter area on the slide, cells and microbes were somewhat larger and more regular in appearance, and smears stained more uniformly. Because of the increased clinical and laboratory utility of the cytocentrifuge, its use is recommended in clinical microbiology laboratories for all sterile body fluid specimens.