Abstract and Introduction
Abstract
We reviewed major errors in Gram stain reports from positive blood cultures to identify patterns and potential clinical impact. During a 23-month period, blood cultures were misread for 57 (0.7%) of 8,253 patients. Of 5,885 read as gram-positive cocci, 6 (0.1%) had only gram-negative organisms by culture, 3 of which were Acinetobacter species. Of 1,959 read as gram-negative bacilli, 25 (1.3%) had only gram-positive organisms by culture. Of these, 9 were Bacillus and 2 were Clostridium species. Nonrecognition of mixed Gram stains accounted for 28 errors that most often were associated with a reading of gram-positive cocci. In 4 cases, there were delays of 14 hours to 3 days in starting appropriate antibiotic treatment; 2 deaths occurred, although the erroneous Gram stain report probably was not contributory. Pathologists and laboratory personnel need to be aware of these types of misinterpretations and the potential effects on patient outcome.
Introduction
The Gram stain may be the oldest and most entrenched technique still in use in the microbiology laboratory. Because of its essential simplicity and its widespread familiarity, physicians almost never question its accuracy. Yet, no laboratory test in existence is 100% accurate, and the Gram stain is no exception owing to human interpretive error and the exigencies of the staining properties of certain bacteria. For example, it is well recognized that Bacillus species and certain other gram-positive species often stain gram-negative or gram-variable as cultures age because of cell wall changes with loss of viability.
Microbiologists are familiar with many of the problematic areas of the Gram stain, such as underdecolorization and overdecolorization and which species are likely to exhibit interpretive issues. However, we were unable to find any systematic studies in the literature of the incidence or clinical impact of misinterpretation of Gram stains. We reviewed the initial Gram stain readings for all blood cultures reported during a 23-month period, January 1, 2002, through November 30, 2003, because such errors could lead directly to the choice of an incorrect antibiotic or discontinuation of an appropriate one.