Optimising Gram stain interpretation: A comparison of four smear preparation methods for Gram staining of positively automated blood culture bottles

BackgroundAccurate and timely Gram stain interpretation of positively flagged blood culture bottles is crucial for early detection of bloodstream infections and initiation of empirical therapy. However, resin and charcoal particles in culture media may interfere with smear clarity.MethodsA prospective study was conducted on 100 positive blood culture samples. Four smear preparation techniques - conventional, water wash, blood film, and drop and rest - were applied. These were assessed for diagnostic agreement with final culture results and graded for resin/charcoal interference. Kappa (κ) statistics measured concordance.ResultsThe blood film method showed the highest agreement with culture Gram stains (63%, κ = 0.26), followed by conventional (62%, κ = 0.24), drop and rest (61%, κ = 0.22), and water wash (59%, κ = 0.18). It also had the least particle interference and the most deposit-free smears (29/100).ConclusionThe blood film method offers superior diagnostic clarity and is recommended.