Qualidade de amostras de escarro: análise comparativa da técnica de Gram e da contagem diferencial de células. Sample quality of sputum: comparative analysis of the Gram and diferential cell counting techniques.

objective: To estimate the level of agreement between the Gram technique and the differential cell count in the evaluation of the sputum sample quality. methodology: A prospective cross sectional study was realized. Each sample was evaluated by the Gram and cell count techniques. Samples that presented cell viability higher than 40% and less than 20% of epithelial cells, and by the Gram method, less number of epithelial and higher number of leukocytes, were classified as good quality samples. Results: Forty seven consecutive sputum samples were evaluated. Through cell differentiation count, 19(40.4%) were good quality samples. The average of absolute leukocytes was 1.69 x 10 6 cells/ml, and of epithelial cells, 55,3 x 10 6 cells/ ml. When compared the absolute number of leukocytes with the absolute number of viable cells, the Pearson correlation coefficient was 0.755. The correlations of the absolute number of viable cells and the absolute number of epithelial cells showed a negative Pearson correlation coefficient (-0.201). The quality of the sputum samples evaluated by the Gram technique demonstrated that 13 (27.7%) were good quality samples. There was poor agreement when the Gram and cell differ entiation count techniques were compared (kappa 0.35). Conclusion: The classification of sputum samples as representative or not representative of the lower respiratory tract by the Gram staining technique, with the criteria considered and used here, not agree with the results obtained with the differential cells count. The Gram staining technique is not indicated to substitute the differential cells count to evaluate the sputum quality.