When would you consider sputum a high-risk fluid?

When sputum contains blood, it raises concern. But people with simple bronchitis can cough up a few specks of blood. Coughing up clots of blood or persistent bloody sputum may indicate a serious problem and requires medical evaluation. People often believe that green sputum means a bacterial infection. That is not a reliable indicator. White cells that are fighting a viral infection can turn sputum green or dark yellow.