In subacute endocarditis, blood culture is used as the basis for selecting antibiotic therapy, but the positive rate is only about 75% To improve the positive rate of blood culture, attention should be paid to blood collection when the patient is cold and feverish, blood should be collected 3-5 times within 24-48 hours, at least 10mL each time, and the culture observation time should not be less than four weeks. If antibiotics have been used recently, the amount of broth in the culture bottle should be increased appropriately to reduce the concentration of antibiotics, or do to eliminate the effect of antibiotics to facilitate the growth of bacteria. If you have used penicillin, then add penicillinase to the culture medium, and add ammonia benzoate if you have used sulfonamide, etc. If necessary, you can stop using antibiotics for a week and then do the culture.