Blood culture is indicated in all, except-

For the culture, a small sample of your blood, stool, urine or bone marrow is placed on a special medium that encourages the growth of bacteria. The culture is checked under a microscope for the presence of typhoid bacteria. A bone marrow culture often is the most sensitive test for Salmonella typhi For diagnosing subacute IE, draw 3-5 sets of blood cultures over 24 hours. This helps detect 92-98% of cases in patients who have not recently received antibiotics. In the case of acute IE, 3 sets may be drawn over 30 minutes (with separate venipunctures) to help document a continuous bacteremia Blood cultures are ordered when your doctor suspects you may have a blood infection. One such complication of a blood infection is sepsis. In sepsis, the pathogens that are causing the infection in your bloodstream interfere with your body's normal defenses and prevent your immune system from working properly. Ref Harrison20th edition pg 289