Health Guide

Blood culture

What is this test?

This test detects and isolates aerobic and anaerobic bacteria from a culture of blood. Aerobic bacteria require oxygen to survive, while anaerobic bacteria do not require oxygen to survive. This test is used to evaluate different infections[1], such as suspected bacterial endocarditis[2][3][4], community acquired pneumonia[5][6][7][8][9], or suspected sepsis[10][11].

What are other names for this test?

  • BC - Blood culture

What are related tests?

  • Gram stain microscopy

Why do I need this test?

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

  • Cellulitis
  • Community acquired pneumonia
  • Erysipelas
  • Febrile seizure
  • Infection of the floor of the mouth
  • Infective endocarditis
  • Meningitis
  • Meningococcal blood infection
  • Sepsis syndrome

When and how often should I have this test?

When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.

Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.

The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.

This test may need to be done more than once[1].

How should I get ready for the test?

Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.

Tell the healthcare worker if you are taking any antibiotics before this test[1].

How is the test done?

When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.

A sample of blood may need to be taken from different puncture sites.

How will the test feel?

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.

What should I do after the test?

After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.

What are the risks?

Blood: During a blood draw, a hematoma (blood-filled bump under the skin) or slight bleeding from the puncture site may occur. After a blood draw, a bruise or infection may occur at the puncture site. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this test.

What are normal results for this test?

Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:

  • Adults and children: No growth

What follow up should I do after this test?

Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.

Where can I get more information?

Related Companies

  • Centers for Disease Control and Prevention (CDC) -
  • American Heart Association -
  • American Lung Association -


[1] Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.

[2] Cunha BA, Gill MV, & Lazar JM: Acute infective endocarditis.. Infect Dis Clin North Am 1996; 10:811-834.

[3] Durack DT, Luke AS, Bright DK, et al: New criteria for diagnosis of infective endocarditis: Utilization of specific echocardiographic criteria.. Am J Med 1994; 96:200-209.

[4] Tunkel AR & Kaye D: Endocarditis with negative blood cultures (editorial).. N Engl J Med 1992; 326:1215-1217.

[5] Mandell LA, Barlett JG, Dowell SF, et al: Update of practice guidelines for the management of community-acquired pneumonia in immunocompetent adults. Clin Infect Dis 2003; 37(11):1405-1433.

[6] Campbell SG, Marrie TJ, Anstey R, et al: The contribution of blood cultures to the clinical management of adult patients admitted to the hospital with community-acquired pneumonia: a prospective observational study.. Chest 2003; 123:1142-1150.

[7] ACEP (American College of Emergency Physicians): Clinical policy for the management and risk stratification of community-acquired pneumonia in adults in the emergency department.. Ann Emerg Med 2001; 38:107-113.

[8] American Thoracic Society: Guidelines for the management of adults with community acquired pneumonia: diagnosis, assessment of severity, antimicrobial therapy, and prevention.. Am J Respir Crit Care Med. 2001; 163:1730-54.

[9] Jadavji T, Law B, Lebel MH, et al: A practical guide for the diagnosis and treatment of pediatric pneumonia.. Can Med Assoc J 1997; 156:S703-S711.

[10] Dellinger RP, Carlet JM, Masur H, et al: Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock. Crit Car Med 2004; 32(3):858-873.

[11] Astiz ME & Rackow EC: Septic shock.. Lancet 1998; 351:1501-1505.

Last Updated: 7/4/2018
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