Blood Tests for Fungal Infections

How is blood testing for Fungus and infections performed?

Blood cultures are done to detect and identify bacteria and yeasts (a type of fungus) in the blood. Typically, blood is usually drawn into two types of containers each used to detect different types of bacteria and or fungus. If your blood culture is positive, the specific bacteria or fungus causing the infection will be identified and antibiotic or antifungal susceptibility testing will be done to tell your doctor which remedy would be best. If yeasts or fungus organisms are causing the infection, an appropriate remedy will be used. It is common for advanced toenail or nail fungus to spread to the bloodstream.

Infections of the bloodstream are caused most commonly by bacteria (bacteremia), but can also be caused by a fungus (fungemia) or a virus (viremia). If your immune system and white blood cells cannot contain an infection at its source, for example in the bladder for a urinary tract infection, the infection may spread to your bloodstream and be carried throughout your body. Similarly, anyone with a compromised immune system has a higher incidence of bloodstream infections.

How is the blood sample taken?

Multiple samples are collected and different veins are used. This is for two reasons: 1) when multiple samples are done, you have a better chance of detecting the infection; and 2) sometimes, despite disinfection of the skin where the blood is collected, you could have some organisms on the skin at the site of the needle puncture, which will result in a positive blood culture that is not clinically significant (a false positive). With multiple samples, you have a better chance of ruling out a false positive and deciding what is a true infection.

Blood is obtained by inserting a needle into a vein in your arm. The drawing site will be properly cleaned, usually with an isopropyl alcohol solution, followed by an iodine solution that is put on in a circular pattern and then allowed to dry. The phlebotomist will then draw about 20 mls of blood and put it into two culture bottles containing broth to grow aerobic and anaerobic microorganisms. These two bottles constitute one blood culture set. A second set of blood cultures should be collected from a different venipuncture site 5 to 60 min later, depending on the procedure being followed. Any additional samples may be taken at a later date to confirm a negative finding or to asses the response.