The first rapid test used to detect bacterial contamination in platelets collected for transfusion received approval from the U.S. Food and Drug Administration (FDA), as reported in the September 19 issue of The Wall Street Journal. The test, intended to be used as a supplement to other detection methods, employs test strips that can be used in the hospital setting where platelets can be tested quickly and closer to the time of transfusion. It was approved by the FDA for use with units of platelets collected by automated instrument in a procedure called apheresis. As a rapid and easy-to-use check for harmful bacteria, the test may provide an extra step for protecting critically ill patients from further complications.

Bacterial contamination of platelets is a serious concern since it is the leading cause of death from transfusion-related infections. As stated in a press release from the FDA, the risk of a patient receiving platelets contaminated with bacteria is far greater than the risk of contracting hepatitis C or HIV from a transfusion. It is an ongoing problem since units of platelets must be stored at room temperature to remain viable. This practice enables bacteria, if present, to grow more quickly and to reach numbers that may cause serious blood infections in patients who are already ill. It is thought that bacteria enter the collection bags from the donors or collection equipment. As careful as collection procedures are to avoid contamination, some bacteria may still enter the platelet collection bag, potentially causing harm to recipients. The longer platelets are stored, the greater the number of bacteria that may be present if contamination had occurred.

Since platelets are essential for blood to clot, they are often given to surgical patients or those experiencing moderate to severe bleeding episodes. They are frequently transfused into cancer patients whose level of platelets is decreased due to cancer therapy and other patients who have a low number or dysfunctional platelets.

Typically, platelets are checked for possible bacterial contamination by the blood collection facility. The platelets are sampled and cultured 24 hours after collection, and the cultures are then checked for growth of bacteria within 24 hours after that (or 48 hours after collection). If bacteria are detected at that time, the platelets are discarded. If no growth is seen on cultures, the platelets are released for transfusion. If, however, the number of bacteria was too low to detect at the time of testing, contaminated units could still be released for use. Because it takes 24 hours to confirm that no bacteria are present with a culture, it is not possible to re-test platelets just before they will be transfused using cultures.

The new rapid test detects chemicals found on the surface of bacteria. It requires the presence of at least 1,000 bacteria (in some cases, 100,000) bacteria in each milliliter (20 drops) of blood, which is less sensitive than the culture method. Because the test can be used as an extra check just before the platelets are given, when bacteria have multiplied and chances of detection are greater, the new test can be used along with culture and other currently used detection methods as an additional way to safeguard patients in need of platelets.

Sources
S1
Corbett Dooren, J. 19 Sept. 2007. Rapid Blood Test Cleared. The Wall Street Journal. Accessed October 2007. Available online: http://online.wsj.com/public/article/SB119014351543231369.html

S2
18 September 2007. US Food and Drug Administration. FDA News: FDA Clears for Marketing First Rapid Test to Screen for Bacterial Contamination in Blood Platelets. Accessed October 2007. Available online: http://www.fda.gov/bbs/topics/NEWS/2007/NEW01702.html

S3
20 September 2007. Medical News Today: Verax Biomedical Receives 510 (k) Clearance from FDA for Platelet PGD Test. Accessed October 2007. Available online: http://www.medicalnewstoday.com/articles/83039.php