Probiotics are over-the-counter dietary supplements which contain live bacteria. These bacteria are normally present in the gastrointestinal tract and may provide health benefits when added to a regular diet. Common reasons for taking probiotic supplements include repopulating the gut with lactobacilli after taking antibiotics and aiding in the treatment of inflammatory bowel disease, lactose intolerance, and gastrointestinal infections.
The gut of neonates is sterile and becomes colonized with bacteria during the first few months of life. Many of these bacteria possess terminal sugar structures on their membrane components that are chemically similar to A and B blood group substances present on red cells. Antibodies to A and B blood group substances are not present at birth. Early in life, infants lacking A or B antigens on their red cells recognize the corresponding antigens on bacteria and form antibodies against bacterial sugars that cross react with the corresponding red cell antigen. These antibodies are known as anti-A and anti-B isoagglutinins. They do not cause disease, but are important in the transfusion of compatible blood units.
Prior studies have suggested that probiotics consumed in large doses may provoke the formation of high titer isoagglutinins. This has relevance for transfusion of platelet components, in that, since ABO-matching of platelets is not necessary, minor ABO-incompatibility between donor and recipient is present in 10-20% of plateletpheresis components transfused nationwide. Plateletpheresis components derived from donors taking probiotics might contain high titer isoagglutinins, which could cause hemolytic reactions in group A and B recipients.
The objectives of this study are (1) to determine whether taking oral probiotic supplements increases anti-A and anti-B isoagglutinins in healthy subjects, (2) to study the frequency of these effects and determine whether there is a dose-response relationship with probiotics and isoagglutinin titers.
Study subjects will be asked to take a probiotic supplement at a dose of 1-3 caplets per day for 18 weeks. Blood samples will be drawn every 2 weeks during that time. Depending on individual results, continued blood testing may be done every 3 months for a year, then every 6-12 months for up to 5 years. A group of control subjects will be followed in a similar manner, but will not take probiotic supplements. The outcome measure is the percent of probiotic ingestors versus controls who experience a four-fold or greater rise in isoagglutinin titer in association with a final titer of at least 128.
