The bedside test is a blood typing procedure performed directly at the patient’s bedside without sending sample material to a laboratory. The procedure is mandatory for every physician before a blood transfusion to prevent any blood mix-ups. The test is used to directly match the blood group of the potential recipient with the nature of the container intended for use, which has already been classified and appropriately labeled in the laboratory.
What is the bedside test?
The principle of the bedside test was invented by U.S. physician and hematologist Reuben Ottenberg (1882-1959), who introduced special blood compatibility tests into practice in 1907. The test, which is still commonly used today, is performed on a small card that has two or three test fields with anti-A, anti-B and, if necessary, anti-D serum. A drop of blood is placed on each field and distributed there with a special plastic stick. In this way, the blood group in the so-called AB0 system and the rhesus factor can be reliably tested. For example, blood of blood group A with Rhesus factor positive will agglutinate (clump) on the Anti-A and Anti-D fields, while it will remain unchanged on Anti-B. On the Anti-B field, blood drops of groups B and AB will agglutinate, while blood of groups A and 0 will not change. To avoid false determinations, each individual serum is assigned to the colors commonly used in the laboratory. The test field with anti-A serum is always colored blue, while that with anti-B serum is yellow. The test result is documented in the patient’s card on a long-term basis, and the test card with the dried blood drops is destroyed after a few days for hygienic reasons. According to the relevant blood groups, the procedure is also called AB0 identity test.
Function, effect and objectives
Agglutination is the result of mixing two or more blood groups that do not match. The human body rejects what it does not know, so agglutination of foreign blood of a different blood type than the body’s own occurs. This incompatibility results from the different protein substances found in each blood group. The proteins are designated A and B and the rhesus factor. Blood group A rhesus positive (A+) therefore means that protein A is present in the blood and positive evidence for the rhesus factor is given. Rhesus negative means that this protein is not present in the specific blood group. Those who belong to blood group AB Rh-positive therefore have all three proteins. In contrast, group 0 Rh negative lacks all known protein groups in the blood. Therefore, this blood group can be used universally as a donor blood for emergencies. However, all other blood groups must match when blood is transferred from a donor to a recipient. The bedside test can be used immediately before a transfusion to determine whether this match actually exists. To exclude all risks as far as possible, both the recipient’s blood and the donor’s blood are usually examined with the bedside test in the process.
Risks, side effects, and hazards
All eligible types of transfusion blood must undergo the test, including and especially the frequently used red blood cell and granulocyte concentrates. The bedside test is also mandatory in emergencies when the patient’s life is in danger. The patient’s blood must always be drawn directly on site. Recourse to stored blood samples from the patient, regardless of the type, is categorically excluded. Even in the case of a transfusion of the patient’s own blood, the patient’s blood and the blood from the patient’s own blood bank must always be freshly subjected to the bedside test. Immediately after the test has been performed, a detailed comparison of the collected blood data of the recipient and the donor must be made. In the event of the slightest discrepancies, the upcoming transfusion process must definitely be omitted. If several transfusions are performed in succession, the bedside test must be performed again for each individual transfusion. The same applies to each change of the medical and medical staff involved. In addition, the bedside test must always be collected personally by the transfusing physician. The physician may not transfer its performance to another person. If he wishes to teach the test to an inexperienced colleague, the transfusing physician must exercise direct supervision over it.The greatest possible caution and attentiveness in connection with blood transfusions are necessary because extremely diverse possibilities for mix-ups exist and have repeatedly become a reality in the past, which no transfusing physician can oversee. The mix-ups can occur at the time of blood collection and can extend to switched units on a ward or in the operating room. In all of these cases, there can be serious consequences for blood recipients that are not infrequently life-threatening. For these reasons, the various conventional methods of bedside testing are under constant scrutiny. Uncertainties are particularly associated with the rods used to place the blood drops on the test pads of the small cards containing the serum samples. In a newly developed process, the blood is therefore applied to the respective antiserum with the aid of a syringe with a needle through an elastic cover foil. Because the foil tightly encloses the needle, it is guaranteed that neither blood nor serum can be carried away or enter foreign test fields. In addition, the small opening in the foil is closed again immediately after the puncture. After shaking, the reaction of the blood with the serum can be perceived immediately. This modern form of the bedside test only takes a maximum of ten seconds in total. This short period of time can be invaluable to the patient in emergency situations.
