Biological test

Indications and general principles

Performing the biological test is an absolute rule when transfusing any blood components. These include red blood cell mass, various cell suspensions, and donor plasma. The procedure is initiated immediately after connecting the administration set to the patient's venous bed, at the very beginning of the transfusion.

The main objective of this stage is to detect a potential incompatibility reaction, which may manifest as a hemolytic, allergic, or pyrogenic response. If this step is omitted and the main volume is infused immediately, the risk of life-threatening conditions increases exponentially.

Test performance algorithm

To ensure patient safety, the biological test is performed according to a strictly regulated algorithm consisting of several sequential steps. A key factor is adherence to time intervals and fluid volumes.

1. At the initial stage, the first 15–20 ml of blood is injected into the vein as a bolus.
2. Immediately after this, the transfusion is stopped for exactly 3 minutes.
3. During the resulting pause, the physician thoroughly assesses the patient's clinical status. Attention is paid to general behavior, skin color, pulse rate and character, as well as respiratory parameters.
4. The described cycle (bolus injection followed by a pause) is repeated twice more. Thus, the compatibility check is performed three times.
5. אם Если after the threefold repetition of the test no negative changes in the patient's condition are registered, proceeding to the main transfusion is permitted.

Important technical rule: in the intervals between bolus injections, during the 3-minute pause, completely shutting off the system is strictly prohibited. A slow drip infusion must be maintained. This preventive measure prevents dangerous thrombosis of the injection needle lumen.

Signs of blood incompatibility

Medical personnel must continuously monitor the patient's condition. The appearance of even one of the following symptoms during the biological test signals the development of an incompatibility reaction:

• Onset of tachycardia (marked acceleration of the pulse).
• Appearance of dyspnea and complaints of difficulty breathing.
• Sharp hyperemia (redness) of the facial skin.
• Decrease in blood pressure (BP) readings.

Upon recording the first signs of a reaction or other complications, it is necessary to immediately suspend the infusion and promptly initiate appropriate therapeutic measures.

Rate control and monitoring

Regulation of the transfusion medium flow rate is carried out using a special clamp that compresses the main tubing of the infusion set.

• Standard regimen: the transfusion is performed by drip infusion at a rate of 50–60 drops per minute.
• Bolus injection: used in case of acute necessity. For this, the clamp is opened fully.
• Pressure infusion: if emergency volume replenishment is required, a Richardson's bulb is connected to the vial, which is used to pump air inside, increasing the pressure.

Monitoring of the recipient's condition does not end at the biological test stage — careful observation is maintained throughout the entire transfusion period.

Class and exam questions

What else to study on this topic

• Mechanisms of development of hemolytic and pyrogenic reactions
• Protocol of therapeutic measures in the event of incompatibility
• Technique for the safe use of Richardson's bulb
• Specifics of performing the test when transfusing plasma compared to red blood cell mass
• Differential diagnosis of allergic reaction and incompatibility reaction

Other topics in the section "CHAPTER 6. BLOOD TRANSFUSION"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.