Blood centrifuge separation and collection techniques and classification of blood centrifuges

Hemapheresis, or blood component separation and collection, serves two primary purposes: First, it involves separating and collecting specific blood components from healthy donors for clinical transfusion; second, when used in patients, it primarily functions as a therapeutic intervention aimed at treating disease. In such cases, hemapheresis may involve isolating specific cellular components from the patient, such as peripheral blood stem or progenitor cells, or it may be used to remove an excessive number of red blood cells from the body.

Classified by function and purpose

Generally speaking, contemporary blood cell centrifuges are designed to separate and collect various components of blood cells for different purposes. For example, depending on the specific blood cell component to be separated and collected, hemapheresis can be categorized into leukapheresis (separation and collection of white blood cells), erythrocytapheresis (separation and collection of red blood cells), plateletapheresis (separation and collection of platelets), and plasmapheresis (separation and collection of plasma), as illustrated in Figure 1-1. The aforementioned separation and collection methods can be applied both to patients and healthy donors, as well as to blood donors at blood centers.

Classification of Functions and Uses of Apheresis for Blood Component Separation

Figure 1-1: Classification of Functions and Applications for Blood Component Separation and Collection

Classified by separation technology principles

Currently available blood cell centrifuges can be classified into three major categories based on their separation technology principles: centrifugal, membrane-based, and adsorption-based. As shown in Figure 1-2, the centrifugal system is the core component of centrifugal blood cell centrifuges. According to the different blood flow modes employed by these centrifuges, they are further divided into intermittent-flow centrifuges (IFC) and continuous-flow centrifuges (CFC).

Classification of Technical Principles for Apheresis of Blood Components

Figure 1-2: Classification of Technical Principles for Blood Component Separation and Collection

1. Centrifugal blood cell centrifuge

This type of centrifuge has wide-ranging applications and is divided into the following two categories: (1) Intermittent-flow blood cell centrifuge—During operation, the IFC-type cell centrifuge, driven by a pump, draws blood from a vein through a puncture needle. After being anticoagulated, the blood flows through a separation pipeline into the centrifuge cup, where the centrifugation and separation process begins. Several collection pipelines are connected to both the centrifuge cup and collection bags, enabling the separate collection of different blood components. Under the action of centrifugal force, the plasma component is first separated, followed by the separation and collection of platelets and white blood cells. Once this process is complete, the pump reverses direction, returning the red blood cells and other blood components together back to the patient or donor. When the centrifuge cup becomes empty of blood, the entire procedure is restarted for a second round of separation and collection until the desired outcome is achieved.

The advantage of IFC centrifuges is that they require only a single venous access for blood withdrawal, centrifugation, and return of the remaining blood to the patient. However, there are also some drawbacks to their clinical use. During operation, these centrifuges involve a larger extracorporeal blood volume compared to CFC cell separators, and the exact volume of extracorporeal circulation depends on the hematocrit levels of both the patient’s and donor’s blood cells. Therefore, when using this type of cell separator clinically for blood collection from anemic patients or other therapeutic procedures, it is essential to closely monitor changes in the patient’s blood volume and to intensify nursing care.

(2) Continuous-flow blood cell centrifuge

Clinically, CFC-type blood cell separators are more commonly used. During operation, these separators simultaneously collect and return blood components. Therefore, unlike IFC-type blood cell separators, they require two venous access lines: one for drawing blood and the other for returning it. The separation and collection of blood components are carried out continuously and without interruption. Since the extracorporeal blood volume of this type of blood cell separator is smaller than that of IFC-type separators, it is generally less affected by the hematocrit of either the patient or the donor, and its blood flow remains stable. Consequently, continuous-flow blood cell separators are generally not recommended for pediatric patients.

2. Filter-membrane type blood cell centrifuge

This type of blood cell centrifuge has a narrow clinical application scope and limited use. It features a single function, primarily used for patient plasma exchange or the collection of donor plasma/platelets, and does not offer the multiple functions and applications found in centrifugal blood cell centrifuges. Its operating principle relies on the molecular sieve properties of a filter membrane to separate plasma or platelets of varying particle sizes from other blood cell components (such as red blood cells, white blood cells, and granulocytes).

3. Adsorption-type blood component centrifuge

This type of blood cell centrifuge is primarily used in clinical therapy. Clinical practice over the past decade or so has shown that this approach can indeed alleviate symptoms of certain diseases and help slow down disease progression. The underlying principle involves using specially designed immunoadsorption columns to selectively or specifically remove pathogenic substances from the plasma that are immune-related—such as antibodies or immune complexes. Removing pathogenic substances from the plasma via immunoadsorption is a new technology that has emerged in recent years. Among these, agarose columns made from staphylococcal protein A (e.g., Immunosorba) and staphylococcal protein A silica columns (e.g., Prosorba) have been approved by the U.S. FDA and regulatory authorities in several European countries for clinical use and have demonstrated promising results. Specifically removing pathogenic substances from the plasma represents an important future direction for plasma exchange and separation techniques. Using immunoadsorption or adsorbents to selectively eliminate disease-causing substances from the blood offers highly targeted and superior therapeutic benefits for the underlying disease itself. However, due to the high cost of current adsorption columns—some of which are reusable—their widespread clinical application remains limited. Nevertheless, this technology still holds great potential for further research and development.