Red blood cell hemolysis testing is a critical biocompatibility test that evaluates the potential of medical device materials and extracts to damage erythrocytes and release hemoglobin, as required by ISO 10993-4 and ASTM F756. This article provides a comprehensive technical overview of hemolysis test principles, sample preparation, direct and indirect test methods, calculation formulas, acceptance criteria, and typical applications for blood-contacting medical devices seeking regulatory approval.
Technical Overview
Hemolysis refers to the rupture of red blood cells (erythrocytes) and the release of hemoglobin into the surrounding plasma or medium. When blood-contacting medical devices damage erythrocytes beyond physiological tolerance, the consequences can include anemia, reduced oxygen-carrying capacity, hypertension, renal dysfunction, and thrombosis. Red blood cell hemolysis testing is therefore a fundamental component of the biological evaluation of medical devices performed according to ISO 10993-4 (Biological evaluation of medical devices — Part 4: Selection of tests for interactions with blood), ASTM F756 (Standard Practice for Assessment of Hemolytic Properties of Materials), and the corresponding Chinese national standard GB/T 16886.4.
During testing, the device material or a device extract is incubated with freshly drawn, anticoagulated blood under controlled conditions. The amount of hemoglobin released from damaged erythrocytes is quantified spectrophotometrically, and a hemolysis index (hemolysis rate) is calculated by comparing the absorbance of the test article against negative and positive controls. Regulatory authorities worldwide, including those reviewing submissions under the EU MDR, FDA guidance, and NMPA registration pathways, routinely require hemolysis data for devices with direct or indirect blood contact. Testing is typically performed by accredited third-party laboratories or in-house biocompatibility facilities following Good Laboratory Practice principles.
Testing Samples
Solid Device Materials
Polymeric films, sheets, tubings, metal coupons, coatings, hydrogels, and finished device components can be tested either in direct contact with blood or as extracts. For the direct contact method, samples are cut into sections with a defined surface area, cleaned to remove processing residues, and sterilized using the same method intended for the final product.
Device Extracts
For the indirect (extraction) method, test articles are extracted in a physiological medium such as phosphate-buffered saline, saline solution, or serum-containing medium according to the extraction ratios specified in ISO 10993-12. Standard ratios include 3 cm²/mL for surface-area-based samples, 0.2 g/mL for mass-based samples, and device-specific ratios for irregular geometries. Extraction is commonly performed at 37°C for 24 hours, or under accelerated conditions, depending on the intended clinical use of the device.
Finished Blood-Contacting Devices
Catheters, cannulae, infusion sets, dialyzers, oxygenators, blood bags, and extracorporeal circuit components may be tested in their final, sterilized, and ready-to-use configuration to reflect real-world blood exposure conditions.
Testing Items
The core quantitative output of the study is the hemolysis index, expressed as a percentage, which reflects the degree of red blood cell membrane damage caused by the test article. The following parameters are typically evaluated:
- Hemolysis rate (hemolysis index) of the test article compared with controls
- Absorbance of released hemoglobin measured spectrophotometrically at approximately 545 nm
- Negative control response (physiological saline or buffer, expected to produce no hemolysis)
- Positive control response (deionized water or a detergent solution, expected to produce complete hemolysis)
- Supplementary blood interaction endpoints such as plasma free hemoglobin, where applicable to dynamic blood-contacting devices under ISO 10993-4 categorization
Testing Methods
Direct Contact Method
In the direct contact method, a specified quantity of the test material is placed in direct contact with diluted fresh anticoagulated blood, typically of rabbit or human origin. The mixture is incubated at 37°C for a defined period, commonly two to four hours with gentle agitation. After incubation, the samples are centrifuged to separate intact cells, and the supernatant absorbance is measured. The direct method is most appropriate for materials intended for direct, prolonged blood contact.
Indirect Contact (Extraction) Method
In the extraction method, the test article is first extracted under conditions justified by the intended clinical use. The resulting extract is then incubated with diluted anticoagulated blood at 37°C. This approach evaluates soluble chemical leachables and is suitable for devices where the geometry prevents direct contact testing, or where the evaluation focuses on extractable substances.
Controls and Calculation
Each test run includes a negative control (physiological saline) and a positive control (deionized water or a known hemolytic agent), each incubated with blood under identical conditions. The hemolysis rate is calculated as follows:
Hemolysis Rate (%) = (Absorbance of test sample − Absorbance of negative control) / (Absorbance of positive control − Absorbance of negative control) × 100
Acceptance Criteria
- A hemolysis rate of 5% or less generally indicates the material is non-hemolytic and acceptable for blood-contacting applications.
- A hemolysis rate greater than 5% indicates hemolytic potential and requires further investigation, material redesign, or risk justification.
- Test validity requires that the positive control produces near-complete hemolysis and the negative control remains within validated limits.
Applications
Hemolysis testing supports biocompatibility evaluation, design verification, and regulatory submission across a broad range of product categories:
- Cardiovascular devices: vascular stents, grafts, heart valves, closure devices, and pacemaker leads
- Extracorporeal circulation products: hemodialyzers, hemofilters, oxygenators, ECMO circuits, and blood pumps
- Infusion and vascular access devices: intravenous catheters, infusion sets, syringes, needles, and stopcocks
- Blood collection, storage, and transfusion products: blood bags, tubing sets, and filters
- Wound dressings, hemostatic materials, and absorbable implants with potential blood exposure
- Research and development screening of novel biomaterials, surface coatings, and antithrombotic treatments
FAQ
Which standards govern red blood cell hemolysis testing for medical devices?
The primary standards are ISO 10993-4 and GB/T 16886.4 for blood interaction testing, ASTM F756 for material hemolytic properties, and ISO 10993-12 for sample preparation and extraction. Test reports referencing these standards are widely accepted in global regulatory submissions.
What blood source is used for testing?
Fresh rabbit blood is most commonly used because rabbit erythrocytes show high sensitivity and reproducibility. Human donor blood may be used where justified, and anticoagulation is achieved with heparin or citrate depending on the protocol.
How is the direct contact method chosen over the extraction method?
The direct contact method is preferred when the device surface directly contacts blood in clinical use, whereas the extraction method is selected when evaluating leachables, testing complex geometries, or when the sample cannot physically contact blood in a standardized manner.
How much sample is required for testing?
Typical requirements include 5 to 15 grams or a surface area equivalent to several hundred square centimeters per test group, plus additional material for controls and repeats, in the final sterilized condition. Exact quantities depend on the selected method and laboratory protocol.
What is considered a passing result?
A hemolysis rate of 5% or below is generally accepted as non-hemolytic. Results above this threshold require engineering review, additional blood compatibility testing, or documented risk mitigation before the device can be considered suitable for blood contact.
How long does hemolysis testing take?
Following sample preparation and extraction, the incubation and measurement phase is typically completed within one to two days, with full test reports including controls and documentation generally issued within two to four weeks.