Preclinical hemolysis testing is a fundamental blood-compatibility evaluation required for medical devices that contact circulating blood, performed in accordance with ISO 10993-4, ASTM F756, and GB/T 16886.4. This article provides a technical overview of hemolysis testing principles, sample requirements, direct-contact and extraction methodologies, acceptance criteria, and typical regulatory applications. Understanding the hemolysis assay helps manufacturers complete biocompatibility documentation for device registration in China, the United States, and the European Union.
Technical Overview
Hemolysis is the rupture of red blood cells (erythrocytes) and the release of hemoglobin into the surrounding plasma. When a medical device or biomaterial contacts circulating blood, factors such as surface chemistry, material roughness, leachable substances, mechanical abrasion, and flow-induced shear stress can damage erythrocyte membranes and trigger hemolysis. Clinically, excessive free hemoglobin is associated with anemia, hemoglobinuria, renal tubular injury, and systemic inflammatory responses, which makes hemolytic potential a critical safety endpoint for blood-contacting devices.
Within the framework of ISO 10993-4 (Biological evaluation of medical devices – Part 4: Selection of tests for interactions with blood), hemolysis is classified under the hematology category, alongside thrombosis, coagulation, platelet function, and complement activation. Preclinical hemolysis testing quantifies the hemolysis rate of a device or material extract relative to negative and positive controls, typically by spectrophotometric measurement of free hemoglobin at approximately 540–545 nm, the absorption peak of oxyhemoglobin. Key reference standards include ISO 10993-4, ASTM F756 (Standard Practice for Assessment of Hemolytic Properties of Materials), and the Chinese national standard GB/T 16886.4, which is technically aligned with ISO 10993-4.
Hemolysis testing is routinely performed by accredited third-party laboratories or in-house biocompatibility facilities as part of the preclinical biological safety evaluation package required by regulatory authorities such as NMPA, FDA, and EU notified bodies under the EU MDR.
Testing Samples
Externally Communicating Blood-Contacting Devices
Devices that interface with circulating blood in use or over short durations are the primary candidates for hemolysis evaluation. Typical examples include:
- Intravenous catheters, arterial catheters, and cannulae
- Infusion sets, transfusion sets, syringes, and extension tubing
- Needles, blood lancets, and blood collection systems
- Hemodialyzers, hemoperfusion cartridges, and plasma exchange devices
- Extracorporeal circulation tubing and ECMO circuit components
- Cell-saver and autotransfusion consumables
Implantable Blood-Contacting Devices
Long-term contacting and implantable cardiovascular devices also require hemolysis assessment, either as a standalone test or as part of a broader blood-compatibility panel. Examples include:
- Vascular stents, stent grafts, and vascular prostheses
- Heart valve prostheses and cardiac occluders
- Vena cava filters and artificial vessels
- Ventricular assist devices and blood pumps
- Blood bags and blood storage containers
Raw Materials, Coatings, and Extracts
During design and development, polymer resins, elastomers, metal alloys, ceramic materials, antithrombotic or hydrophilic coatings, and process chemicals are screened for hemolytic potential using material extracts or coupon samples. Early-stage material screening reduces development risk before device-level testing is conducted.
Sample Preparation Requirements
Test samples should be representative of the final product in its finished, sterilized condition. Sample selection, surface-area-to-volume ratios, extraction vehicles, and extraction conditions follow ISO 10993-12. Sterile handling is maintained throughout testing, and test and control articles are typically evaluated in triplicate to ensure statistical reliability.
Testing Items
The core deliverable of the preclinical hemolysis study is the quantitative hemolysis rate, supported by control validation and spectrophotometric data. Typical testing items include:
- Hemolysis rate by the direct contact method, applicable to devices and materials that physically touch blood
- Hemolysis rate by the indirect contact (extraction) method, applicable to evaluation of leachable substances
- Free hemoglobin quantification in supernatant or plasma, by direct spectrophotometry or Drabkin's cyanmethemoglobin method
- Positive control (deionized water) and negative control (physiological saline or phosphate-buffered saline) validation
- Supplementary ISO 10993-4 blood-compatibility endpoints where indicated, including thrombosis, coagulation, platelet function, and complement activation testing
Testing Methods
Direct Contact Method
The direct contact method evaluates hemolysis caused by the physical interaction of the intact device or material surface with blood. Cleaned test samples are placed in sterile containers, pre-equilibrated with physiological saline at 37°C, and then incubated with freshly collected, anticoagulated, and diluted rabbit or human blood. Incubation is performed at 37°C for a duration defined by the applicable standard, commonly two to three hours, with gentle agitation to maintain uniform exposure. After incubation, samples are removed and the blood is centrifuged to separate the supernatant.
Indirect Contact (Extraction) Method
The extraction method assesses hemolysis induced by chemical leachables rather than surface contact. Test articles are extracted in physiological saline or another justified vehicle under conditions specified in ISO 10993-12, such as 37°C for 24 hours or accelerated conditions where scientifically rationalized. The resulting extract is then incubated with diluted anticoagulated blood at 37°C under controlled conditions, followed by centrifugation.
Measurement and Calculation
The absorbance of each supernatant is measured by ultraviolet-visible spectrophotometry at approximately 540–545 nm. Deionized water serves as the positive control, producing complete hemolysis, while saline or buffer serves as the negative control. 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
Results are interpreted in conjunction with control performance, replicate precision, and any observed sample-related discoloration or interference.
Dynamic Hemolysis Testing
For devices whose hemolytic risk is driven by flow dynamics, such as blood pumps, oxygenators, and extracorporeal circuits, dynamic in vitro circulation testing may be performed in accordance with device-specific standards, including ASTM F1841 for continuous-flow blood pumps. Dynamic protocols circulate blood through the device under simulated clinical flow and pressure conditions and quantify the normalized index of hemolysis over time.
Acceptance Criteria
Under widely applied criteria consistent with ASTM F756 and GB/T 16886.4, a hemolysis rate of 5% or less is generally considered non-hemolytic. Results exceeding this threshold require justification, additional risk assessment, design modification, or supplemental blood-compatibility testing. Device-specific product standards may impose stricter or additional requirements.
Applications
Preclinical hemolysis testing supports multiple regulatory and development objectives across the medical device lifecycle:
- Registration submissions to NMPA as part of the type testing and biocompatibility package for blood-contacting devices
- FDA 510(k) and PMA submissions, where ISO 10993-4-based blood-compatibility data is expected for devices contacting circulating blood
- CE marking technical documentation under the EU MDR, supporting the biological safety evaluation required by ISO 10993-1
- Material selection and surface coating optimization during research and development
- Change control evaluation after modifications to materials, suppliers, manufacturing processes, sterilization methods, or packaging
- Risk management documentation and post-market surveillance support under ISO 14971
FAQ
Which blood source is used for hemolysis testing?
Fresh anticoagulated rabbit blood is the most commonly used blood source under GB/T 16886.4 and related Chinese testing practice, while ISO 10993-4 also permits pooled or individual donor human blood collected with informed consent and appropriate ethical oversight. Sodium citrate or heparin anticoagulation is used, and the blood is diluted with physiological saline to a defined concentration before testing.
What is the acceptance criterion for the hemolysis test?
A hemolysis rate of 5% or less is the generally accepted criterion for classifying a device or material as non-hemolytic. Results above 5% do not automatically mean the device is unusable, but they require scientific justification and risk evaluation in the context of the intended clinical use and contact duration.
When is hemolysis testing required?
Hemolysis testing is expected for any device that contacts circulating blood directly or indirectly, including externally communicating devices with circulating blood contact and implantable cardiovascular devices. It is also commonly requested for infusion and transfusion consumables even when blood contact is indirect, due to the possibility of residual leachables entering the bloodstream.
Does a passing hemolysis test satisfy all ISO 10993-4 requirements?
No. ISO 10993-4 defines five blood interaction categories: thrombosis, coagulation, platelets, hematology, and complement system. Hemolysis addresses only the hematology category. Depending on device category, contact duration, and blood flow conditions, additional testing such as thrombogenicity, partial thromboplastin time, platelet activation, or complement activation may also be required.
How should samples be submitted for testing?
Samples should be provided in the final manufactured, packaged, and sterilized form, in quantities sufficient for test, control, and repeat determinations. The laboratory should receive product information, material composition, surface area or mass data, intended use, blood contact classification, and any prior extraction parameters so that sample preparation can be designed in accordance with ISO 10993-12 and the applicable test protocol.