Medical device hemolysis testing evaluates the degree of red blood cell damage caused by blood-contacting devices and biomaterials, forming an essential part of blood compatibility assessment under ISO 10993-4 and ASTM F756. Accredited third-party laboratories perform direct contact, indirect extract, and dynamic hemolysis assays to demonstrate that catheters, hemodialyzers, oxygenators, and other blood-path devices meet regulatory acceptance criteria before market approval. This article explains the technical principles, sample requirements, test methods, hemolysis index calculation, and typical applications of hemolysis testing for medical devices.
Technical Overview
Hemolysis is the rupture or destruction of red blood cells (erythrocytes), resulting in the release of hemoglobin into the surrounding plasma or test medium. Medical devices that contact circulating blood can induce hemolysis through several mechanisms, including the leaching of chemical substances from device materials, abrasive or rough device surfaces, mechanical shear stress generated by fluid flow, and indirect immune-mediated pathways such as complement activation.
ISO 10993-4, the international standard for the biological evaluation of medical devices with respect to blood interaction, classifies hemolysis testing within the hematology category of blood-response endpoints. The standard requires blood interaction assessment for external communicating devices that contact the blood path and for implantable devices that contact circulating blood. ASTM F756 provides a complementary methodology for assessing the hemolytic properties of materials, while GB/T 16886.4 is the corresponding Chinese national adoption of the ISO standard.
During testing, a defined volume of diluted anticoagulated blood is exposed to the test sample or to an extract prepared from the sample. After incubation at physiological temperature, the samples are centrifuged, and the absorbance of the supernatant is measured spectrophotometrically at approximately 540 nm, the wavelength at which free hemoglobin exhibits maximum absorbance. The measured absorbance is compared with negative and positive controls to calculate the hemolysis rate, providing a quantitative index of red blood cell damage attributable to the device or material.
Testing Samples
External Communicating Blood-Path Devices
Devices that indirectly communicate with the blood stream, typically for infusion, transfusion, or blood access purposes, constitute a major category of samples submitted for hemolysis testing. Representative examples include:
- Intravenous catheters, central venous catheters, and peripherally inserted central catheters
- Infusion sets, transfusion sets, extension tubing, and stopcocks
- Syringes, needles, and cannulae
- Blood collection tubes and blood bags
- Connector components and drug delivery tubing sets
Circulating Blood and Implantable Cardiovascular Devices
Devices intended for direct contact with circulating blood, whether extracorporeal or implanted, carry a heightened risk of mechanically induced hemolysis and therefore require rigorous evaluation:
- Hemodialyzers, hemofilters, and extracorporeal circuits
- Oxygenators and cardiopulmonary bypass circuits
- Extracorporeal membrane oxygenation (ECMO) system components
- Vascular stents, stent grafts, and vascular grafts
- Heart valve prostheses and ventricular assist devices
Raw Materials and Device Components
Biomaterials intended for blood-contacting applications should be screened for hemolytic potential early in the design process. Test samples may include polymeric materials, metallic alloys, surface coatings, adhesives, plasticizers, elastomers, and sterilized device components. Extracts are typically prepared in accordance with ISO 10993-12 using polar and non-polar extraction media and condition ratios appropriate to the intended clinical use of the material.
Testing Items
Hemolysis testing services for medical devices typically encompass the following analytical items:
- Hemolysis rate by direct contact method, applicable to devices or materials placed in physical contact with diluted blood
- Hemolysis rate by indirect extract method, applicable to evaluation of leachable substances released from the device
- Hemolysis index determination and material classification in accordance with ASTM F756
- Quantification of free hemoglobin concentration in plasma or test supernatant
- Supplementary hematology endpoints under ISO 10993-4, including leukocyte count, thrombosis, coagulation, platelet function, and complement activation where a broader blood compatibility profile is required
Testing Methods
Sample, Blood, and Control Preparation
Fresh anticoagulated rabbit blood or healthy human donor blood is collected using a suitable anticoagulant such as heparin, sodium citrate, or acid citrate dextrose. The whole blood is diluted with phosphate buffered saline or 0.9% sodium chloride injection to a defined ratio. A negative control, typically high-density polyethylene or another established non-hemolytic reference material, and a positive control, typically sterile distilled water or a hemolytic agent such as saponin or Triton X-100, are prepared in parallel with the test groups to validate the assay system.
Direct Contact Method
In the direct contact method, the sterilized test sample is placed in direct contact with the diluted blood. The mixture is incubated at 37 °C for a defined period, commonly two to four hours, with periodic gentle inversion to ensure uniform contact. This method is suitable for evaluating the combined effects of surface characteristics and extractable substances on red blood cell integrity.
Indirect Extract Method
In the indirect extract method, an extract of the device is first prepared according to ISO 10993-12, for example at 37 °C for 24 hours or at an accelerated condition justified for the material. The extract is then mixed with diluted blood and incubated at 37 °C. This approach isolates the hemolytic contribution of soluble leachables, making it appropriate for devices whose geometry does not permit direct immersion or where chemical toxicity is the primary concern.
Dynamic Flow Method
For devices exposed to flowing blood under clinical conditions, such as extracorporeal circuits, pumps, and heart valve prostheses, a dynamic test setup may be employed. Blood is circulated through the device or a closed loop containing the device at controlled flow rates and shear conditions, typically for several hours. This method evaluates hemolysis induced by mechanical forces, turbulence, and pressure differentials that static methods cannot reproduce.
Measurement, Calculation, and Acceptance Criteria
Following incubation, all test and control mixtures are centrifuged to sediment intact cells, and the absorbance of each supernatant is measured by ultraviolet-visible spectrophotometry at 540 nm or 545 nm. The hemolysis rate is calculated using the following relationship:
Hemolysis rate (%) = (absorbance of test sample − absorbance of negative control) / (absorbance of positive control − absorbance of negative control) × 100
A hemolysis rate of less than 5% is widely accepted by regulatory authorities as evidence that the device is non-hemolytic for biological evaluation purposes. Under the classification scheme of ASTM F756, materials with a hemolytic index of 2% or less are considered non-hemolytic, values above 2% and below 5% are considered slightly hemolytic, and values of 5% or greater are considered hemolytic. Test reports document the blood source, sample preparation conditions, incubation parameters, control results, absorbance values, and the calculated hemolysis rate.
Applications
Hemolysis testing data supports medical device development and regulatory compliance across multiple scenarios:
- Biocompatibility evaluation packages submitted for regulatory registration and market approval in major jurisdictions, in fulfillment of ISO 10993-1 and ISO 10993-4 requirements
- Design verification and design transfer for new blood-contacting devices or devices with modified materials, coatings, or manufacturing processes
- Screening of candidate biomaterials during research and development to eliminate hemolytic materials before design freeze
- Periodic quality control and change control evaluation following sterilization method changes, material supplier changes, or process revalidation
- Integration into a documented biological evaluation plan and biological risk management file consistent with ISO 10993-1 and ISO 14971
- Support for predicate comparison and substantial equivalence arguments in premarket submissions for blood-path devices
FAQ
What is medical device hemolysis testing?
It is a laboratory assay that quantifies the destruction of red blood cells caused by a medical device or its extractable materials. The test measures the free hemoglobin released from damaged erythrocytes and expresses the result as a hemolysis rate or hemolytic index relative to negative and positive controls.
Which standards govern hemolysis testing?
ISO 10993-4 defines when hemolysis testing is required and how it fits into blood compatibility evaluation, ASTM F756 describes hemolysis assessment of materials, ISO 10993-12 governs sample preparation and extraction, and GB/T 16886.4 is the corresponding Chinese national standard used for registrations in that market.
What is the acceptance criterion for hemolysis?
A hemolysis rate below 5% is generally regarded as acceptable for most blood-contacting devices, while ASTM F756 classifies materials as non-hemolytic at 2% or less, slightly hemolytic between 2% and 5%, and hemolytic at 5% or greater. Device-specific standards may impose stricter limits for certain high-flow applications.
When should the direct contact method versus the indirect extract method be used?
The direct contact method is preferred when the device physically contacts blood in clinical use, because it captures both surface-induced and leachable-induced damage. The indirect extract method is appropriate when evaluating soluble chemical hazards, when device geometry prevents immersion, or when assessing raw materials through their extracts. Many regulatory submissions include both methods to provide a complete dataset.
What blood source is used for testing?
Fresh rabbit blood is the most commonly used source due to availability and ethical considerations, while pooled or individual healthy human donor blood may be used to better reflect clinical conditions. The anticoagulant type and blood dilution ratio must be validated to ensure that the assay remains sensitive within the linear detection range of the spectrophotometric measurement.
How should samples be prepared and sterilized?
Samples must be tested in their final, sterilized form whenever possible, since sterilization can alter surface chemistry and leachable profiles. Extraction ratios, extraction media, and extraction conditions follow ISO 10993-12 unless a clinically justified alternative is documented.
Can hemolysis testing be combined with other biocompatibility tests?
Yes. Hemolysis testing is frequently performed alongside thrombogenicity, coagulation, platelet, and complement activation assays as part of a complete ISO 10993-4 blood interaction evaluation, and alongside cytotoxicity, sensitization, and irritation tests within the broader ISO 10993 biocompatibility program.
What factors commonly cause false or elevated results?
Inadequate centrifugation, hemolysis during blood collection or dilution, improper anticoagulant selection, sample particles suspended in the supernatant, and absorbance measurement outside the linear range can all distort results. Experienced accredited third-party laboratories apply validated procedures, system suitability controls, and replicate testing to ensure reliable data.