Hemolysis Performance Evaluation of Medical Devices: Standards, Methods, and Acceptance Criteria

Hemolysis performance evaluation is a core biocompatibility test for medical devices that contact circulating blood, demonstrating that device materials, surfaces, and fluid pathways do not cause excessive red blood cell destruction. Performed in accordance with ASTM F756, ISO 10993-4, and GB/T 16886.4, the test quantifies the hemolysis rate and supports regulatory submissions in markets worldwide. This article explains the technical principles, sample requirements, test items, laboratory methods, acceptance criteria, and typical applications of hemolysis performance evaluation for medical devices.

Technical Overview

Hemolysis is the rupture of red blood cell membranes and the release of hemoglobin into the surrounding plasma. Blood-contacting medical devices can induce hemolysis through mechanical shear stress, turbulent flow, sharp geometric edges, rough surface textures, or cytotoxic substances leached from polymers, plasticizers, colorants, and processing residues. Clinically, excessive hemolysis reduces oxygen-carrying capacity and may lead to free hemoglobin-mediated renal tubular injury, vasoconstriction, and systemic inflammatory responses. For these reasons, hemolysis testing is a mandatory element of the biological evaluation of blood-contacting devices and is categorized under the hematology section of blood-interaction testing described in ISO 10993-4 and its Chinese counterpart GB/T 16886.4.

The principal laboratory practice for assessing the hemolytic properties of materials is ASTM F756, which defines test procedures, control requirements, and the calculation of the hemolysis index. In this test, anticoagulated blood is exposed to a device, a device extract, or a material specimen; the released hemoglobin is measured spectrophotometrically; and the result is compared against a fully hemolyzed positive control and a non-hemolytic negative control. The outcome is expressed as a percentage hemolysis rate. In most regulatory frameworks, a hemolysis rate of 5% or less is interpreted as indicating that the device or material is practically non-hemolytic, while results above 5% require scientific justification, risk assessment, or design modification.

Because hemolysis evaluation is rapid, sensitive, and cost-effective relative to animal studies, it is routinely performed during material screening, design verification, change control, sterilization validation, and periodic quality surveillance, most commonly by accredited third-party laboratories equipped with biosafety facilities and validated spectrophotometric instrumentation.

Testing Samples

Finished Blood-Contacting Devices

The preferred test article is the sterile finished device, or the blood-contacting portion of it, in its final manufactured, cleaned, and sterilized condition. Molding parameters, additives, sterilization residuals, coatings, and surface treatments all influence hemolytic potential, so testing the final product provides the most representative evidence. Typical examples include catheter shafts and tips, cannulae, tubing sets, filter membranes, pump chambers, and oxygenator components.

Material Specimens and Coupons

During research and early material screening, representative coupons of candidate materials are tested instead of the finished device. Sample preparation follows ISO 10993-12, with commonly applied ratios of 3 cm² of total surface area per milliliter of extraction vehicle for thin sheets, 6 cm²/mL when both surfaces are exposed, and 0.1 to 0.2 g of material per milliliter for irregularly shaped solids.

Extracts and Test Solutions

For the indirect method, aqueous extracts are prepared using 0.9% sodium chloride injection or serum-free cell culture medium under justified conditions such as 37 °C for 24 hours, 50 °C for 72 hours, or 70 °C for 24 hours, selected to simulate or exaggerate the intended clinical exposure. The extraction vehicle itself serves as the negative control, and a parallel extract of a known non-hemolytic reference material may be included to confirm system suitability.

Blood Specimens

Fresh rabbit blood collected with minimal trauma and anticoagulated with sodium citrate or acid-citrate-dextrose (ACD) is the most widely used test system and is explicitly contemplated in ASTM F756. Fresh human donor blood obtained with appropriate ethical consent is equally acceptable. The blood must be free of baseline hemolysis and processed promptly, as erythrocyte fragility increases with storage time.

Testing Items

Depending on the device type, contact duration, and applicable standard, the following parameters are determined:

• Hemolysis rate (hemolysis index), expressed as a percentage relative to positive and negative controls
• Plasma free hemoglobin concentration in mg/dL or g/L, measured by direct spectrophotometry or the cyanmethemoglobin (Drabkin's) method at approximately 540 to 545 nm
• Absorbance values of test, positive control, and negative control supernatants at 545 nm
• Normalized index of hemolysis (NIH, g/100 L) and modified index of hemolysis (MIH) for dynamic blood-handling devices such as blood pumps and oxygenators, calculated from the rise in plasma free hemoglobin relative to the volume of blood processed, per ASTM F1841 and ISO 7199
• Supporting indicators such as lactate dehydrogenase (LDH), hematocrit, and erythrocyte counts, used to corroborate the extent of red blood cell damage

Testing Methods

Indirect Contact (Extraction) Method

The extract is mixed with fresh anticoagulated blood that has been diluted with saline or phosphate-buffered saline to a standardized hemoglobin concentration of approximately 10 mg/mL, as described in ASTM F756. Aliquots of the diluted blood, commonly 0.2 mL added to 10 mL of each solution, are dispensed into the test extract, the positive control (deionized water or a detergent solution producing complete hemolysis), and the negative control (extraction vehicle). The tubes are incubated at 37 ± 1 °C for a defined period, typically 3 hours, with periodic gentle inversion to maintain uniform exposure. After incubation, the samples are centrifuged, for example at 800 × g for 5 minutes, to sediment intact erythrocytes, and the absorbance of each supernatant is measured at 545 nm. The hemolysis rate is calculated as (absorbance of test sample − absorbance of negative control) / (absorbance of positive control − absorbance of negative control) × 100%.

Direct Contact Method

In the direct contact method, the material coupon or device section is placed in intimate contact with the diluted blood at a documented mass-to-volume or surface-area-to-volume ratio justified according to ISO 10993-12. Incubation is performed at 37 °C, generally with gentle agitation, after which the blood is centrifuged and analyzed identically to the indirect method. This approach better reflects surface-mediated erythrocyte damage and is preferred when leachable-driven hemolysis is not the only mechanism of concern, such as for devices with large material surface areas or textured blood-contacting surfaces.

Dynamic Recirculation Method for Active Devices

For devices that actively pump, oxygenate, or otherwise process blood, a static test cannot reproduce the shear environment of clinical use. In the dynamic method, the device is connected to a closed mock circulation loop primed with fresh blood, which is circulated at clinically relevant flow rates, pressures, and temperatures for several hours, with serial blood samples drawn at defined intervals. The time-dependent increase in plasma free hemoglobin is used to calculate the NIH or MIH. Reference standards include ASTM F1841 for continuous-flow blood pumps, ISO 7199 for extracorporeal blood gas exchangers, and the blood-contact categorization guidance of ISO 10993-4, with blood selection often guided by ASTM F1830.

Controls, Validity, and Acceptance Criteria

Each test run must satisfy predefined validity criteria: the positive control must achieve essentially complete hemolysis, the negative control absorbance must be low and reproducible, and replicate variability must remain within established limits, typically with triplicate tubes per group. Because results are influenced by donor-to-donor biological variability, testing with blood from multiple donors or independent preparations is recommended. A hemolysis rate of 5% or less is conventionally accepted as non-hemolytic; values above 5% trigger investigation into the causative material, surface, or flow geometry and require either design remediation or a documented toxicological rationale.

Applications

Hemolysis performance evaluation is applied throughout the product life cycle of blood-contacting devices, from early material comparison to post-market change verification:

• Short-term external communicating devices: intravascular catheters, guidewires, introducer sheaths, angiographic and electrophysiology catheters, infusion sets, transfusion sets, needles, and syringes
• Long-term communicating and implantable devices: coronary and peripheral stents, stent-grafts, vascular grafts, prosthetic heart valves, septal occluders, and ventricular assist devices
• Extracorporeal circulation systems: membrane oxygenators for ECMO, cardiopulmonary bypass circuits, hemodialyzers, hemoperfusion cartridges, apheresis and cell-salvage systems, blood warmers, and in-line blood filters
• Blood collection and storage products: blood collection bags, tubing, and storage containers
• Materials and combination products: polymer compounds, hydrophilic lubricious and antithrombotic surface coatings, drug-eluting devices, and nanoparticle-based delivery systems
• Regulatory and quality support: design verification data for 510(k) and PMA submissions, technical documentation under the EU MDR, NMPA registration dossiers, biological evaluation reports under ISO 10993 and GB/T 16886, supplier and process change assessments, sterilization validations, and periodic batch screening

FAQ

What hemolysis rate is considered acceptable for a medical device?

A hemolysis rate of 5% or less is generally regarded as indicating a non-hemolytic device or material. Rates above 5% are typically classified as hemolytic and require investigation, toxicological justification, or design and material modification before the device can be considered biocompatible for blood contact.

Should the direct contact method or the extraction method be selected?

The extraction method is appropriate when hemolysis is expected to arise primarily from leachable substances and is the most widely applied approach for general screening and for catheter and tubing products. The direct contact method better captures surface-mediated red blood cell damage and suits devices with large blood-contacting surfaces. For pumps, oxygenators, and other flow-driven devices, a dynamic recirculation test is the most clinically relevant. Selection should follow the intended use and blood-contact categorization defined in ISO 10993-4.

Which blood and anticoagulant are used in the test?

Fresh rabbit blood anticoagulated with sodium citrate or ACD is the most common choice and is contemplated in ASTM F756. Fresh human donor blood obtained with informed consent is equally acceptable. Citrate-based anticoagulants are preferred for static assays, whereas heparinized blood is frequently used in dynamic circulation loops where longer test durations are required.

Why is absorbance measured at approximately 545 nm?

The absorbance maximum of oxyhemoglobin and of the stable cyanmethemoglobin complex lies near 540 to 545 nm. Reading the centrifuged plasma supernatant at this wavelength therefore provides a direct and sensitive measurement of free hemoglobin. Drabkin's reagent converts all hemoglobin derivatives into the cyanmethemoglobin form, which improves accuracy when hemoglobin degradation products are present.

Is hemolysis testing required for regulatory submission?

Yes. For any device with direct or indirect blood contact, hemolysis data are an expected element of the biological evaluation documentation under ISO 10993-4 and GB/T 16886.4, and are routinely requested in submissions such as FDA 510(k) and PMA applications, EU MDR technical files, and NMPA registration dossiers. Reports issued by accredited third-party laboratories are widely accepted in support of these submissions.

What information is included in a hemolysis test report?

A complete report identifies the test article and its condition, describes sample preparation and extraction parameters, documents the blood source and anticoagulant, states incubation and centrifugation conditions, presents raw absorbance data for all groups, shows the calculated hemolysis rate with control validity checks, and provides a conclusion against the 5% acceptance threshold together with any protocol deviations.