Quantitative Hemolysis Testing of Medical Devices: Standards, Methods, and Acceptance Criteria

Quantitative hemolysis testing is an essential blood-compatibility evaluation for medical devices that contact circulating blood, measuring the degree of red blood cell damage induced by device materials or their extracts. Performed in accordance with ISO 10993-4, ASTM F756, and GB/T 16886.4, the test determines the hemolysis rate through spectrophotometric quantification of released free hemoglobin, providing critical evidence for regulatory submissions, material screening, and batch quality control.

Technical Overview

Hemolysis refers to the rupture of red blood cell membranes and the subsequent release of hemoglobin into the surrounding plasma or medium. Medical devices that come into contact with blood, such as catheters, infusion sets, oxygenators, and vascular implants, may induce hemolysis through two principal mechanisms: mechanical damage caused by shear stress, turbulence, or surface roughness, and chemical damage caused by leachable substances migrating from device materials.

Quantitative hemolysis determination is a laboratory test that objectively measures the extent of red blood cell destruction caused by a medical device or biomaterial. The test is typically performed by accredited third-party laboratories following internationally recognized standards, including 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 Chinese national standard GB/T 16886.4. Sample preparation is conducted according to ISO 10993-12 and GB/T 16886.12.

The quantitative result is expressed as a hemolysis rate (hemolytic index, HI). In general, a material with a hemolysis rate of less than 5% is regarded as non-hemolytic, while values exceeding 5% indicate that the device may cause unacceptable red blood cell damage and require further evaluation or design modification.

Testing Samples

Device Categories

• External communicating devices with indirect blood contact: hypodermic needles, syringes, intravenous infusion sets, catheters, cannulae, extension tubing, and blood collection devices.
• External communicating devices with circulating blood contact: hemodialyzers, extracorporeal circuits, blood oxygenators, blood transfusion and blood storage bags, aortic balloon pumps, and cell separators.
• Implant devices with blood contact: coronary and peripheral stents, heart valves, vascular grafts, vena cava filters, closure devices, and ventricular assist components.
• Raw biomaterials: medical polymers, silicone elastomers, latex, polyurethane films, metal alloys, surface coatings, and packaging materials intended for blood-contacting applications.

Sample Preparation Requirements

Samples must represent the final product in its sterilized, clinically relevant condition. Test portions are prepared under aseptic conditions according to ISO 10993-12, using a standard ratio of material surface area or mass to extraction vehicle, for example 3 cm²/mL for flat sheets or 0.1–0.2 g/mL for irregular or absorbent materials. For complete devices, the clinical-use configuration, including flow conditions and blood-contact duration, should be considered when selecting the direct or indirect test approach.

Testing Items

The core quantitative output of the test is the hemolysis rate, supported by the following measurements:

• Hemolysis rate (hemolytic index) expressed as a percentage, calculated from sample, positive control, and negative control absorbance values.
• Free hemoglobin concentration in the test supernatant, determined by spectrophotometry at a wavelength of approximately 545 nm.
• Direct contact hemolysis, evaluating damage caused by physical interaction between the material surface and blood.
• Indirect (extraction) hemolysis, evaluating damage caused by chemical leachables released from the material.
• Supplementary plasma free hemoglobin measurement for dynamic circulation studies of blood-pumping and high-shear devices, where relevant.

Testing Methods

Direct Contact Method

In the direct contact method, the test material is incubated directly with freshly prepared, diluted anticoagulated blood, typically of rabbit or human origin. The mixture is maintained at 37 ± 1 °C for a defined incubation period, commonly three to four hours with gentle mixing. After incubation, the samples are centrifuged to remove intact cells, and the absorbance of the supernatant is measured at 545 nm using a UV-Vis spectrophotometer. This method is preferred for devices whose blood-contacting surfaces dominate the clinical exposure scenario.

Indirect Extraction Method

In the indirect method, an extract of the test material is first prepared using a physiological medium such as phosphate-buffered saline or 0.9% sodium chloride injection. Extraction is performed under one of the standard condition sets defined in ISO 10993-12, for example 37 °C for 24 hours, 50 °C for 72 hours, 70 °C for 24 hours, or 121 °C for 1 hour, selected according to the material characteristics and intended use. The extract is then mixed with diluted anticoagulated blood and incubated at 37 ± 1 °C for two to four hours before centrifugation and spectrophotometric measurement.

Controls and Reference Conditions

• Negative control: physiological saline or phosphate-buffered saline, expected to produce minimal hemolysis.
• Positive control: sterile distilled or deionized water, expected to cause complete hemolysis.
• Blank control: extraction medium without blood, used for baseline correction of the spectrophotometer.
• All tests are performed in triplicate to ensure statistical reliability, with absorbance values recorded for each replicate.

Calculation of Hemolysis Rate

The hemolysis rate is calculated using the mean absorbance values obtained from the test samples and controls: HR (%) = (A sample − A negative) / (A positive − A negative) × 100. A hemolysis rate below 5% is generally interpreted as indicating that the material or device is non-hemolytic and acceptable for blood-contacting applications, while a result of 5% or above indicates potential hemolytic activity that must be addressed through material substitution, design modification, or justification through risk assessment.

Applications

Quantitative hemolysis testing is applied at multiple stages of the medical device lifecycle:

• Regulatory submissions: providing blood-compatibility evidence for market authorization dossiers in major jurisdictions, including NMPA registration in China, FDA premarket notifications in the United States, and conformity assessment under the EU Medical Device Regulation.
• Research and development: comparative screening of candidate polymers, coatings, and surface treatments during material selection.
• Design change verification: confirming that modifications to materials, manufacturing processes, or sterilization methods do not increase hemolytic potential.
• Batch quality control: routine release testing for high-risk blood-contacting product lines.
• Incident investigation: supporting root cause analysis when hemolysis-related adverse events are reported in clinical use.

FAQ

What blood source is used for the test?

Fresh anticoagulated rabbit blood is most commonly used, typically collected with heparin or sodium citrate anticoagulation. Fresh human blood from consenting donors may also be used when clinically relevant evaluation is required. The blood must be tested promptly after collection to preserve red blood cell integrity.

What result is considered a pass?

A hemolysis rate below 5% is the widely accepted criterion for classifying a material or device as non-hemolytic. This threshold is consistent with ASTM F756 practice and is commonly applied by regulators worldwide.

When should the direct method be used instead of the indirect method?

The direct contact method is recommended when the device surface directly contacts blood under clinical conditions, such as catheters, cannulae, and blood pathway components, because it captures both mechanical and chemical effects. The indirect extraction method is suitable for evaluating leachable-related chemical hemolysis, particularly for materials with large surface areas relative to blood exposure or when direct testing is impractical.

How long does the test take?

Once samples and blood are prepared, the incubation and measurement phase typically requires one to two days. Including sample preparation, extraction time, and reporting, the complete test cycle is usually completed within one to two weeks, depending on the selected extraction conditions and laboratory scheduling.

Which standards govern the test?

The primary standards are ISO 10993-4 and GB/T 16886.4 for the selection and conduct of blood interaction tests, ASTM F756 for the assessment of hemolytic properties of materials, and ISO 10993-12 together with GB/T 16886.12 for sample preparation and reference materials.