Hemolysis Testing for Medical Catheters: Standards, Methods, and Acceptance Criteria

Hemolysis testing is an essential biocompatibility evaluation for medical catheters that contact circulating blood, determining whether device materials or their extracts cause damage to red blood cells. Performed in accordance with ISO 10993-4, ASTM F756, and GB/T 16886.4, the test quantifies the hemolysis rate of catheter samples against a strict acceptance threshold, typically below 5%. This article provides a comprehensive technical overview of medical catheter hemolysis testing, covering applicable sample types, test items, methodology, calculation formulas, and regulatory applications.

Technical Overview

Hemolysis refers to the rupture of red blood cells (erythrocytes) and the subsequent release of hemoglobin into the surrounding plasma or test medium. Because many medical catheters operate in direct contact with flowing blood—often for extended periods—any material-induced damage to erythrocytes can lead to anemia, reduced oxygen-carrying capacity, thrombosis, or free hemoglobin-induced renal injury in clinical use. Hemolysis testing therefore forms a core component of the hemocompatibility evaluation required for blood-contacting medical devices.

The primary framework for this evaluation is ISO 10993-4 (Biological evaluation of medical devices — Part 4: Selection of tests for interactions with blood), which classifies blood-contacting devices by contact type (external communicating devices, implant devices) and contact duration (limited, prolonged, long-term) and identifies hemolysis as a mandatory hematological endpoint for most blood-contact categories. ASTM F756 (Standard Practice for Assessment of Hemolytic Properties of Materials) defines the laboratory methodology, while GB/T 16886.4 is the corresponding Chinese national standard adopted for domestic regulatory submissions. Additional reference may be made to GB/T 14233.2 for infusion and transfusion assemblies.

Hemocompatibility under ISO 10993-4 spans five categories: thrombosis, coagulation, platelet function, hematology, and the complement system. The hemolysis assay addresses the hematology category and is typically the first screening test performed on catheter materials, because it is rapid, sensitive, and reproducible. A material is generally regarded as non-hemolytic when the calculated hemolysis rate remains below 5% relative to positive and negative controls.

Testing Samples

Blood-Contacting Vascular Access Catheters

This category includes central venous catheters (CVC), peripherally inserted central catheters (PICC), hemodialysis and apheresis catheters, umbilical venous catheters, and sheath introducer sets. These devices maintain prolonged direct blood contact, so hemolysis evaluation is mandatory under both limited and prolonged contact categorizations.

Intravascular Diagnostic and Delivery Catheters

Coronary guide catheters, balloon dilatation catheters, microcatheters, thrombectomy catheters, and perfusion catheters fall into this group. Although contact duration is often shorter, blood contact is direct and repeated, so hemolytic assessment is required for regulatory clearance in most jurisdictions.

Sampling and Preparation Requirements

Test specimens are typically cut from the finished, sterilized catheter to represent all blood-contacting surfaces, including shaft tubing, tips, hubs, and coatings. Representative sample units are prepared under aseptic conditions, and the surface area exposed per unit volume of extraction medium is calculated according to ISO 10993-12, accounting for both inner and outer luminal surfaces of tubular sections. Both the direct contact method and the extract (indirect) method may be applied, and the finished product in its final sterilized state must be tested to capture any effects of processing, residuals, or coatings.

Testing Items

The standard testing scope for medical catheter hemolysis evaluation includes the following items:

• Hemolysis rate by the direct contact method (whole material in contact with diluted blood)
• Hemolysis rate by the extraction (indirect) method (polar saline extract exposed to diluted blood)
• Absorbance measurement of released hemoglobin in supernatant at 540–545 nm
• Positive control (deionized water) and negative control (0.9% sodium chloride injection) verification
• Optional extended hemocompatibility endpoints per ISO 10993-4: complement activation (C3a, C5a, SC5b-9), plasma free hemoglobin, thrombosis testing, coagulation assays (PT, APTT), and platelet count and activation markers

Testing Methods

Test Principle

Erythrocytes damaged by material contact or by leachable substances release hemoglobin into the surrounding medium. After incubation and centrifugation, the optical density (absorbance) of the supernatant at approximately 545 nm is proportional to the concentration of free hemoglobin. The hemolysis rate is then calculated relative to a fully hemolyzed positive control and a non-hemolytic negative control.

Direct Contact Method

Catheter segments are placed in test tubes with a defined volume of 0.9% sodium chloride injection and equilibrated at 37 °C. Freshly drawn, anticoagulated rabbit blood (anticoagulated with heparin or potassium oxalate) is diluted with saline—commonly in a ratio of approximately 8 mL blood to 10 mL saline—and a measured aliquot of diluted blood is added to each tube. Tubes are incubated at 37 °C ± 1 °C for a defined period (typically 2 to 4 hours, with gentle inversion at intervals to maintain contact). This method evaluates damage caused by surface properties, roughness, and mechanical interactions.

Extraction (Indirect) Method

Catheter samples are first extracted in physiological saline at a standardized surface-area-to-volume ratio following ISO 10993-12. Common extraction conditions include 37 °C for 24 hours for devices with short clinical contact times, with more vigorous conditions (for example, 50 °C for 72 hours or 70 °C for 24 hours) applied when justified by prolonged or long-term blood contact. The resulting extract is mixed with diluted anticoagulated rabbit blood and incubated at 37 °C, then processed in the same manner as the direct contact method. This method evaluates hemolysis induced by leachable substances, monomers, plasticizers, processing residues, and sterilant residuals.

Measurement and Calculation

Following incubation, all tubes are centrifuged (approximately 2000–2500 rpm for 5 minutes, or equivalent g-force) to sediment intact cells. The supernatant absorbance of each tube, including the positive control (deionized water, defining 100% hemolysis) and the negative control (saline, defining 0% hemolysis), is measured using a UV-Vis spectrophotometer at 545 nm. The hemolysis rate is calculated as follows:

Hemolysis rate (%) = [(A_sample − A_negative) / (A_positive − A_negative)] × 100%

where A denotes the absorbance of the test sample, negative control, and positive control respectively. Testing is performed in triplicate at minimum, and results are reported as the mean hemolysis rate with standard deviation.

Acceptance Criteria

Per ASTM F756 and GB/T 16886.4 conventions, a catheter sample is considered non-hemolytic when the mean hemolysis rate is below 5%. A result of 5% or greater classifies the material as potentially hemolytic and triggers further investigation, such as extraction optimization, material substitution, surface modification, or complementary hemocompatibility assays. Positive control hemolysis must approach 100% and negative control hemolysis must remain near zero for the test to be considered valid.

Applications

Hemolysis test reports from accredited third-party laboratories are used throughout the medical catheter product lifecycle for multiple regulatory and quality purposes:

• Market registration submissions, including NMPA registration in China, FDA 510(k) and PMA submissions in the United States, and CE technical documentation under the EU Medical Device Regulation, where ISO 10993-4 evaluation is expected
• Design verification for new catheter developments, including comparison of candidate polymers, lubricious coatings, and sterilization methods
• Change control and re-validation when raw material suppliers, manufacturing processes, or sterilization modalities are modified
• Biosecurity and quality screening during research, including biocompatibility pre-evaluation of new formulations before full ISO 10993 test series are commissioned
• Supporting documentation for biological evaluation files and risk management under ISO 14971

FAQ

What hemolysis rate is required for a medical catheter to pass?

A mean hemolysis rate below 5% is the widely accepted pass criterion under ASTM F756 and GB/T 16886.4 conventions. Values between 5% and approximately 10% warrant investigation and repeat testing, while values exceeding this range indicate a hemolytic material requiring design remediation.

Which blood source is used for the test?

Fresh rabbit blood is most commonly used because rabbit erythrocytes show sensitivity comparable to human erythrocytes and the source is standardized and readily available. Some protocols, particularly for US submissions, permit human donor blood; the choice must be justified in the test plan, and anticoagulation (heparin or oxalate) must not interfere with the assay.

When should the direct contact method versus the extraction method be used?

The direct contact method best reflects surface-mediated red cell damage and suits short-term blood-contacting devices such as angiographic catheters. The extraction method captures leachable-induced hemolysis and is essential for devices with prolonged or long-term contact, such as tunneled dialysis catheters. For comprehensive evaluation, both methods are frequently performed in parallel.

How is the extraction ratio determined for tubular catheters?

Extraction ratios follow ISO 10993-12. For tubular devices, the total wetted surface area—both inner lumen and outer wall—is calculated and extracted at a standard ratio such as 3 cm²/mL or 6 cm²/mL depending on thickness, with justification documented in the test report.

How long does hemolysis testing take?

Once samples and the biological evaluation plan are confirmed, the core assay—covering sample preparation, extraction, incubation, spectrophotometry, and calculation—is typically completed within one to two weeks. Including report issuance by accredited third-party laboratories, a full turnaround of two to four weeks is common.

Is hemolysis testing alone sufficient to demonstrate hemocompatibility?

No. Hemolysis addresses only the hematology endpoint of ISO 10993-4. Depending on contact category and duration, a complete hemocompatibility panel may also require thrombosis testing, coagulation assays, platelet function assessment, and complement activation studies. The hemolysis test is usually the initial screening step within this broader evaluation strategy.