Types, Mechanisms, and Applications of Blood Collection Tube Additives

Blood collection tube additives determine the coagulation status of blood after collection, the preservation state of cellular components, and the stability of analytes, and therefore constitute an important part of pre-analytical control in blood sample handling. Different additives correspond to different sample types and testing purposes, and their selection directly affects the accuracy and comparability of test results.

 

Keywords: blood collection tube; additive; anticoagulant; clot activator; separation gel; pre-analysis; sample handling; testing application

 

1 Basic Functions of Blood Collection Tube Additives

1.1 Functional Roles in the Pre-analytical Phase

(1) Control of the coagulation process

After blood is collected, the coagulation cascade is rapidly initiated. Blood collection tube additives first determine whether the final specimen will be processed as serum, plasma, or whole blood.

(2) Stabilization of sample status

Cellular metabolism, ion transport, protein release, and enzymatic activity continue after blood collection. Additives can delay, block, or redirect these processes, thereby improving the stability of target analytes.

(3) Standardization of workflow

Blood collection tube additives affect not only sample composition, but also mixing procedures, centrifugation timing, centrifugation parameters, and storage pathways. Therefore, additive selection is directly related to the consistency of the testing workflow.

 

1.2 Major Functional Categories

(1) Anticoagulant additives

These are used to inhibit the coagulation process and obtain plasma or whole blood samples.

(2) Clot-promoting additives

These are used to accelerate coagulation and improve the efficiency of serum separation.

(3) Separation-support additives

These mainly refer to systems such as separation gels, which form a stable barrier between serum or plasma and blood cells after centrifugation.

(4) Protective and stabilizing additives

These are used to inhibit glycolysis, protect nucleic acids, maintain cellular morphology, or reduce the risk of analyte degradation.

 

2 Major Categories of Blood Collection Tube Additives

2.1 Anticoagulants

(1) Ethylenediaminetetraacetic acid salts (EDTA)

EDTA inhibits coagulation by chelating Ca2+ and is one of the most commonly used anticoagulants in hematology testing. Its advantages include relatively good preservation of cellular morphology, making it suitable for complete blood count testing, blood cell differential analysis, certain molecular assays, and some pre-analytical procedures for flow cytometry. Its limitations are that it markedly affects the measurement of calcium, magnesium, and other metal ions, and it is not suitable for coagulation testing.

(2) Heparin and its salts

Common forms include sodium heparin, lithium heparin, and ammonium heparin. Heparin inhibits coagulation by enhancing antithrombin activity and is suitable for certain biochemical assays, blood gas analysis, and emergency testing. Heparinized plasma can be obtained relatively quickly, but heparin itself may interfere with some molecular biological reactions and certain staining systems.

(3) Citrates

Sodium citrate achieves anticoagulation through reversible binding of Ca2+ and is most classically used in coagulation testing. Because its anticoagulant effect can be reversed by calcium supplementation, it is particularly suitable for coagulation analysis systems. This type of anticoagulant requires strict control of the blood-to-anticoagulant ratio, and any imbalance in this ratio directly affects the result.

(4) Oxalate/fluoride combined systems

Oxalates function as anticoagulants, whereas fluoride is mainly used to inhibit glycolysis. These combination tubes are commonly used for the detection of metabolic markers such as glucose and lactate. Their methodological value does not lie in preserving the most natural sample state, but in rapidly terminating post-collection metabolism.

 

2.2 Clot-promoting Additives

(1) Silicon dioxide-based clot-promoting particles

These accelerate clot formation by providing a contact surface for coagulation and are among the most common clot-promoting systems in routine serum tubes.

(2) Clot activators

These include certain inorganic or organic coagulation-promoting components used to shorten natural clotting time and improve sample turnaround efficiency. Their main application is serum preparation for routine clinical biochemistry and immunological testing.

 

2.3 Separation Gel

(1) Basic function

After centrifugation, the separation gel forms a stable barrier between the upper serum or plasma layer and the lower blood cell layer, thereby reducing remixing and upward displacement of cellular components.

(2) Methodological value

Its main advantages are improved workflow efficiency, better compatibility with automation, and reduced errors during subsequent sample transfer.

(3) Application boundaries

Not all test items are suitable for separation gel use. In some trace analyses, small-molecule metabolite assays, drug concentration measurements, and certain mass spectrometry applications, separation gels may introduce adsorption effects or background interference.

 

2.4 Inhibitory and Protective Additives

(1) Glycolysis inhibitors

The most typical example is sodium fluoride, which is mainly used in glucose testing systems to reduce false decreases caused by ongoing glucose consumption by blood cells after collection.

(2) Nucleic acid preservation systems

These are used in certain molecular testing blood collection tubes and emphasize leukocyte lysis control, nuclease inhibition, and nucleic acid stabilization.

(3) Cell preservation systems

These are mainly used for flow cytometric analysis, circulating tumor cell detection, special immunophenotypic analysis, or cytogenetic testing, where preservation of cellular integrity and antigen stability is critical.

Table 1 Main Categories and Functions of Common Blood Collection Tube Additives

 

Additive category	Representative type	Main function	Common sample type	Main application direction
Anticoagulant	EDTA	Chelates Ca2+ and inhibits coagulation	Whole blood, plasma	Hematology, certain molecular assays
Anticoagulant	Heparin	Inhibits the coagulation cascade	Plasma	Biochemistry, blood gas analysis, emergency testing
Anticoagulant	Sodium citrate	Reversible anticoagulation	Plasma	Coagulation testing
Anticoagulant/inhibitor	Oxalate/fluoride	Anticoagulation and glycolysis inhibition	Plasma	Glucose and lactate testing
Clot promoter	Silicon particles/clot activators	Accelerates coagulation	Serum	Routine biochemistry, immunological testing
Separation-support additive	Separation gel	Forms a stratification barrier	Serum, plasma	Automated testing, sample preservation
Protective system	Nucleic acid/cell preservative	Stabilizes target components	Specialized whole blood samples	Molecular testing, cell analysis

 

3 Mechanisms and Compatibility Characteristics of Common Additives

3.1 EDTA Systems

(1) Mechanism of action

EDTA blocks coagulation by efficiently chelating Ca2+. Because its anticoagulant effect is stable and its influence on cell morphology is relatively limited, it is most widely used in hematology.

(2) Main compatible applications

① Complete blood count and blood cell counting

② Peripheral blood cell morphological examination

③ Pre-processing for certain molecular diagnostic assays

④ Pre-analytical procedures for some flow cytometric assays

(3) Main limitations

EDTA affects Ca2+, Mg2+, and some enzyme activity-related analytes. It is not suitable for coagulation testing and should not be directly used for certain biochemical assays requiring preservation of the natural ionic state.

 

3.2 Heparin Systems

(1) Mechanism of action

Heparin inhibits activation of coagulation factors through an antithrombin-mediated mechanism and therefore represents a physiologically based anticoagulant pathway.

(2) Main compatible applications

① Emergency biochemical testing

② Blood gas analysis

③ Certain clinical chemistry assays

④ Pre-processing for some cell function experiments

(3) Main limitations

Heparin may interfere with certain PCR systems, enzymatic reactions, and staining analyses, and therefore should not be regarded as a universal anticoagulant.

 

3.3 Sodium Citrate Systems

(1) Mechanism of action

Sodium citrate temporarily interrupts coagulation by forming complexes with Ca2+, and coagulation can subsequently be restored in the testing system by calcium supplementation.

(2) Main compatible applications

① PT, APTT, TT, FIB, and other coagulation assays

② Certain erythrocyte sedimentation assays

③ Some functional coagulation analyses

(3) Main limitations

The blood-to-anticoagulant volume ratio must be strictly controlled. In samples with high hematocrit, the anticoagulant volume must also be adjusted; otherwise, systematic bias may occur.

 

3.4 Clot-promoting and Separation Gel Systems

(1) Mechanism of action

Clot-promoting additives accelerate clot formation, whereas separation gels form a stratification barrier after centrifugation. These are commonly used together in serum separation tubes.

(2) Main compatible applications

① Routine biochemical testing

② Routine immunological testing

③ Hormone and antibody assays

④ High-throughput automated sample processing

(3) Main limitations

For assays emphasizing trace analysis, small-molecule drug monitoring, or specialized research applications, it is necessary to verify in advance whether the separation gel and clot-promoting system introduce bias.

 

3.5 Glycolysis Inhibition Systems

(1) Mechanism of action

These systems slow continued glucose consumption by blood cells after collection by inhibiting the activity of glycolytic enzymes.

(2) Main compatible applications

① Glucose testing

② Lactate analysis

③ Stringent pre-analytical control for certain metabolic assays

(3) Main limitations

The purpose of these systems is not to preserve the natural state of blood, but to prioritize post-collection metabolic control; therefore, they should not be used arbitrarily as substitutes for routine biochemistry blood collection tubes.

 

4 Major Application Scenarios of Blood Collection Tube Additives

4.1 Routine Biochemical and Immunological Testing

(1) Situations in which serum systems are preferred

Most routine biochemistry assays, immunoglobulin tests, antibody tests, hormone assays, and tumor marker tests are more suitable for clot-activator tubes or serum separation tubes.

(2) Situations in which plasma systems are preferred

When rapid sample turnaround is required, prompt separation and instrument loading are needed, or when certain analytes are specifically validated in a plasma matrix, heparin tubes can improve workflow efficiency.

 

4.2 Hematology and Cell Analysis

(1) Complete blood count

EDTA remains one of the standard choices for routine hematology analysis, with emphasis on preservation of cell morphology and counting stability.

(2) Flow cytometric analysis

Depending on the target antigen and testing system, EDTA or a specific cell preservation system may be used. When delayed testing or transported samples are involved, greater attention must be paid to the effects of stabilizing additives.

 

4.3 Coagulation Function Testing

(1) Coagulation analysis

Sodium citrate is the core additive for coagulation testing. Its significance lies not merely in anticoagulation, but in providing the methodological basis for in vitro reconstitution of the coagulation cascade.

(2) Quality control requirements

Coagulation assays are highly sensitive to fill volume, mixing method, and centrifugation conditions, and therefore one anticoagulant tube cannot be substituted for another simply because both prevent clotting.

 

4.4 Molecular Testing and Specialized Sample Collection

(1) Nucleic acid testing

The collection tube should be selected according to the analytical target, using either a nucleic acid preservation tube or an anticoagulant system compatible with downstream nucleic acid extraction. Some anticoagulants may prevent clotting but are not necessarily suitable for pre-PCR or pre-sequencing handling.

(2) Cytogenetic and specialized biomarker testing

If the analytical target is circulating nucleic acids, circulating tumor cells, or specific extracellular vesicle components, the choice of blood collection tube additive directly affects preservation of the target material.

Table 2 Selection Logic of Blood Collection Tube Additives for Different Testing Directions

 

Testing direction	More commonly used additive system	Key selection consideration
Routine biochemistry	Clot activator/separation gel	Serum separation efficiency and automation compatibility
Immunological testing	Clot activator/separation gel	Stability of the serum matrix
Complete blood count	EDTA	Preservation of cellular morphology
Coagulation function	Sodium citrate	Reversible anticoagulation and ratio control
Blood gas analysis	Heparin	Rapid anticoagulation and suitability for emergency testing
Glucose/lactate	Fluoride-related systems	Inhibition of post-collection glycolysis
Molecular testing	Specific anticoagulant/protective systems	Compatibility with downstream nucleic acid workflows and stability

 

Table 3 Product Table of Blood Collection Tube Additive-Related Products

 

Product type	Catalog No.	Name	CAS No.	Grade and purity	Applicable research direction/use
EDTA anticoagulant	E1510790	Sterile EDTA.2K Anticoagulant (10×)	25102-12-9	BioReagent, sterile, 10×	Suitable for EDTA-based blood collection anticoagulant systems, mainly for hematology and pre-processing for molecular testing
EDTA anticoagulant	E1510789	EDTA.2K Anticoagulant (10×)	25102-12-9	BioReagent, 10×	Suitable for routine EDTA anticoagulant system development and formulation applications
EDTA system raw material	E100258	Ethylenediaminetetraacetic acid dipotassium salt dihydrate	25102-12-9	AR, ≥98%	Suitable as a raw material for K2EDTA anticoagulant systems
EDTA system raw material	E111797	Ethylenediaminetetraacetic acid tripotassium salt dihydrate	65501-24-8	≥99%	Suitable as a raw material for K3EDTA anticoagulant systems
Heparin system raw material	H758140	Heparin sodium salt	9041-08-1	≥99%, ≥150(units/mg)，from bovine intestinal mucosa	Suitable for heparin anticoagulant systems corresponding to plasma biochemistry and some emergency pre-analytical testing
Heparin system raw material	H101523	Heparin lithium salt	9045-22-1	≥150 USP units/mg	Suitable for lithium heparin anticoagulant systems, mainly for plasma biochemistry and rapid separation applications
Citrate system	C433300	Citrate Concentrated Solution	68-04-2	BioReagent, 4% (w/v), suitable for coagulation assays	Suitable for citrate-based anticoagulant systems for coagulation testing
Citrate system raw material	S434901	Sodium citrate dihydrate	6132-04-3	pharmaceutical grade, PharmPure™	Suitable for selection of raw materials for blood collection tube citrate systems
Oxalate/fluoride anticoagulant system	P1510793	Potassium Oxalate-Sodium Fluoride Anticoagulant	—	BioReagent	Suitable for anticoagulant and glycolysis inhibition systems used in glucose, lactate, and related assays
Oxalate/fluoride anticoagulant system	P1510794	Sterile Potassium Oxalate-Sodium Fluoride Anticoagulant	—	BioReagent, sterile	Suitable for potassium oxalate-sodium fluoride systems requiring higher sterility
Oxalate system raw material	P111570	Potassium oxalate monohydrate	6487-48-5	AR, ≥99.8%	Suitable as a raw material for oxalate anticoagulant systems
Oxalate system raw material	S299314	Sodium oxalate	62-76-0	≥99%	Suitable as a raw material for oxalate anticoagulant systems
Glycolysis inhibition system raw material	S433798	Sodium fluoride	7681-49-4	BioReagent Plus, ≥99%	Suitable for glycolysis inhibition systems in glucose and lactate testing
Clot activator	C1520196	Blood Coagulant (Water-Based)	—	BioReagent	Suitable for clot-promoting systems in serum blood collection tubes
Clot activator	C1520197	Coagulants (containing enzymes)	—	BioReagent	Suitable for clot-promoting systems requiring enhanced coagulation initiation efficiency
Clot activator	C1520198	Blood Coagulant (Alcohol-Based)	—	BioReagent	Suitable for development and application of blood collection tube clot-promoting systems
Separation gel	R1520189	Transparent Radiation-Resistant Blood Separation Gel	—	BioReagent	Suitable for serum/plasma stratification barrier systems
Separation gel	R1520190	Semi-transparent Radiation-Resistant Blood Separation Gel	—	BioReagent	Suitable for serum/plasma separation and irradiation-related application scenarios
Inner-wall treatment auxiliary material	W1520202	Water-Soluble Siliconizing Fluid	—	BioReagent	Suitable for inner-wall surface treatment and improved flow properties of blood collection tubes, and may be included as a supplementary processing material for tube manufacture

 

The selection of blood collection tube additives is, in essence, the selection of the pre-analytical pathway for the sample. Through regulation of coagulation, cellular metabolism, nucleic acid stability, and sample stratification, different additives convert the same blood specimen into analytical material suitable for different testing purposes. Understanding blood collection tube additives should therefore be based on a unified framework integrating mechanism of action, sample type, and analytical compatibility.