What causes blood sample clumping?

From the Guidelines

Blood sample clumping is primarily caused by improper blood collection techniques, such as using a butterfly needle, which may induce contact activation and hemolysis, as well as the use of a tourniquet, which can lead to blood cell activation and hemolysis. According to the recommendations for the measurement of thrombin generation, the use of a straight needle is preferred over the butterfly needle, and the first tube of blood should be discarded to avoid contact activation 1. Other causes of blood sample clumping include:

• Using glass tubes instead of plastic tubes, which can cause contact activation by the glass material 1
• Drawing blood into a syringe and subsequently filling up the tubes, which can lead to activation of coagulation and inaccurate results 1
• Under- or overfilling of blood tubes, which can also lead to inaccurate results 1
• Presence of hemolysis or bilirubin, which can affect thrombin generation and lead to clumping 1
• Improper use of anticoagulants, such as citrate tubes at a concentration of 0.109 M, which is recommended to make comparability between laboratories easier 1. It is essential to follow proper blood collection techniques and handle samples carefully to prevent clumping and ensure accurate laboratory test results.

From the Research

Causes of Blood Sample Clumping

• Inadequate anticoagulation is a common cause of blood sample clumping, which can lead to the formation of small blood clots that can block the sample pathway of blood-gas analyzers and invalidate results 2.
• Poor mixing technique of blood with anticoagulant can also give rise to inadequate anticoagulation and the associated problems, including clumping 2.
• Preanalytical errors, such as prolonged venous stasis, collection of nonhemolyzed specimens, order of draw, and inappropriate filling and mixing of primary collection tubes, can also contribute to blood sample clumping 3.
• Storage issues, such as transportation delay, can cause blood samples to clot, leading to rejection of the sample 4.
• Platelet clumping is a common occurrence during peripheral blood hematopoietic stem cell collection, and factors such as lower white blood cell count, chemotherapy mobilization, and lower peripheral blood CD34+ cell count can predict clumping 5.
• Needle use and IV cannula are also associated with clotted samples, with odds ratios of 4.14 and 3.11, respectively 6.

Factors Influencing Blood Sample Clumping

• Heparin concentration and type can affect blood sample clumping, with high heparin concentrations and certain types of heparin increasing the risk of clumping 2.
• Blood to anticoagulant proportion and choice of anticoagulant can also influence blood sample clumping, with inappropriate proportions or choices leading to clumping 4.
• Patient-related factors, such as white blood cell count and peripheral blood CD34+ cell count, can also predict platelet clumping during peripheral blood hematopoietic stem cell collection 5.

Interventions to Reduce Blood Sample Clumping

• Quality improvement interventions, such as awareness raising and safe sampling workshops, involvement of the neonatal vascular access team, and development of a complete blood count sample collection pathway, can reduce the rate of clotted blood samples 6.
• Use of dedicated blood extraction equipment and establishment of benchmarks can also help reduce the rate of clotted specimens 6.