What Are Mixing Studies?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 08 August 2019
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Mixing studies are used to determine the cause of slow coagulation in a patient who is not on blood thinners or other medications that might interfere with coagulation processes. A sample of the patient’s blood can be tested in a lab to determine if the problem is a deficiency in a clotting factor, or a clotting inhibitor that makes it difficult for factors to work properly. The results can provide more information about how to proceed with diagnostic testing and eventual treatment of the issue. Medical providers may recommend mixing studies for patients experiencing recurrent unexplained bleeding, slow clotting, and related problems.

In this test, the technician separates the blood plasma and makes sure it is processed very well so it’s as pure as possible. The patient’s plasma is mixed with a sample of healthy plasma with a known concentration of clotting factors, and monitored. Technicians measure the Prothrombin Time (PT) or Partial Thromboplastin Time (PTT) or both during mixing studies, looking at how long it takes for the processed mixture to clot.

If the sample clots normally, this indicates that the patient has a clotting factor deficiency. The donor plasma provides enough clotting factors for mixing studies to help the blood clot as it would under normal conditions. Additional testing can determine precisely which blood components are involved. This information can help doctors arrive at a diagnosis and determine how to treat the patient.


A failure to clot normally means the patient’s plasma contains inhibitors that act against clotting factors to prevent coagulation. A note of caution is required when checking for inhibitors in mixing studies, as sometimes a sample will appear to clot normally, but then slow later on. This occurs when it takes time for the inhibitors to fully activate. Technicians will recheck a sample that appears to be behaving normally to confirm that it is following the coagulation cascade, indicating a problem with a clotting factor rather than an inhibitor. If the clotting behavior changes, this is the result of an inhibitor.

False test results can occur in some cases and patients may need to submit a second sample to allow a lab to recheck their findings, especially if they are unexpected. Samples can also be evaluated to look for more specific inhibitors and clotting factors, once the cause of the patient’s bleeding disorder is more apparent. Advanced testing can be more expensive, which is one reason doctors are reluctant to recommend it until it appears warranted.


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