From the Guidelines
Platelet clumps on a smear are most likely indicative of a laboratory artifact, such as pseudothrombocytopenia, rather than a true medical condition. This phenomenon occurs when platelets artificially aggregate during blood collection, processing, or storage, particularly when using EDTA anticoagulant tubes, as noted in the international consensus report on the investigation and management of primary immune thrombocytopenia 1. The presence of platelet clumps can falsely lower the platelet count reported by automated analyzers.
Some key points to consider when encountering platelet clumps on a smear include:
- The possibility of pseudothrombocytopenia due to EDTA-dependent platelet agglutination, which should be excluded 1
- The need for a repeat blood draw using a different anticoagulant, such as citrate, or immediate processing of the sample to obtain accurate results
- The rare possibility that platelet clumping might represent a true clinical finding in conditions like disseminated intravascular coagulation (DIC), thrombotic thrombocytopenic purpura (TTP), or certain infections
- The importance of clinical correlation to distinguish between artifact and pathology, considering the patient's symptoms, medical history, and other laboratory findings
In cases where platelet clumping persists across multiple samples with different anticoagulants, further hematologic evaluation may be warranted to rule out underlying platelet disorders or other hematologic conditions. However, based on the current evidence, the initial assumption should be that platelet clumps are an artifact rather than a sign of an underlying medical condition, as supported by the study published in Blood 1.
From the Research
Platelet Clumps on Smear
- Platelet clumps on a smear can be an indication of pseudothrombocytopenia, which is a condition where platelets clump together in the presence of anticoagulants, such as EDTA, resulting in a falsely low platelet count 2.
- The presence of platelet clumps can also be a sign of an underlying platelet disorder, such as thrombocytopenia or thrombocytosis 3.
- Platelet clumps can be detected on a peripheral blood smear, and the sensitivity of detection can be maximized by reviewing the entire smear, including the feather edge and readable area 4.
- The definition of significant platelet clumping is still a topic of debate, but one study suggests that it can be defined as the presence of at least three platelets clumped together 5.
Detection of Platelet Clumps
- Automated hematology analyzers, such as the CellaVision DM96 and Sysmex XN, can detect platelet clumps, but their sensitivity and specificity may vary 4, 5.
- Microscopic review of the blood smear is still the gold standard for detecting platelet clumps, and it can detect clumps with a high degree of accuracy 4.
- The use of platelet-related indices, such as platelet distribution width (PDW) and mean platelet volume (MPV), can also help in detecting platelet clumps 5.