Pseudothrombocytopenia: Understanding the Unusual Platelet Phenomenon

 

Blood tests are essential tools in diagnosing various medical conditions. However, sometimes these tests can produce misleading results, such as in the case of pseudothrombocytopenia. Before we delve into pseudothrombocytopenia, let's first grasp the significance of platelets. Platelets, also known as thrombocytes, are small cell fragments in the blood produced in the bone marrow. Their primary function is to play a crucial role in haemostasis, preventing excessive bleeding when blood vessels are injured.

Pseudothrombocytopenia (Falsely low platelet count) is essentially a laboratory artifact where blood tests show low platelet counts, but the real platelet count is actually normal. It occurs when platelets clump together in the blood sample collected for analysis, leading to inaccurate platelet counts by automated cell counters. Although pseudothrombocytopenia is a benign and relatively rare condition, its accurate identification is essential to prevent unnecessary clinical interventions and misdiagnoses. 

While there are several known causes of pseudothrombocytopenia, including issues like EDTA sensitivity, giant platelets, and more, one often overlooked factor is the blood draw technique itself.

Improper Blood Sample Mixing: If the blood sample isn't mixed well timely, platelets might stick together before the test, leading to a false low count.

Ethylenediaminetetraacetic Acid (EDTA) Sensitivity: EDTA is a substance used to stop blood from clotting in test tubes. Some people are more sensitive to EDTA, which can make platelets stick together.

Cold Agglutinins: Cold agglutinins are antibodies that react at lower temperatures. When blood samples are exposed to cold conditions, these antibodies can lead to platelet aggregation.

Giant Platelets: Giant platelets, also known as macrothrombocytes, are larger than normal platelets. These oversized platelets can be mistakenly counted as other cells by automated counters, causing a false low platelet count.

Platelet Satellitism: Platelet satellitism occurs when platelets adhere to neutrophils or other white blood cells. This can create the appearance of fewer platelets in the blood sample.

Platelet Clumping Disorders: Rare platelet clumping disorders, such as Bernard-Soulier syndrome and May-Hegglin anomaly, can lead to platelet clumping and pseudothrombocytopenia.

Medications and Anticoagulants: Certain medications, like heparin, can interfere with platelet function and cause pseudothrombocytopenia.

Systemic Diseases: Underlying systemic conditions, including autoimmune diseases like systemic lupus erythematosus (SLE), can produce antibodies that lead to platelet clumping.

The Impact of Blood Draw Technique: 

• Proper Mixing: Adequate mixing of the blood sample is crucial to prevent platelet clumping. After drawing the blood into the collection tube, the tube must be gently inverted several times to ensure proper mixing with the anticoagulant (often EDTA). Inadequate mixing can lead to localized higher concentrations of EDTA, promoting platelet aggregation.
• Avoiding Hemolysis: Hemolysis, the breakdown of red blood cells, can also contribute to pseudothrombocytopenia. Hemolysis can occur when the blood draw is too forceful or when the needle isn't the appropriate size for the vein. Hemolyzed samples can cause platelets to stick together.
• Minimizing Tourniquet Time: Using a tourniquet to locate veins is common during blood draws. However, keeping the tourniquet on for an extended period can lead to changes in the blood composition and potentially cause platelets to aggregate.

Accurate diagnosis is crucial to distinguish pseudothrombocytopenia from true thrombocytopenia, a condition characterized by a low platelet count that may indicate a bleeding disorder or other serious underlying health issues. 

To confirm pseudothrombocytopenia, additional tests are typically performed:

• Platelet smear examination: A peripheral blood smear is examined under a microscope to visualize platelet clumps, giant platelets, or platelet satellitism, confirming pseudothrombocytopenia.
• Repeat testing: A repeat blood sample collected using different anticoagulants, such as citrate, may yield normal platelet counts, confirming the diagnosis.

While pseudothrombocytopenia can have various causes, including EDTA sensitivity and giant platelets, the blood draw technique is a critical factor that can either prevent or contribute to this issue. By ensuring gentle handling, adequate mixing, and minimizing tourniquet time, laboratory professionals can contribute to accurate test results, thus avoiding unnecessary concern and further medical investigations for patients. Proper blood draw technique is not just a matter of convenience; it's a fundamental aspect of providing accurate and reliable healthcare.

Dr Prashant Goyal

(Last Update: 4-Oct-2023)