Thrombocytopenia is a condition characterised by a decrease in platelet numbers, which is often caused by increased destruction of platelets or a decrease in production.
Thrombocytopenia can manifest in many ways – the signs can be subtle and easily missed, such as small petechiae on gums, or quite obvious signs, such as large areas of ecchymotic haemorrhage on the skin.
Ecchymotic haemorrhages are often attributed to disorders of secondary haemostasis, such as rodenticide intoxication, but it can also occur with thrombocytopenia depending on the severity and chronicity.
Other common clinical signs include:
- epistaxis
- blood in stools, urine or vomit
- pale mucus membranes
- lethargy
- weakness
Therefore, the first step to managing a patient with a severe thrombocytopenic episode that has resulted in significant blood loss is to manage shock, if present, with IV fluids, then administer a red blood cell transfusion.
Patient handling
Careful patient handling is critical as these patients can bleed easily, leading to blown veins, large bruises that contribute to the development of anaemia and significant patient discomfort. Beyond initial patient stabilisation, the next step is to determine the underlying cause.
Diagnosing thrombocytopenia is relatively straightforward with the demonstration of low platelet counts. Generally, bleeding does not occur until the platelet count drop below 40,000 thousands per cubic milliliter (k/uL). This can be determined by either a haematology machine or manually via blood smear analysis.
When assessing blood smears, the general rule is one platelet per high-powered field on the monolayer is equal to 15,000k/uL. With either method, you must assess for platelet clumping on a blood smear as this can artefactually drop platelet numbers, leading to a false diagnosis.
Causes
The diagnostic pathway should not stop there. It needs to continue to determine the underlying cause.
The most common cause of thrombocytopenia is immune-mediated destruction. This can be either a primary (diagnosis of exclusion) or secondary cause (such as Rickettsia infection, and drugs such as sulphonamides, toxins and neoplasia). Other less common causes include:
- splenomegaly, which can lead to platelet sequestration
- disseminated intravascular coagulation and acute blood loss, leading to platelet consumption
- bone marrow disease, which results in reduced platelet production
Signalment and history will refine such a diagnosis, as certain breeds are more prone to developing thrombocytopenia than others – for example, grey collies due to a defect in haematopoietic stem cells, and whippets and greyhounds, which traditionally have a lower platelet count than other breeds.
The generally diagnostic pathway continues to include haematology and biochemistry, thoracic radiographs, abdominal ultrasound and depending regional prevalence testing for infectious organisms with PCR and ELISA assays.
Next week I will cover the management principles of the thrombocytopenic patient.
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