Patient is a male in late 60,s. Has nausea,decreased appetite,pale,weight

A high platelet count can occur in many different medical situations but the two basic processes involved include either an increased rate of platelet production (by the cells within the bone marrow) or by reduced removal of platelets from the blood - which is one of the functions of the spleen. Most situations that cause thrombocytosis do so by increasing platelet production, whereas reduced platelet removal occurs following surgical removal of the spleen (splenectomy).

The causes of thrombocytosis are summarised in Table 1 and described in more detail below.

Table 1: Causes of thrombocytosis

Secondary or reactive thrombocytosis

Infection (acute and chronic) Inflammatory disorders (eg Kawasaki's disease) Chronic iron deficiency Acute or chronic blood loss Tissue damage from trauma or surgery Medicines (steroid, vincristine) Splenectomy and hyposplenism Malignancy (Hodgkin's disease, solid tumours) Rebound from chemotherapy

Primary thrombocytosis

Essential thrombocytosis (non-familial) Essential thrombocytosis (familial) Chronic myeloid leukaemia Polycythaemia vera Myelofibrosis Myelodysplastic syndromes Causes of reactive (secondary) thrombocytosis The causes of reactive (secondary) thrombocytosis are described below.

Infection (acute and chronic) Infections can cause both thrombocytosis and thrombocytopenia (low platelet count). Infection in children is often accompanied by a raised platelet count, which is thought to be due to the hormones (called cytokines) that are produced as part of the body's normal defence against infection. Thrombocytosis is less common in adults who have infections. The thrombocytosis usually resolves as the infection recovers although it may take longer to settle.

Inflammatory disorders

These conditions may cause thrombocytosis by similar mechanisms to infections. Kawasaki's disease is a rare condition, mainly affecting children, in which there is widespread inflammation of the arteries. It is characteristically associated with a high platelet count that gradually resolves in the recovery phase. In adults either a high or low platelet count may accompany other features of 'autoimmune' diseases such as rheumatoid arthritis.

Acute and chronic blood loss

The response of the bone marrow to blood loss is to produce not only more red blood cells but also more platelets - this occurs in response to cytokines.

Tissue damage from trauma or surgery

The platelet count will also increase when a relatively large amount of body tissue is damaged either intentionally following surgery or with accidental damage. This is part of the natural defence mechanism to ensure adequate clot formation and prevent fatal bleeding.

Medicines

Rarely treatment with some drugs (steroid, vincristine) causes a transient increase in platelet count. These drugs are sometimes used to treat patients with a low platelet count due to idiopathic thrombocytopenic purpura .

Underactive or absent spleen

The spleen is one of the major sites for destroying platelets and if it is removed the platelet count usually increases. The increase may remain for a long time but usually it settles back into the normal range. In some conditions the spleen is present but either it does not function properly (for example in some patients with Coeliac disease) or it is shrunken (for example in sickle cell disease) and the platelet count is sometimes elevated in these conditions. In this case examination of blood cells under a microscope may reveal characteristic changes suggesting impaired function of the spleen.

What could cause platelet count to reach 2,500,000?

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