| Cause | Comment |
| Dehydration | Hot weather, diabetes, infection, gastroenteritis |
| Hypotension | Myocardial infarction, arrhythmia, heart failure, gastrointestinal haemorrhage, septic shock, multiple organ failure |
| Unusual posture or activity | Prolonged sitting, kneeling |
| Malignancy | Solid and haematological |
| Hyperviscosity | Polycythaemia, thrombocytosis |
| Thrombophilia | Protein C or S and antithrombin III deficiencies; activated protein C resistance; factor V Leiden; antiphospholipid syndrome |
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