Investigations

• blood tests: order cross match, U+Es, LFTs, FBC, platelets, INR, amylase:
  • haematology: haemoglobin, haematocrit - both of these may be normal until haemodilution occurs. Also, leukocytosis and thrombocythaemia are common
  • biochemistry: raised urea - due to increased protein load, LFTs - abnormal in liver disease
• endoscopy: identification of cause in >90% and permits treatment, e.g. sclerotherapy for varices, injection of adrenaline into a bleeding ulcer

If there is ongoing bleeding and the diagnosis of the site of the bleed is unknown then either a labelled red cell scan or angiography may be used. A labelled red cell scan allows detection of blood loss at rates as low as 0.1 ml/minute. Angiography cannot detect blood loss that occurs at a rate of less than 1 ml/minute. If the bleed is intermittent then both techniques may fail to localize the site of bleeding.