Blood tests performed in the emergency and critical care setting are essential to determine the patient’s current clinical status, to enable a diagnosis to be made and to monitor stabilisation and treatment. Thus the veterinary nurse should be proficient in prompt and accurate testing, regular monitoring of the patient in the intensive care unit and early recognition of abnormal results that need to be brought to the immediate attention of the veterinarian. This article highlights commonly screened blood parameters in the emergency setting, giving normal ranges and critical values that necessitate immediate intervention to optimise patient care. Veterinary nurses with a sound knowledge of routinely screened blood parameters will be best placed to contribute to the smooth running of the intensive care unit and to provide excellent nursing care.