The amount of blood visible in the trachea at the time of examination is most commonly graded on a scale of 0 (no blood) to 4 (airways awash with blood). In some mildly-affected horses, endoscopy must be performed on multiple occasions to confirm a diagnosis of EIPH. The level of restraint required to allow endoscopy to be performed depends on the horse; a nose twitch or sedation may be required. Cytopathology Cytopathology (examination under a microscope) of either a tracheal wash or a bronchoalveolar lavage sample can determine whether EIPH has occurred. For acute hemorrhage the number of red blood cells present can be quantified using a hemocytometer. A normal lung wash sample contains fewer than 10 red blood cells/μl of fluid. In the case of EIPH, the numbers will be several magnitudes or more higher. For chronic hemorrhage the presence of high numbers of hemosiderophages, with a lot of iron inside their vesicles, indicate that hemorrhage has occurred in the lung at some time in the past. Hemosiderophages are alveolar macrophages that have ingested and digested red blood cells from previous episodes of EIPH. The end product of the digestion of the red blood cells is an iron-storage complex known as hemosiderin. Bronchoalveolar lavage Bronchoalveolar lavage (BAL) is a procedure whereby a small volume of fluid is put into the airways in order sample the cells and fluids of the alveoli and epithelium of the bronchi. BAL may be performed using a BAL tube, which allows fluid to be added to and removed from the bronchi, or may be performed during endoscopy, if the endoscope has an irrigation channel. To perform BAL, the horse is usually sedated, and local anaesthetic is usually instilled into the airways to reduce coughing. BAL is less useful when severe hemorrhage has occurred. BAL results only reflect the situation in the localized region of the lung which has been lavaged, and may not be representative of the whole lung. The fluid obtained by BAL is submitted for cytological examination. Imaging Radiography Imaging the lungs by taking a radiograph (x-ray) of the chest cannot be used to diagnose EIPH, as the lungs of affected and unaffected horses share the same characteristics. Pulmonary scintigraphy Scintigraphy of the lungs may detect moderate to severe alterations in the perfusion and possibly ventilation of the dorso-caudal lung. The use of radio-labelled red blood cells and scintigraphy to localise and