Illustrated is a spun microhematocrit tube with canine blood – the bottom red layer is packed red blood cells, above which is a small white buffy coat containing platelets and leukocytes, with supernatant plasma. In this blood from a normal dog, the plasma is colorless. To measure total solids (an estimate of total protein), a glass tube can be scored using a diamond pen or side of a glass slide. This should be done above the buffy coat, so that leukocytes, platelets or erythrocytes do not contaminate the supernatant plasma (at the location of the arrow). The tube is then broken at the line and the plasma is then transferred to the refractometer window using the unbroken (top) end of the tube.
