Wright's stain, 400x

This microphotograph contains erythrocytes and leukocytes, but note the absence of platelets. When platelets are absent from a blood smear, it is important to ensure that there hasn’t been platelet clumping, which is usually found on the feathered edge of the smear. When platelets are completely absent on a smear, it is important to examine the tube containing the blood sample to ensure that clotting did not occur: rock the tube gently to notice whether there are any clots, and failing to see any, double-check by uncapping the tube and running a wooden stick through the blood that may "catch" some smaller clots. A low platelet count should always be double-checked as it may be an artefactually low count given the frequency of platelet clumping and the possibility of sample clotting due to a difficult venipuncture or an inadequate mixing of the sample with the anticoagulant.