As discussed, a CBC and peripheral smear can raise red flags that there may be leukemia in a patient, but they are not diagnostic. Extremely elevated white blood cell counts combined with serious drops in platelet levels are strongly suggestive of leukemia, but in certain leukemias, white counts can actually be abnormally low, not high. There are other clinical indications of leukemia usually present as well, e.g., excessive bruising, patient complains that they "feel terrible," etc. But that is not always true. I have seen acute leukemia that was accidentally discovered in a person who came in for a completely different reason, and they had felt just fine before their accident or injury. There are a rare few forms of leukemia where distinctive morphological structures appear in lymphocytes, mainly, but if it is some form of granulocytic leukemia, those will not be present. Only a bone marrow biopsy can confirm the diagnosis of leukemia.
Edit: Geffner Lasky, why does your link attempt to redirect me when I click on it? Where are you attempting to misdirect people to? A malicious or virus site? Looks like it because you are attempting to take people to a site in Bosnia-Herzegovina. Shame on you!