In the early stages of leukemia, the number of platelets can be normal or slightly reduced. In the middle and late stages, the number of platelets can be significantly reduced, less than 10 × 10^9/L. The platelets vary in size and are deformed, including giant platelets. Factor III and coagulation dysfunction.

The number of white blood cells can reach 300 × 10^9/L when it is high, or it can be as low as (0.2~0.3) × 10^9/L (hypoproliferative leukemia). In the early stage of acute leukemia, the number of white blood cells is generally low, and in the late stage, the number of white blood cells is usually high. When the total number of white blood cells is particularly high or low, the condition is often severe, making treatment difficult and less effective. The presence of acute leukemia cells in peripheral blood is an important basis for the diagnosis of acute leukemia. Acute leukemia mainly consists of blasts and promyelocytic (blast) cells. Diagnosis is not difficult when the total number of white blood cells is high, but when the number of white blood cells is low, leukemia cells often need to be found at the tail of a concentrated smear or a blood smear. The blood picture of promyelocytic leukemia or leukemia in hypoproliferative habits often shows pancytopenia.

Routine blood tests for leukemia require fasting blood tests, most of which are biochemical tests, such as liver function, blood sugar, protein, lipids, and electrolytes potassium, sodium, chloride, etc. The reference values ??of biochemical tests are obtained from the values ??measured in fasting blood of healthy people after statistical processing. This is because the various biochemical components of the venous blood drawn before eating in the early morning of that day are relatively stable, and the various measured values ??can more truly reflect the biochemical changes of the body.

If blood is collected after eating for routine blood examination, the biochemical components in the blood (such as blood sugar, blood lipids, etc.) will temporarily change. The measured results cannot reflect the true condition of the body and cannot be compared with fasting. Reference values ??measured in blood are compared with each other, so accurate clinical judgment cannot be made. Although it is said to be on an empty stomach, there is no need to abstain from water. Drinking a small amount of water will generally not have a significant impact on the test. However, drinking large amounts of water should be avoided, as this will dilute the blood and affect the results of tests such as blood cell counts, making them lower than the true value.

Pathological changes in blood often affect tissues and organs throughout the body, and lesions of organs or tissues often cause changes in blood components. Therefore, routine blood examination is the most important and commonly used laboratory test item.