If a patient with novel coronavirus pneumonia has a routine blood test, the typical patient will not have a significant elevation of white blood cells, and there may be a decrease in white blood cells. The most typical feature will be a decrease in lymphocytes, and the lower the lymphocytes, the more severe the disease is likely to be. The patient’s hematocrit tends not to change much, and the platelets also do not change much. But there may be similarities in the blood changes caused by different viral infections. There may be elevated white blood cells in bacterial infections, but bacterial infections can also cause leukopenia. So if you see a decrease in lymphocytes when a new coronavirus is present, you can see a decrease in lymphocytes, but it doesn’t allow you to make a diagnosis by blood work alone or to rule out a new coronavirus pneumonia infection. Source: Dr. Yurai