Importance of Peripheral Smear in Blood Cancer (Acute Leukemia)
Peripheral blood smear is a basic test still used despite other current molecular techniques available to diagnose blood disorders. A request for a blood smear is usually called for by the clinician in case of a patient presenting with fever to establish any parasites (malaria) or when clinical features suggest possible blood disorders. A laboratory can also alert the clinician to request for a blood smear in case the CBC is abnormal such as unexplained leukocytosis(increased number of white blood cells), lymphocytosis(specialized white blood cells), or monocytosis or when an automated instrument suggests the presence of abnormal shaped (blast) cells.
The peripheral blood smear is of great importance as it exposes the morphology of peripheral blood cells based on the fact that white blood cell count is increased with immature blast (lymphoblast or myeloblast) cells and decreased neutrophils and platelets.
The presence of the excess number of blast cells in peripheral blood is a significant symptom of leukemia. The two main types of acute leukemias are acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML).
“Acute” means that the leukemia can progress quickly, and if not treated, is likely to be fatal within a few months. The number of normal white cells in the peripheral smear varies between 3000 -11,000 per cubic millimeter. In acute leukemia-blood cancer the number of cells are >20,000/cmm and if the number of cells is >50,000/ cmm a very high index of suspicion for blood cancer needs to be entertained. A blood count of 11,000-20,000/cmm can be seen in acute infections also.
The incidence of blood cancers is less than 5% of all cancers. The most common acute blood cancer is the Acute Lymphatic Leukemia (ALL) in approximately 70% of the leukemia cases each year. ALL is the most common type of cancer and leukemia in children. Early diagnosis of the disease is fundamental for the recovery of patients especially in the case of children. The doubling time for white blood cells is shortened to <24 hours in acute leukemia, hence an early diagnosis and implementation of comprehensive treatment becomes urgent, almost an emergency.
In ALL, there is a dense and abnormal and uncontrollable proliferation of lymphoid precursors called lymphoblasts (immature lymphocytes not normally found) in the bone marrow with arrested maturation. The smear will not have enough red blood cells or platelets. The peripheral blood smear will confirm the findings of the Complete Blood Counts.
Acute myeloid leukemia (AML) is a malignant disease of the bone marrow with symptoms resulting from bone marrow failure and is more common in adults than in children.
Unlike ALL that develops from immature forms of lymphocytes, a type of white blood cell, AML is diagnosed in other blood cell types found in the bone marrow. The symptoms result from organ infiltration with leukemic cells, or both and workup includes blood tests, bone marrow aspiration and biopsy.
The confirmatory test for a blood cancer is bone marrow aspiration and biopsy that needs to be carried under a trained doctor who understands these diseases and is called a haemato-oncologist (a specialist of blood diseases). Besides chemotherapy that can cure 80% of acute lymphatic leukemia, a certain percentage of patients may need bone marrow transplant for cure.