This is the complete blood count test that is carried out to check your overall health and also to detect other disorders like anemia, leukemia or infection. The various components and features measured by this test are the red blood cells (those which carry blood), the white blood cells (those which fight infection), hemoglobin (the iron-rich protein that helps in carrying oxygen), platelets (the component that helps blood to clot). If the test shows an abnormal increase or decrease in cell count, it indicates that you are underlying medical condition and that you might need further evaluation.

Hematocrit is the total blood volume that is composed of red blood cells. This test determines whether you have too less or too many red blood cells in your blood and these two conditions can occur due to certain diseases. This test requires a sample of your blood which the lab technician puts into a device called centrifuge. This device spins the blood quickly in a test tube. The blood separates into three parts: the red blood cells, plasma (the fluid component) and the other blood cells. The test determines the proportion of the red blood cells. Hematocrit is also known as packed cell volume or PCV.

This test determines the amount of hemoglobin your blood has. Hemiglobin is the iron-rich protein in your blood that helps the red blood cells to carry oxygen to the various organs of your body and transport carbon dioxide back from the tissues to the lungs. A lower than normal hemoglobin level tells that you have low red blood cells count and that results in you being anemic. This can also be due to vitamin deficiency, chronic diseases or blood loss. A higher than normal hemoglobin level has several potential causes like a blood disorder named polycythemia vera, smoking, dehydration, burns, excessive vomiting or living in a high altitude.

This test is performed to determine if you have the sickle cell trait or the sickle cell disease. This is an inherited blood disease that causes the red blood cells to become deformed into a sickle shape. This deformity is caused by an abnormal type of hemoglobin named hemoglobin S while the normal hemoglobin is hemoglobin A. The red blood cells that have become sickled in shape are prone to faster destrution by the body than the normal blood cells. This leads to a condition called sickle cell anemia where there is an inadquate amount of oxyegen supply in the whole body. A method named high performance liquid chromatography (HPLC) determines the type of hemoglobin present in the blood sample. 

This type of anemia is related to the deficiency of vitamin B12 and folate. The red blood cells look underdeveloped and large. The platelets and the white blood cells also look abnormal too. The other tests preformed to determine the level of vitamin B1 deficiency are the antibodies test (in which the proportion of antibodies to intrinsic factor indicates whether you have pernicious anemia), the methylmelonic acid test (which determines the level of the substance methylmelonic acid in the blood which is usually higher in people with vitamin B12 deficiency) and the Schilling test (which determines whether you lack your intrinsic factor).  

Aplastic anemia occurs when the body stops producing enough new blood cells. When the levels of the white blood cells, red blood cells and platelets are very low, your doctor might suspect you have aplastic anemia. The doctor can also suggest to go for a bone marrow biopsy where the doctor uses a needle to draw out a small sample of bone marrow from a large bone in your body (such as the hip bone). Bone marrow of people with aplastic anemia will show a low blood cell count than normal. Aplastic anemia is a rare condition and it can develop at any age. 

Anemia from iron deficiency is a very common type of anemia. For this the regular blood test for hemoglobin, hematocrit and ferritin is done. The doctor, suspecting anemia due to bleeding in your stomach or intestines, will ask you to get the fecal occult blood test (FOBT), which checks if blood is there in your stool sample, colonoscopy to check your large intestines and endoscopy to identify stomach ulcers.

Special reliable blood tests like hemoglobin electrophoresis and quantitation of hemoglobin A2 and hemoglobin F can help us determine whether a person is thalassemia positive. Thalassemia means your blood having less hemoglibon, that is, red blood cells fewer than normal. Fewer red blood cells of thalassemia and low hemoglobin cause anemia, thereby causing fatigue. 

This will naturally need a sample of your bone marrow. Before the test is done, you will have to inform your doctor whether you are under any medication, if you are pregnant, if you have bleeding problems and if you are allergic to any medications. First a numbing medicine will be injected. The biopsy needle will also cause a brief pain and as the inside of the bone cannot be numbed, this test will surely cause some discomfort. The results will detect the cause of anemia, thrombocytopenia (fewer platelets) and abnormal white blood cells.