Hematopoietic Stem Cells

Stem cells that form blood (red blood cells) and immune cells (white blood cells) are called hematopoietic stem cells. These cells work towards renewing blood cells and producing billions of new blood cells every day through a process called Hematopoiesis. These cells are multi-potent cells that are present in the blood and bone marrow. Multi-potency is the ability to differentiate into all functional blood cells.

The two main characteristics of hematopoietic stem cells are that they can renew themselves and they can produce cells that in turn give rise to different types of blood cells. There lies a small challenge in identifying these cells as they look similar to ordinary white blood cells.

Hematopoietic stem cells are used to treat malignant and non-malignant diseases to replace and rebuild a patient's Hematopoietic system. These cells are used to treat diseases of blood. There are two types of hematopoietic stem cells, long term and short term. Once these cells are removed from the bone marrow, it is very difficult to differentiate them. However long term hematopoietic stem cells can differentiate themselves by renewing indefinitely whereas short term hematopoietic stem cells cannot renew themselves beyond about 6 months.

Understanding Hematopoietic stem cells

Hematopoietic stem cells are cells that are isolated from the bone marrow or blood. They can renew themselves and differentiate themselves into a variety of specialized cells. These cells can arise out of the bone marrow into circulating blood. They also have the special property of programmed cell death also known as apoptosis wherein the cells that are not required or detrimental get into a programmed self destruction mode.

Hematopoietic stem cells sources:

The major sources of hematopoietic stem cells from where they can be derived are:

Bone marrow: Bone marrow is identified as a potential source of hematopoietic stem cells.

Peripheral blood: Though bone marrow is a potential source, physicians these days prefer to source hematopoietic stem cells from peripheral blood. They harvest hematopoietic stem cells from circulating peripheral blood. The donor is injected with cytokine - which increases the migration of the hematopoietic stem cells from the bone marrow into the peripheral blood. The blood from the donor is drawn using intravenous method, the blood drawn is passed through a filtering system that extracts the white blood cells and returns the red blood cells back to the donor. Of these cells collected, 5 – 20% of the cells are hematopoietic stem cells.

Umbilical cord blood: The umbilical cord and the placenta is a rich source of hematopoietic stem cells. Researchers have also identified the embryonic stem cells and the fetal hematopoietic system as a rich source of hematopoietic stem cells. Cells extracted from fetal hematopoietic system are not being used clinically while the cells extracted from the embryonic stem cells are under extensive study.

Do hematopoietic stem cells from different sources vary ?

Considerable research is being conducted to understand hematopoietic stem cells. Hematopoietic stem cells extracted from tissues at early developmental stage have a greater ability to self replicate. They are well accepted by the immune system thus making it more useful for therapeutic transplantation.

Leukopenia

Leukopenia is a condition wherein the leukocyte count in the blood is low. Low WBC or White Blood Cells indicate decrease in disease fighting cells circulating in the blood. Some of the common causes for low WBC count:

Viral infections Any viral infections may disrupt bone marrow function for a short duration thus producing low counts of white blood cells. Infections like typhoid, influenza may lower the white blood cell count.

Congenital disorders may weaken bone marrow function, a WBC spectrum test can confirm any such congenital disorder.

Kostmann's syndrome is a congenital disorder wherein the neutrophil production is low.

Myelokathexis Neutrophils fail to enter the blood stream.

Infectious disease HIV destroys the WBC and leaves the person susceptible to infections.

Malnutrition

Vitamin or mineral deficiencies

Parasitic diseases

Autoimmune disorders may destroy white blood cells or bone marrow cells.

Aplastic anemia In this condition the bone marrow does not produce enough of any of the cells including white blood cells. This condition may set in all of a sudden or can develop and progress gradually. Few drugs, pregnancy, radiation therapy or chemotherapy can trigger this condition.

Lupus is an auto immune disease wherein the body fights with its own immune system thus destroying white blood cells.

Chemotherapy and radiation therapy are used to kill cancerous cells. They however destroy healthy white blood cells thus leaving the patient with low WBC count. This is one major reason why cancer patients are unable to fight diseases or infections in general.

Leukemia is a type of cancer wherein the body produces too many white blood cells that are abnormal. These white blood cells are not active white blood cells that can fight infections. People down with leukemia have low white blood cell count as their bone marrow is producing more of the abnormal white blood cells.

Cancer may also damage the bone marrow.

Hyperthyroidism An overactive thyroid can produce lower number of white blood cells. The medication used for thyroid can reduce the white blood cell count in the blood.

Liver disorder/Spleen disorder Hypersplenism, in which blood cells are destroyed prematurely by the spleen. An enlarged spleen also known as splenomegaly can trigger low white blood cell count.

Reticulocyte Count Test

Blood is a precious fluid. Plasma, white blood corpuscles and red blood corpuscles are the three kinds of cells in the blood. The blood cells are normally made in the bone marrow. To know the level of red blood cells in the blood, reticulocyte count test is done.

Reticulocyte Count Test

Reticulocyte are immature red blood cells made by the bone marrow. Reticulocytes are in the blood for two days before developing into mature cells. Reticulocyte count test is done to determine if red blood cells are being made in the bone marrow at an appropriate rate. The count indicates how quickly reticulocytes are being produced and released by the bone marrow.

Need for Reticulocyte count test

Paleness, tiredness, weakness, shortness of breath, and/or blood in the stool are symptoms when doctors recommend Reticulocyte count test to:

• Assess the functioning of bone marrow i.e. if enough red blood cells are made by the bone marrow.
  
• Diagnose and distinguish the different kinds of anemia and the reasons for anemia, if it is due to fewer red bloods or due to great loss of red blood cells.
  
• Evaluate reasons for chronic bleeding and or/blood in the stool.
  
• Monitor progress after chemotherapy, bone marrow transplant, treatment for iron deficiency etc.
  
• Determine the degree and rate of increased number of RBCs and elevated hemoglobin (rare occurrence) and hematocrit.

Reticulocyte count test - Preparation

There isn't any specific preparation required before Reticulocyte count test. However, it is recommended to check with health care provider if any specific pre test preparation is needed. Those who have had a recent blood transfusion should inform the doctor. This can affect test results. Important information to be shared with the doctor is about medicines being taken. Women who are pregnant and mothers who are breastfeeding infants should talk to doctor before opting for the test.

Reticulocyte count test Method

The test result is available few hours after collecting blood or the next day. An elastic band is wrapped around the upper arm to stop the flow of blood. Sample of blood from the vein of the arm is taken. A drop of blood is placed on a slide, smeared, stained and is examined under a microscope. This is the manual method. Automated methods that allow for greater number of cells to be counted are most likely to replace the manual method.

Reticulocyte count test result Interpretation

The number of reticulocytes is compared to the total number of red blood corpuscles (RBC) and is reported as a percentage of reticulocytes.

Reticulocyte (%) = [Number of Reticulocytes / Number of total Red Blood Cells] X 100

In a healthy adult person, the normal range is 0.5% to 1.5%. In kids, the normal range is 3% to 6%. This is a stable percentage. The normal range may slightly vary.

High reticulocyte count suggests more red blood cells are being made by the bone marrow. This could be due to acute bleeding, chronic blood loss, hemolytic anemia, kidney disease and potentially a fatal blood disorder in the fetus or new born - erythroblastosis fetalis (Erythroblastosis Fetalis refers to a serious blood disorder in infants - Rh incompatibility disease and ABO incompatibility disease) or hemolytic disease. Also, the count increases post treatment for certain anemia like iron deficiency anemia, pernicious anemia, or folic acid deficiency anemia.

Erythroblastosis Fetalis refers to a serious blood disorder in infants - Rh incompatibility disease and ABO incompatibility disease. Low reticulocyte count suggests fewer red blood cells are being made by the bone marrow. This can be due to aplastic anemia or iron deficiency anemia. Other instances such as exposure to radiation, a chronic infection or due to intake of certain medicines (drug toxicity) can lead to low count.

The reticulocyte count increases temporarily during pregnancy. The count is high in newborns but within few weeks the count drops to adult levels. In case the result is abnormal more tests may be administered for further analysis.