Complete Blood Count: Assessment, Analysis, and Associated Dental Management Guidelines
HEMATOPOIETIC SYSTEM OVERVIEW
The hematopoietic stem cell resides predominantly in the bone marrow and, very particularly, in the pelvis and the long bones. The hematopoietic stem cell differentiates and matures to form the three cell lines found in the blood: the white blood cells (WBCs), red blood cells (RBCs), and platelets (Plts). Discussion in this section centers on disease states associated with these cell lines.
COMPLETE BLOOD COUNT COMPONENTS
The following are components of the complete blood count (CBC):
- The total white blood cell (WBC) and red blood cell (RBC) count
- Hemoglobin (Hb)
- Hematocrit (Hct)
- Mean corpuscular volume (MCV)
- Mean corpuscular hemoglobin (MCH)
- Mean corpuscular hemoglobin concentration (MCHC)
- Red cell distribution width (RDW)
- Platelet count
- WBC differential
The WBC differential count consists of neutrophils plus bands (immature neutrophils), lymphocytes, monocytes, eosinophils, and basophils. The total RBC count, Hb, Hct, MCV, MCH, MCHC, and RDW help analyze some of the common RBC-related conditions encountered such as anemia, polycythemia, and hemochromatosis. The reticulocyte count, which is not part of the CBC, is also evaluated to determine the status of anemia, polycythemia, and hemochromatosis.
The total WBC and the WBC differential counts help analyze infection, inflammation, underlying allergy states, leukemias, lymphomas, and so on. Serial WBC with differential (WBC w/diff.) helps determine the patient’s response to treatment. The platelet (Plt) count helps assess the number of platelets available for primary or platelet-associated hemostasis. The Plt count also highlights any platelet-related disorders such as thrombocytopenia (decreased Plt count) or thrombocytosis (increased Plt count).
The bleeding time (BT), which is not a part of the CBC, shows the functioning capacity of the platelets. The function of the platelets is to stick together during primary hemostasis and arrest the bleeding when injury occurs.
The Red Blood Cell (RBC)
The RBC count can be normal or decreased depending on the acuteness of the anemia. A decreased RBC count can occur because of decreased RBC production by the bone marrow or overdestruction of the RBCs, as with hemolysis. The average life span of the normal RBC is 120 days. The normal RBC count for male patients is 4.5–5.9 million/μL; for female patients it is 4.0–5.2 million/μL.
All mature RBCs contain hemoglobin (Hb). Hemoglobin in the fetus is hemoglobin F, and following birth it changes to hemoglobin A. Hemoglobin A contains two alpha (α) chains and two beta (β) chains. Anemia is associated with a reduction in the hemoglobin content. A reduction in the hemoglobin content results in tissue hypoxia and poor wound healing. The normal hemoglobin value in males is 13.5–17.5 g/dL; in females it is 12.0–16.0 g/dL.
Hematocrit is expressed as a percentage and it reflects the red cell mass divided by the total blood volume. The hematocrit can also be estimated by multiplying the hemoglobin by 3. Anemia is associated with a decreased hematocrit. The hematocrit thus helps establish the extent of anemia. The normal hematocrit value is 37–47%.
Mean Corpuscular Volume (MCV)
MCV measures the size/volume of the mature RBC. The red cells are said to be microcytic when the MCV is below normal value and macrocytic when the MCV is above normal value. Microcytic cells occur when there is a problem with hemoglobin synthesis, affecting either the heme or globin components. Iron deficiency is the leading cause for microcytic cells, followed by thalassemia. Macrocytic cells occur when there are problems associated with DNA synthesis. Common causes for macrocytic cells are pernicious anemia, B12 or folic acid deficiency, HIV/AIDS medications, and some cytotoxic drugs. The normal MCV is 80–100 fL/RBC.
Mean Corpuscular Hemoglobin (MCH)
MCH measures the average amount of hemoglobin in each mature RBC. Microcytic anemias are associated with low MCH, and the macrocytic anemias are associated with “increased” MCH. The “increased” MCH in the macrocytic cell is a relative increase caused by an increase in cell size. That the increase is relative is further confirmed by the associated presence of a normal mean corpuscular hemoglobin concentration (MCHC). The normal MCH is 26–34 pg/RBC.
Mean Corpuscular Hemoglobin Concentration (MCHC)
MCHC measures the hemoglobin concentration in a given volume of packed RBC. The MCHC is labeled as hypochromic when the MCHC is decreased, and this hypochromic pattern is associated with the microcytic anemias. The MCHC is listed as normochromic when the MCHC is normal and this pattern is associated with the macrocytic anemias. MCHC is calculated as follows: MCHC = Hemoglobin + Hematocrit. The normal MCHC is 31–37 g/dL.
MCV-MCHC Values and Associated RBC Types
The MCV and MCHC patterns on the CBC help categorize the RBC types as the following:
- Microcytic, hypochromic cells
- Macrocytic, normochromic cells
- Normocytic, normochromic cells
Red Cell Distribution Width (RDW)
RDW measures the anisocytosis (RBCs of unequal size) associated with the RBCs. Increased anisocytosis is associated with an increased RDW. The greater the number of immature RBCs in the circulation, the greater will be the RDW.
Note that the immature RBCs are larger in size when compared to the mature RBCs, and the immature RBCs do not carry oxygen. The RDW also helps differentiate between iron deficiency anemia and thalassemia minor. The RDW is increased in iron deficiency anemia and normal in thalassemia minor. An increased RDW in the presence of a decreased RBC count indicates an active bone marrow. This pattern is frequently seen with many of the anemias, indicating that the body is trying to compensate. A decreased RDW along with a decreased RBC count indicates a depressed bone marrow. The normal RDW is 11.5–14.5%.
The reticulocyte count measures erythropoietic activity and the response of the bone marrow to anemia. Immature nucleated RBCs abound in the circulation when the reticulocyte count is increased. Hemolysis is associated with an increased reticulocyte count. Hemolysis can occur with any inherited or hemolytic anemias: sickle-cell anemia, thalassemia, G6PD deficiency anemia, and hereditary spherocytos/>