Health Human Disease Blog

Laboratory evaluation of anemia starts with the hemogram, that is, the complete blood count (he­moglobin, hematocrit, white blood cell count, dif­ferential, platelet count, and red cell indices) plus the peripheral blood smear. In addition, initial evaluation should include a reticulocyte count, examination of the stool for occult blood, and uri­nalysis. Automated cell counters directly deter­mine the number and size (volume) of blood cells and measure hemoglobin chemically; the hema­tocrit is then derived from these values. This com­plete examination can be carried out on capillary blood from a fingerstick. Automated differential counters are available that report the white cell differential in absolute numbers based on scan­ning of large populations of leukocytes either on fixed smears or in cell suspensions. Nevertheless, the visual differential performed on stained smears remains an important method and permits evaluation of the morphology of individual leu­kocytes and of erythrocytes and platelets. Direct examination of the morphology of a stained peripheral blood smear is particularly important in evaluating abnormal cells, as in leukemia. An ad­vantage of automated cell counting is the ability to use the standard deviation of the variable being measured, e.g., red cell volume, to provide infor­mation on population heterogeneity, an important factor in certain disease states.

The red cell indices give information about the average red cell volume (MCV, mean corpuscular volume] and red cell hemoglobin content (MCH, mean corpuscular hemoglobin) or concentration (MCHC, mean corpuscular hemoglobin concen­tration). The MCV is the most useful, since it per­mits separation of microcytic anemia (MCV <80 cu fjim) from normocytic (MCV 80 to 100) and ma­crocytic anemias (MCV >100 cu ^m). These mor­phologic categories correlate well with several common types of anemia. Microcytosis most com­monly occurs in iron deficiency, thalassemia trait, and chronic renal insufficiency, whereas normo-cytosis accompanies acute blood loss. Macrocy-tosis is characteristic of nutritional anemias, in­cluding folic acid deficiency and vitamin B12 de­ficiency. Mild macrocytosis (MCV 100 to 110) may also be associated with hemolytic anemias with a raised reticulocyte count and with the re­fractory anemias found in myelodysplastic syn­dromes. The MCH is generally low in thalassemia trait, thalassemia, and iron deficiency; the MCHC may be high in spherocytic hemolytic anemias.

Inspection of the peripheral blood smear gives information about individual blood cells not read­ily obtained from the average values reported by ‘ the automated blood counters. The appearance and heterogeneity of red cells can be of diagnostic importance. For example, the microcytes of iron deficiency are relatively homogeneous, whereas in thalassemia major much more diversity in red cell size and shape occurs. In general, the further red cells diverge from the ideal shape (biconcave disc) and size (8 |xm diameter), the shorter their lifespan in the circulation. The appearance of sic­kle cells, cells with inclusion bodies, e.g., Howell-Jolly bodies (nuclear remnants) or basophilic stip­pling (RNA remnants), parasitized cells (e.g., ma­laria), microspherocytes, and schistocytes (e.g., microangiopathic anemias, disseminated intra­vascular coagulation) is rapidly appreciated by in­spection of the peripheral blood smear. Similarly, the appearance of individual leukocytes discloses blasts, hypersegmented polymorphonuclear cells, atypical lymphocytes, toxic granulation, and other morphologic abnormalities of disease gen­erally inaccessible to machine recording. Platelet clumping versus true thrombocytopenia and the appearance of very large or small platelets also adds clinically relevant information to the nu­merical counts.

Evaluation of the leukocyte and platelet counts is an integral part of investigating anemia, since low counts may signify marrow failure or replace­ment, and high counts maybe associated with leu­kemia or infection. Suspicion of pancytopenia or of marrow invasion with a pathological process should lead to a bone marrow examination.

The reticulocyte count measures the per cent of newly released erythrocytes in the circulating blood; these are larger than mature red blood cells and contain traces of endoplasmic reticulum, sig­nifying the continuing capacity for hemoglobin synthesis. After one to two days in the circula­tion, these methylene blue-stained traces of RNA disappear. Since the normal red cell life­span is 120 days, the normal reticulocyte count is approximately 1 per cent. Anemia increases the apparent reticulocyte count by decreasing the de­nominator by which the reticulocyte percentage is calculated (reticulocytes/1000 RBC); hence re­ticulocyte counts should be corrected to a “nor­mal” hematocrit of 45 (corrected reticulocyte count = retic count x patient’s hematocrit/45). Further corrections may be needed during severe anemias when reticulocytes circulate for longer than 24 hours. An elevated reticulocyte count (corrected) signifies increased erythropoietic ac­tivity, which may represent a normal response to bleeding, replacement of an appropriate hema-tinic such as iron, folate or vitamin B12, or a re­sponse to hemolysis. A very low reticulocyte count or absence of reticulocytes occurs after transfusion or in aplastic states.
Blood loss from the gastrointestinal tract is such a common cause of anemia that any initial eval­uation of anemia should include testing one to three stool specimens for occult blood. Because bleeding is often intermittent, it is best to obtain several stool specimens on different days. While blood loss into the urine is less common, it is nevertheless desirable to examine the urine for the presence of red cells or blood as well.

Pokerstars are the number one poker room with an amazing amount of tutorials.