Test: Total Hemoglobin (Hgb or Hb)
A test used to determine the amount of hemoglobin in the blood. Hgb is the pigment part of the erythrocyte, and the oxygen-carrying part of the blood.
A Low hemoglobin level indicates anemia. Estimates of Hgb in each RBC are moderately important when determining the total blood Hgb. However, hemoglobin findings are even more dependent upon the total number of RBC's. In other words, for the diagnosis of anemia, the number of RBC's is as important as the hemoglobin level.
Blood hemoglobin level has become a "routine" lab test for most patients admitted to hospitals today. Hgb is obviously important for the diagnosis of anemia and hemorrhage. It is equally important for diagnosing many lesser known diseases.
The test can be performed upon capillary blood, such as drawn from the finger stick. The test is often performed along with other tests, thereby requiring a larger specimen of blood, as from venipuncture. Hemoglobin in the body is dependent upon amounts of iron. A lack of available iron causes one type of anemia, due to the reduced production of hemoglobin. Remember that in the strictest sense, anemia is not in itself a diagnosis, but rather a symptom that there is something else wrong in the body. For example, malnutrition (low iron levels), would be the diagnosis of the patient, not just the anemia. The secondary diagnosis would be anemia, but malnutrition must be treated in order to "cure" the anemia.
Fetal Hb (Hb F), is a normal Hb product in the red blood cells of a fetus and in smaller amounts in infants. It constitutes 50% to 90% of Hb in a newborn; the remaining Hb consists of Hb A1 and Hb A2 the Hb in adults.
Under normal conditions, the body ceases to manufacture fetal Hb sometime during the first year of life, and from that point on manufactures adult Hb. If this changeover does not occur and fetal Hb continues to constitute more than 5% of the Hb after age six months, an abnormality should be suspected, particularly thalassemia.
VARIATIONS OF HEMOGLOBIN TYPE AND DISTRIBUTION (in adults)
Test: Hemoglobin Electrophoresis
Hemoglobin electrophoresis is probably the most useful laboratory method for separating and measuring normal and some abnormal Hb. Through electrophoresis, different types of Hb are separated to form a series of distinctly pigmented bands in a medium (cellulose acetate or starch gel). Results are then compared with those of a normal sample.
Hb A (same as Hb A1), Hb A2, Hb S, Hb C, and Hb F are routinely checked, but the laboratory may change the medium or its pH to expand the range of the test. This test, by measuring the different types of Hb, is used to detect normal and abnormal types of hemoglobin, to aid in the diagnosis of thalassemia, and to aid in the diagnosis of sickle cell disease or trait.
**For normal or reference values, see the chart above.
Test: Hematocrit Hct
The hematocrit measures percentage by volume of packed red blood cells in a whole blood sample. For example, a HCT of 40% indicates that a 100-ml sample of blood contains 40 ml of blood cells. Packing is achieved by centrifuging anticoagulated whole blood in a capillary tube so that the cells are tightly packed without hemolysis.
Two small specimens of blood are obtained and compared. They are the same amount of blood exactly. One specimen is then centrifuged and subsequently compared to the first specimen. A percentage is then obtained from that comparison. This comparison is the hematocrit, Hct. The value of the hematocrit is dependent upon the number of RBC's. If the Hct is abnormal, then the RBC count is possibly abnormal. If the RBC count turns out to be normal, then the average size of the RBC is probably too small. Shock, hemorrhage, dehydration, or excessive IV fluid administration can reduce the Hct.
As you can see, there are many factors which can influence the results of the hematocrit test. However, this is still a good baseline lab test for the patient. It helps the physician to diagnose and to treat the patient with any disease which will lower or raise the Hct levels.
Test: Red Blood Cell Count RBC count
A count of actual (or estimated) number of RBC's per cubic mm of whole blood.
The RBC count is useful for determining such problems as anemia and hemorrhage. In combination with other hematology tests, it can be quite useful for diagnosis. This test can also give an indirect estimate of the hemoglobin levels in the blood. RBC's are actually "Red Blood Corpuscles," (non-nucleated cells). The term corpuscle indicates that it is a mature Red Blood Cell. Once the immature cell has matured, it is then, and only then, capable of carrying oxygen. It is then also not "technically" a cell anymore. Once it has matured, it loses its nucleus and can no longer be properly termed a cell. It would be called a corpuscle. However, everyone still refers to them as RBC's (cells). The source of the specimen is whole blood, capillary, or venous blood.
Test: Red Cell Indices (Wintrobe Indices)
A report of the individual characteristics of the RBC. The following are those characteristics which are used to indicate anemia. If abnormal findings are present, the anemias can be defined as macrocytic, microcytic, hypochromic, others. When this is discovered, the exact cause of the anemia can be determined more easily.
The following are all part of indices:
1. MCV - Mean Corpuscular Volume
The volume of the average RBC
Normal Value: 80-94 u3 (cubic microns)
The MCV indicates the relative size of the RBC's. It does not indicate anything else about the cell. Several different types of anemias can be classified as micro- or macrocytic anemias. This test can direct the MD toward those types of anemias which alter the MCV results.
2. MCH - Mean Corpuscular Hemoglobin: (Weight of hemoglobin in each cell)
Normal Value: 27-31 uuGrams (micro micro Grams)
3. MCHC - Mean Corpuscular Hemoglobin Concentration
Concentration of hemoglobin in the average RBC
The MCHC is dependent upon the size of the RBC as well as the amount of hemoglobin in each cell. Certain diseases and anemias will alter the RBC count and/or the amount of hemoglobin in the cell. The MCHC is not as dependent upon the RBC count as the other tests in this section. Therefore, the MCHC can be useful for the diagnosis of such conditions which are not dependent upon the number of RBC's.
The nursing implications for these tests are numerous. To the nurse, most cases of anemia are quite apparent. They are caused by hemorrhage, malnutrition, etc. However, the Indices can be used to help diagnose the less common types of anemias. Nursing care will then be determined according to the needs of that particular patient.
Test: Reticulocyte Count (Retic count)
This is a test for the estimation of the actual numbers of reticulocytes in the blood. Reticulocytes are the immature RBC's.
Normal Values: approx 1% of normal RBC count (50,000); Results vary; range 0.5% to 1.5%
The retic count is an indication of the production of RBC's by the bone marrow. An increase from the normal, usually indicates the body is responding to such pathologies as hemorrhage, anemia, hemolysis, or other such disease process. Decreased retic count may be indicative of aplastic anemia or any related disease.
The retic count is also examined for those persons working near any type of radioactive materials. The nurse should remember that the body tries to compensate for such conditions as the hemolytic and macrocytic conditions mentioned above. A large number of retics will be seen after the treatment has begun for pernicious anemia, in which large numbers will be produced as an attempt to bring to maturity, large numbers of RBC's.
Test: Sickle Cell Test
The sickle cell test, also known as the Hb S test, is used to detect sickle cells, which are severely deformed, rigid erythrocytes that may slow blood flow. Sickle cell trait (characterized by heterozygous Hb S) is found almost exclusively in people of African ancestry. It is present in nearly 8% of African Americans.
Although this test is useful as a rapid screening procedure, it may produce erroneous results. Hb electrophoresis should be performed to confirm the diagnosis if sickle cell disease is strongly suspected.
**See Hemoglobin electrophoresis test earlier in this chapter.
Test: Iron and Total Iron-binding Capacity
Iron is essential to the formation and function of hemoglobin, as well as many other heme and nonheme compounds. After iron is absorbed by the intestine, it is distributed to various body compartments for synthesis, storage, and transport. Serum iron concentration is normally highest in the morning and declines progressively during the day. Thus, the sample should be drawn in the morning.
An iron assay is used to measure the amount of iron bound to transferrin in blood plasma. Total iron-binding capacity (TIBC) measures the amount of iron that would appear in plasma if all the transferrin were saturated with iron.
Serum iron and TIBC are of greater diagnostic usefulness when performed with the serum ferritin assay, but together, these tests may not accurately reflect the state of other iron compartments, such as myoglobin iron and the labile iron pool. Bone marrow or liver biopsy, and iron absorption or excretion studies may yield more information.
TIBC, Total Iron-binding capacity:
Ferritin is a major iron-storing protein found in reticuloendothelial cells. It normally appears in small quantities in serum. In healthy adults, serum ferritin levels are directly related to the amount of available iron stored in the body and can be measured accurately by radioimmunoassay.
Normal serum Ferritin values will vary with age. Remember to check with your lab, as normal values may be different in different labs. The blood is collected via venipuncture in a standard 10-ml red-top tube. A random blood specimen is used. No special instructions need to be given to the patient except for explaining the procedure. Recent blood transfusions may elevate serum ferritin levels.
Increased Serum Ferritin Levels: may indicate acute or chronic hepatic disease, iron overload, leukemia, acute or chronic infection or inflammation, Hodgkin's Disease, or chronic hemolytic anemias.
Slight increase, or normal Ferritin Level: may indicate chronic renal disease
Decreased serum Ferritin Levels: may indicate chronic iron deficiency
Test: ESR--Erythrocyte Sedimentation Rate
The ESR measures the time required for erythrocytes from a whole blood sample to settle to the bottom of a vertical tube. Factors influencing the ESR include red cell volume, surface area, density, aggregation, and surface charge. The sample must be examined within 2 hours of collection and it must be handled gently, no clotting of sample must take place.
Normal values: 0-20 mm/hr (gradually increase with age)
The ESR is a sensitive, but nonspecific test that is frequently the earliest indicator of disease. It often rises significantly in widespread inflammatory disorders due to infection or autoimmune mechanisms. Such elevations may be prolonged in localized inflammation and malignancies.
Increased ESR: may indicate pregnancy, acute or chronic inflammation, tuberculosis, rheumatic fever, paraproteinemias, rheumatoid arthritis, some malignancies, or anemia.
Decreased ESR: may indicate polycythemia, sickle cell anemia, hyperviscosity, or low plasma protein.
Test: Osmotic Fragility
Osmotic fragility measures red blood cell (RBC) resistance to hemolysis when exposed to a series of increasingly dilute saline solutions. The sooner hemolysis occurs, the greater the osmotic fragility of the cells.
Purpose of test - The purpose of this test is to help diagnose hereditary spherocytosis and to supplement a stained cell examination to detect morphologic RBC abnormalities.
Normal results: Osmotic fragility values (percentage of RBC's hemolyzed) are determined by the tonicity of the saline. Reference values for the different tonicities are as follows:
0.5 g/dl sodium chloride (NaCl) solution (unincubated)
0.6 g/dl sodium chloride solution (incubated)
0.65 g/dl sodium chloride solution (incubated)
0.75 g/dl sodium chloride solution (incubated)
Low osmotic fragility (increased resistance to hemolysis) is characteristic of thalassemia, iron deficiency anemia, and other red blood cell disorders in which codocytes (target cells) and leptocytes are found. Low osmotic fragility also occurs after splenectomy.
High osmotic fragility (increased tendency to hemolysis) occurs in hereditary spherocytosis, in spherocytosis associated with autoimmune hemolytic anemia, severe burns, chemical poisoning, or in hemolytic disease of the newborn (erythroblastosis fetalis).
Test: WBC count--White Blood Cell Count (Leukocyte count)
A laboratory test that counts the actual number of WBC's in the blood.
Normal Values: total WBC: 4,500 to 10,500
BASIC TYPES OF WBC'S:
As we all know, WBC's are our body's first line of defense against invading bacteria and most other harmful organisms. This test (WBC), measures the total number of all types of WBC's. Further examination of the different types and numbers of cells present, could tell much about the state of the body's defense system. WBC count will normally vary as much as 2,000 on any given day.
Test: Differential Cell Count also known as "diff" or "differential"
Laboratory test that counts actual numbers of different types of WBC's.
The following chart gives the normal values for each type of WBC. Interpretation of the results of the differential must always be done with the total number of WBC's in mind.
The WBC differential evaluates the distribution and morphology of white blood cells. Therefore, it provides more specific information about a patient's immune system than the WBC count alone. In the differential test, the lab classifies 100 or more white cells in a stained film of peripheral blood according to two major types of leukocytes. They are: (1) Granulocytes (neutrophils, eosinophils, basophils); (2) non-Granulocytes (lymphocytes, monocytes). The percentage of each type is then determined.
The differential count is the relative number of each type of white cell in the blood. By multiplying the percentage value of each type, by the total WBC count, the lab obtains the absolute number of each type of white cell. Although little is known about the function of eosinophils in the blood, abnormally high levels of them are associated with various types of allergic disorders and reactions to parasites. In such cases, the eosinophil count is sometimes ordered as a follow-up to the white cell differential. This test is also appropriate if the differential WBC count shows a depressed eosinophil level.
Interpreting the Differential
In order to interpret the results of the WBC and the Differential, the nurse must consider both relative and absolute values of the differential. Considered alone, relative results may point to one disease while masking the true pathology that would be revealed by considering the results of the white cell count.
For example, consider a patient whose white blood cell (WBC) count is 6000/ul and whose differential shows 30% neutrophils and 70% lymphocytes. His relative lymphocyte count would seem to be quite high (lymphocytosis), but when this figure is multiplied by his white cell count (6000 x 70% = 4,200 lymphocytes/ul), it is well within normal range.
The patient's neutrophil count, however, is low (30%), and when this is multiplied by the white cell count (6,000 x 30% = 1,800 neutrophils/ul), the result is a low absolute number. This low result indicates decreased neutrophil production, which may mean depressed bone marrow.
Decreased by: (unknown)
RBC lab values, along with the indices, are used to diagnose anemia and to define the type of anemia present. The lab values are calculated and compared for the individual characteristics of the blood cells.
When the individual characteristics of the cells are determined, you can then decide if the condition is hemorrhagic or another type of anemia.
One should ask the following questions in order to isolate the type of anemia:
Nursing implications related to clotting studies are numerous. An increase in clotting of blood or a decrease in clotting ability will be considered the two main problems of coagulation of the blood.
Following is a summary of the overall phases of blood clotting. Circulating blood generally has two main inactive proteins relating to clotting. These are prothrombin and fibrinogen. It must also be remembered that platelets stimulate the clotting process.
Blood Clotting Process
Test: Platelet Count
A test which is a direct count of platelets (thrombocytes) in whole blood.
Normal Values: 150,000 to 350,000 per mm3 (cubic mm)
Platelets normally increase in persons living at high altitudes for extended periods of time. They also increase with persistent cold temperatures, and during strenuous exercise and excitement. The count decreases just prior to menstruation.
Test: Prothrombin Time PT or Pro Time
This test is a measure of phase III of the clotting process. The PT may give false readings due to some other clotting defects. However, it is usually indicative of a phase III problem.
Normal values: (child or adult): 11-15 seconds or 70%-100% (depends on method used)
Prothrombin is also known as factor II of the coagulation factors. It is produced by the liver and requires vitamin K for its synthesis. In liver disease, PT is usually prolonged. The test requires 7 to 10 ml of blood with an anticoagulant in the blood tube. It can be collected in a black-top tube (sodium oxalate in the tube), or blue-top tube (sodium citrate in the tube). The most common is the blue-top tube, the specimen must be tested within 4 hours of collection and is usually packed in ice and delivered to the lab quickly. This is a very common lab test and is usually performed as a routine hospital admission screening test. A high-fat diet may cause decreased PT, and alcohol can cause an increased PT result.
Test: Partial Thromboplastin Time PTT
A test similar to the PT, the PTT is also used to detect clotting abnormalities. APTT, Activated PTT, similar to PTT but is more sensitive than PTT test; it will help to identify the defective factor, if one is defective.
*these results may vary due to test methods in different hospitals.
The PTT is very similar to the PT. It is used to detect Phase II defects in the clotting process. It will usually detect deficiencies in all clotting factors except factors VII and XIII. It is usually performed for monitoring Heparin therapy. Heparin doses are usually adjusted according to the PTT test results. The PTT is usually more sensitive than the PT test.
Test: Bleeding Time
A raw measurement of the time needed for an artificially produced skin puncture to stop bleeding.
Hodgkin's disease is suspected if there is decreased bleeding time. Prolonged rate may indicate: thrombocytopenic purpura, platelet abnormality, vascular abnormality, leukemia, severe liver disease, DIC disease, aplastic anemia, factor deficiencies (V, VII, XI), Christmas disease, hemophilia. The following drugs can affect bleeding time: aspirin, dextran, mithramycin, coumadin, streptokinase-streptodornase (fibrinolytic agent). Aspirin, alcohol, and also anticoagulants may increase bleeding time.
This test is usually inconclusive. It can however, be helpful for diagnosing capillary abnormalities and other disorders. For detecting other clotting problems, this test will usually show a normal result. This test is usually just a general screening test.
Test: TGT, Thromboplastin Generation Time
A test for phase II clotting defects. It tests the ability of the patient to produce thromboplastin.
This test is very complicated and only a few large laboratories will perform this test. The TGT has the ability to exactly pinpoint the defect in the clotting process. This fact can make the TGT a very valuable test under certain circumstances.
Test: Plasma Fibrinogen
A test for the level of circulating plasma fibrinogen.
This test can be very valuable for helping diagnose disorders which can cause lowered levels of the fibrinogen. It is also useful for detecting substances which destroy fibrinogen (fibrinolysins).
Discussion of Coagulation Tests
The tests mentioned here are commonly used in hospitals today. There are many other coagulation tests available, most of which are complicated, expensive, and usually only performed at large medical centers. Many of those specialized tests are used only after simpler screening tests are performed.
The nurse should always remember to obtain a very detailed history from the patient. The history can be most useful in helping the MD make an accurate diagnosis.
Many times the patient may not speak freely with the physician or may have forgotten some important detail or symptom. An observant nurse can possibly help with the medical diagnosis and possibly save the patient extra hospitalization and/or unnecessary testing.
As far as the mechanics of the tests are concerned, there is little for the nurse to do in order to prepare the patients. The nurse should always "warn" the patient that the blood will be drawn, or that they will be injected with something, if it is part of the test. However, most coagulation studies are done with a specimen of blood drawn either randomly or at a special time of the day.
The specimen of blood will probably have an anticoagulant in it or in the collection tube and most specimens will either have to be iced or brought to the lab quickly for analysis.