Hematology part 1 answer

Answers to Part 1 Questions 

1. A 

Insufficient centrifugation does not pack down the red blood cells; therefore, the Hct, which is the volume of packed cells, will increase. 

2. A 

A mature erythrocyte is approximately 7–8 μm in diameter. Variation in normal size is denoted by the term anisocytosis. Hypochromia is a term that indicates increased central pallor in erythrocytes, and poikilocytosis denotes variation in red cell shape. 

3. A 

The iliac crest is the most frequently used site for bone marrow aspiration and biopsy. This site is the safest and most easily accessible, with the bone just beneath the skin, and neither blood vessels nor nerves are in the vicinity. 

4. B 

MCV is the average “volume” of the red cells. This is obtained by dividing the Hct or packed cell volume (PCV) by the red blood cell (RBC) count in millions per microliter of blood and multiplying by 10. The MCV is expressed in cubic microns (μm3) or femtoliters (fL). 

5. A 

Variation in shape of the erythrocytes on a peripheral blood smear is poikilocytosis. Anisocytosis refers to a change in size. Hypochromia is an increase in central pallor in erythrocytes. Polychromasia describes the bluish tinge of the immature erythrocytes (reticulocytes) circulating in the peripheral blood.

6. C 

MCHC is the average concentration of Hgb in red cells expressed as a percentage. It expresses the ratio of the weight of Hgb to the volume of erythrocytes and is calculated by dividing Hgb by the Hct, and then multiplying by 100. A decreased MCHC indicates that cells are hypochromic. In this example, (15 ÷ 47) × 100 = 31.9%. The reference range for MCHC is 32%–36%. 

7. A 

The formula used for calculating manual cell counts using a hemacytometer is: Number of cells counted × dilution factor × depth factor (10) divided by the area. In this example, 36 × 10 × 10 = 3600 ÷ 9 = 400/mm3or 0.4 × 109/L. 

8. D 

Siderocytes are red cells containing iron granules and are visible when stained with Prussian blue. 

9. C 

Excessive anticoagulant causes shrinkage of cells; thus, the Hct will be affected. RBC and WBC counts remain the same, as does the Hgb content. 

10. B 

RBC count = number of cells counted × dilution factor × depth factor (10), divided by the area. In this example, 336 × 200 × 10 = 672,000 ÷ 0.2 = 3.36 × 106/mm3 = 3.36 × 1012/L.

11. D 

Neutrophils are highly phagocytic and release lysozymes, peroxidase, and pyrogenic proteins. Eosinophils migrate to sites where there is an allergic reaction or parasitic infestation, releasing peroxidase, pyrogens, and other enzymes, including an oxidase that neutralizes histamine. They are poorly phagocytic and do not release lysozyme.

12. B 

In anemic states, the reticulocyte percentage is not a true measure of reticulocyte production. The following formula must be applied to calculate the corrected (for anemia) reticulocyte count. Corrected reticulocyte count = reticulocytes (%) × Hct ÷ 45, the average normal Hct. In this case, 7 × (20 ÷ 45) = 3.1. 

13. A 

Osmotic fragility is decreased when numerous sickle cells and target cells are present and is increased in the presence of spherocytes. Spherocytes are a prominent feature of hereditary spherocytosis (HS), hemolytic disease of the newborn, and acquired hemolytic anemia. The osmotic fragility test is increased in the presence of spherocytes, whereas this test is decreased when sickle cells, target cells, and other poikilocytes are present. 

14. A 

The pH of the buffer is critical in Romanowsky stains. When the pH is too low (<6.4), the red cells take up more acid dye (eosin), becoming too pink. Leukocytes also show poor nuclear detail when the pH is decreased. 

15. B 

Heinz bodies are irregular, refractile, purple inclusions that are not visible with Wright’s stain but show up with supravital staining. The other three inclusions can be detected with Wright’s stain. 

16. B 

The MCH = Hgb × 10/RBC count and is not affected by the Hct. The MCV = Hct × 10/RBC count, and MCHC = Hgb × 100/Hct; therefore, an erroneous Hct will affect these parameters. Centrifugal force for microhematocrit determination should be 12,000 g for 5 min in order to avoid error caused by trapped plasma. The red cell distribution width (RDW) is calculated by electronic cell counters and reflects the variance in the size of the red cell population. Electronic cell counters calculate Hct from the MCV and RBC count. Therefore, the RDW would be affected by an erroneous MCV. 

17. B 

The manual reticulocyte count involves the counting of 1,000 RBCs. The Miller disk is a reticle (grid) that is placed in the eyepiece of the microscope and divides the field into two squares, one being nine times larger in size than the other. Reticulocytes are enumerated in both the squares. Mature red cells are counted in the smaller one.

18. C 

The MCV, MCH, and MCHC are all within the reference interval (normal range); hence, the erythrocytes should be of normal size and should reflect normal concentrations of Hgb. Therefore, the anemia is normocytic normochromic. 

19. A 

EDTA and sodium citrate can be used without any effect on the ESR. Anisocytosis and poikilocytosis may impede rouleaux formation, thus causing a low ESR. Plasma proteins, especially fibrinogen and immunoglobulins, enhance rouleaux, increasing the ESR. Reference ranges must be established for different caliber tubes. 

20. B 

The reticulum within the reticulocytes consists of ribonucleic acid (RNA), which cannot be stained with Wright’s stain. Supravital staining with new methylene blue is used to identify the reticulocytes. 

21. A 

Electronic cell (Coulter) counters use the principle of electrical impedance. Two electrodes suspended in isotonic solutions are separated by a glass tube having a small aperture. A vacuum is applied, and as a cell passes through the aperture it impedes the flow of current and generates a voltage pulse. 

22. C 

The automated hematology analyzers enumerate all nucleated cells. NRBCs are counted along with WBCs, falsely elevating the WBC count. To correct the WBC count, determine the number of NRBCs per 100 WBCs. Corrected WBC count = (uncorrected WBC count ÷ [NRBC’s + 100]) × 100. 

23. B 

The RDW parameter correlates with the degree of anisocytosis seen on the morphological examination. The reference range is 11.5%–14.5%.

24. C 

Spherocytes have a decreased cell diameter and volume, which results in loss of central pallor and discoid shape. The index most affected is the MCHC, usually being in excess of 36%. 

25. C 

Standard deviation(s) describes the distribution of a sample of observations. It depends upon both the mean (average value) and dispersion of results and is most influenced by reproducibility or precision. Because s is influenced by the mean and expressed as a percentage of the mean, the coefficient of variation ([s ÷ mean] × 100) can be used to compare precision of tests with different means (e.g., WBC and RBC counts or low vs. high controls). 

26. D 

Deoxyhemoglobin is the physiological Hgb that results from the unloading of oxygen by Hgb. This is accompanied by the widening of the space between β–chains and the binding of 2,3-diphosphoglycerate (2,3-DPG) on a mole-for-mole basis. 

27. A 

Acidosis is associated with a shift to the right of the oxyhemoglobin dissociation curve and, therefore, increased oxygen release (decreased affinity of Hgb for oxygen). Alkalosis does the opposite. Multiple blood transfusions shift the curve to the left because the transfused blood is low in 2,3-DPG. Hgb S and Hgb C do not change the affinity of oxygen for hemoglobin; however, many hemoglobinopathies do. For example, Hgb Kansas causes a right shift and Hgb Chesapeake causes a left shift of the oxyhemoglobin dissociation curve. 

28. B 

Lymphocytes constitute the majority of the nucleated cells seen. The bone marrow in aplastic anemia is spotty with patches of normal cellularity. Absolute granulocytopenia is usually present; however, lymphocyte production is less affected. 

29. C 

The normal adult percentage of lymphocytes in a white cell differential is between 20% and 44%, although normal ranges vary by institution, patient population, and testing methodology. This range is higher in the pediatric population.

30. A 

There is a relative neutropenia in children from ages 4 months to 4 years. Because of this, the percentage of lymphocytes is increased in this population. This is commonly referred to as a reversal in the normal differential percentage (or inverted differential). 

31. C 

A relative monocyte count of 15% is abnormal, given that the baseline monocyte count in a normal differential is between 1% and 8%. An increased monocyte count may signal a myeloproliferative process such as chronic myelomonocytic leukemia, an inflammatory response, or abnormal lymphocytes that may have been counted as monocytes by an automated cell counter. 

32. D 

In normal erythrocytic maturation, Hgb formation in the late polychromatic normoblast stage gives the cytoplasm a prominent pink coloration. The red cell continues to produce Hgb throughout the reticulocyte stage of development. 

33. D 

Increases in 2,3-DPG, acidosis, hypoxia, and a rise in body temperature all shift the hemoglobin-oxygen dissociation curve to the right. In anemia, although the number of RBCs is reduced, the cells are more efficient at oxygen delivery because there is an increase in red cell 2,3-DPG. This causes the oxyhemoglobin dissociation curve to shift to the right, allowing more oxygen to be released to the tissues. 

34. C 

The structure of Hgb H is β4. Hgb H disease is a severe clinical expression of α–thalassemia in which only one α–gene out of four is functioning. 

35. D 

Autoagglutination at room temperature may cause a low RBC count and high MCV from an electronic counter. The Hct will be low because it is calculated from the RBC count. Low RBC count and low Hct cause falsely high calculations of MCH and MCHC, respectively.