Case Studies

Question 1

1. A 13-year-old male had numerous absences from school in the spring because of cold symptoms that included head congestion and cough. He had received antibiotic treatment twice, but he seemed to get one cold after another. A complete blood count (CBC) showed no overall increase in WBCs, but a mild eosinophilia was present. Because he had no fever or other signs of infection, his physician suggested that allergy testing be run.

a. What would account for the eosinophilia noted?

Answer 1

a. An increase in eosinophils is typically found in allergic individuals. Interleukins released by stimulated Th1 cells are involved in the recruitment of eosinophils from the bone marrow. Although there are other causes of eosinophilia, such as a parasitic infection, an increased number most often indicates an allergic reaction.

Question 2

1. A 13-year-old male had numerous absences from school in the spring because of cold symptoms that included head congestion and cough. He had received antibiotic treatment twice, but he seemed to get one cold after another. A complete blood count (CBC) showed no overall increase in WBCs, but a mild eosinophilia was present. Because he had no fever or other signs of infection, his physician suggested that allergy testing be run.

b. What tests should be run for this patient?

Answer 2

b. The patient can have a skin prick test performed to determine which allergens he is sensitized to. The patient would know his results immediately because a positive test would be indicated by formation of wheal-and flare reactions within 20 minutes at the site(s) of injection. If he is unable to discontinue any antihistamines he might be taking, or if a clear area of skin in his forearm or back could not be found, a solid-phase immunoassay for allergen-specific IgE could be performed.

Question 3

1. A 13-year-old male had numerous absences from school in the spring because of cold symptoms that included head congestion and cough. He had received antibiotic treatment twice, but he seemed to get one cold after another. A complete blood count (CBC) showed no overall increase in WBCs, but a mild eosinophilia was present. Because he had no fever or other signs of infection, his physician suggested that allergy testing be run.

c. If the patient was treated with allergy immunotherapy, what test could be used to monitor his response over time?

Answer 3

c. A solid-phase immunoassay for total IgE could be performed to monitor the patient’s response to allergen immunotherapy. If the therapy is successful, the IgE concentration in the patient’s serum should decrease to a level within the reference age for patients his age.

Question 4

2. A 55-year-old male went to his physician complaining of feeling tired and run down. Two months previously, he had pneumonia and was concerned that he might not have completely recovered. He indicated that his symptoms only become noticeable if he goes out in the cold.
   A CBC count was performed, showing that his WBC count was within normal limits; however, his RBC count was just below normal. A DAT performed on RBCs was weakly positive after incubating at room temperature for 5 minutes. When the DAT was repeated with monospecific reagents, the tube with anti-C3d was the only one positive.

a. What does a positive DAT indicate?

Answer 4

a. A positive DAT indicates that the red blood cells (RBCs) are coated with either antibody or complement components. The destruction of some RBCs is the reason for the man’s symptoms.

Question 5

2. A 55-year-old male went to his physician complaining of feeling tired and run down. Two months previously, he had pneumonia and was concerned that he might not have completely recovered. He indicated that his symptoms only become noticeable if he goes out in the cold.
   A CBC count was performed, showing that his WBC count was within normal limits; however, his RBC count was just below normal. A DAT performed on RBCs was weakly positive after incubating at room temperature for 5 minutes. When the DAT was repeated with monospecific reagents, the tube with anti-C3d was the only one positive.

b. What is the most likely class of the antibody causing the reaction?

Answer 5

b. The most likely cause of the positive DAT is the presence of an antibody of the IgM class. It might be an anti-I, triggered by Mycoplasma pneumonia. This is a cold-reacting antibody.

Question 6

2. A 55-year-old male went to his physician complaining of feeling tired and run down. Two months previously, he had pneumonia and was concerned that he might not have completely recovered. He indicated that his symptoms only become noticeable if he goes out in the cold.
   A CBC count was performed, showing that his WBC count was within normal limits; however, his RBC count was just below normal. A DAT performed on RBCs was weakly positive after incubating at room temperature for 5 minutes. When the DAT was repeated with monospecific reagents, the tube with anti-C3d was the only one positive.

c. Why was the DAT positive only with anti-C3d when monospecific reagents were used?

Answer 6

c. A DAT that is only positive with anti-C3d indicates that only complement products are present on the RBCs. This is a further indication that the antibody is an IgM antibody because it does not remain on the cells at 37°C but does trigger complement activation, which can cause the cell destruction.