3.8 Immunology Problem-Solving

Question 1

Which of the following serial dilutions contains an incorrect factor?

A. 1:4, 1:8, 1:16
B. 1:1, 1:2, 1:4
C. 1:5, 1:15, 1:45
D. 1:2, 1:6, 1:12

Answer 1

D. 1:2, 1:6, 1:12

Question 2

A patient was tested for syphilis by the RPR method and was reactive. A TP-PA test was performed and the result was negative. Subsequent testing showed the patient to have a high titer of ACAs by the ELISA method. Which routine laboratory test is most likely to be abnormal for this patient?

A. Activated partial thromboplastin time (APTT)
B. Anti–smooth muscle antibodies
C. Aspartate aminotransferase (AST)
D. C3 assay by immunonephelometry

Answer 2

A. Activated partial thromboplastin time (APTT)

Question 3

Inflammation involves a variety of biochemical and cellular mediators. Which of the following may be increased within 72 hours after an initial infection?

A. Neutrophils, macrophages, antibody, complement, α1-antitrypsin
B. Macrophages, T cells, antibody, haptoglobin, fibrinogen
C. Neutrophils, macrophages, complement, fibrinogen, C-reactive protein
D. Macrophages, T cells, B cells, ceruloplasmin, complement

Answer 3

C. Neutrophils, macrophages, complement, fibrinogen, C-reactive protein

Question 4

An 18-month-old boy has recurrent sinopulmonary infections and septicemia. Bruton thymidine kinase deficiency is suspected. Which test result would be markedly decreased?

A. Serum IgG, IgA, and IgM
B. Total T-cell count
C. Both B- and T-cell counts
D. Lymphocyte proliferation with phytohemagglutinin stimulation

Answer 4

A. Serum IgG, IgA, and IgM

Question 5

A patient received 5 units of FFP and developed a severe anaphylactic reaction. He has a history of respiratory and gastrointestinal infections. Post-transfusion studies showed all 5 units to be ABO compatible. What immunologic test would help to determine the cause of this transfusion reaction?

A. Complement levels, particularly C3 and C4
B. Flow cytometry for T-cell counts
C. Measurement of Igs
D. NBT test for phagocytic function

Answer 5

C. Measurement of Igs

Question 6

IFE revealed excessive amounts of polyclonal IgM and low concentrations of IgG and IgA. What is the most likely explanation of these findings and the best course of action?

A. Proper amounts of antisera were not added; repeat both tests
B. Test specimen was not added properly; repeat both procedures
C. Patient has common variable immunodeficiency; perform B-cell count
D. Patient has immunodeficiency with hyper-M; perform CD40 ligand (CD154) analysis

Answer 6

D. Patient has immunodeficiency with hyper-M; perform CD40 ligand (CD154) analysis

Question 7

SITUATION: A 54-year-old man was admitted to the hospital after having a seizure. Many laboratory tests were performed, including an RPR, but none of the results was positive. The physician suspects a case of late (tertiary) syphilis. Which test should be performed next?

A. Repeat RPR, followed by VDRL
B. Treponemal test, such as TP-PA on serum
C. VDRL on CSF
D. No laboratory test is positive for late (tertiary) syphilis

Answer 7

B. Treponemal test, such as TP-PA on serum

Question 8

A patient came to his physician complaining of a rash, severe headaches, stiff neck, and sleep problems. Laboratory tests of significance were an elevated sedimentation rate (ESR) and slightly increased liver enzymes. Further questioning of the patient revealed that he had returned from a hunting trip in upstate New York 4 weeks ago. His physician ordered a serological test for Lyme disease, and the assay was negative. What is the most likely explanation of these results?

A. The antibody response is not sufficient to be detected at this stage
B. The clinical symptoms and laboratory results are not characteristic of Lyme disease
C. The patient likely has early-stage HBV infection
D. Laboratory error has caused a false-negative result

Answer 8

A. The antibody response is not sufficient to be detected at this stage

Question 9

A 19-year-old girl came to her physician complaining of a sore throat and fatigue. Upon physical examination, lymphadenopathy was noted. Reactive lymphocytes were noted on the differential, but a rapid test for antibodies to IM was negative. Liver enzymes were only slightly elevated. What test(s) should be ordered next?

A. Hepatitis testing
B. EBV serological panel
C. HIV confirmatory testing
D. Bone marrow biopsy

Answer 9

B. EBV serological panel

Question 10

A patient received 2 units of RBCs following surgery. Two weeks after the surgery, the patient was seen by his physician and was found to have mild jaundice and slightly elevated liver enzymes. Hepatitis testing, however, was negative. What should be done next?

A. Nothing until more severe or definitive clinical signs develop
B. Repeat hepatitis testing immediately
C. Repeat hepatitis testing in a few weeks
D. Check blood bank donor records and contact donor(s) of transfused units

Answer 10

C. Repeat hepatitis testing in a few weeks

Question 11

A hospital employee received the final dose of the hepatitis B vaccine 3 weeks ago. She wants to donate blood. Which of the following results are expected from the hepatitis screen, and will she be allowed to donate blood?

A. HBsAg, positive; anti-HBc, negative—she may donate
B. HBsAg, negative; anti-HBc, positive—she may not donate
C. HBsAg, positive; anti-HBc, positive—she may not donate
D. HBsAg, negative; anti-HBc, negative—she may donate

Answer 11

D. HBsAg, negative; anti-HBc, negative—she may donate

Question 12

A pregnant woman came to her physician with a maculopapular rash on her face and neck. Her temperature was 37.7°C. Rubella tests for both IgG and IgM antibody were positive. What positive test(s) would reveal a diagnosis of congenital rubella syndrome in her baby after birth?

A. Positive rubella tests for both IgG and IgM antibody
B. Positive rubella test for IgM
C. Positive rubella test for IgG
D. No positive test is revealed in congenital rubella syndrome

Answer 12

B. Positive rubella test for IgM

Question 13

SITUATION: A patient with RA has acute pneumonia but a negative result on throat culture. The physician suspects an infection with Mycoplasma pneumoniae and requests an IgM-specific antibody test. The test is performed directly on serial dilutions of serum less than 4 hours old. The result is positive, giving a titer of 1:32. However, the test is repeated 3 weeks later, and the titer remains at 1:32. What test should be performed to determine if the patient is truly infected with M. pneumoniae?

A. IgG anti-M. pneumoniae
B. Cold agglutinins
C. M. pneumoniae PCR or other molecular assay
D. Respiratory culture

Answer 13

C. M. pneumoniae PCR or other molecular assay

Question 14

A patient had a PSA level of 60 ng/mL the day before surgery to remove a localized prostate tumor. One week after surgery, serum PSA was determined to be 8 ng/mL by the same method. What is the most likely cause of these results?

A. Incomplete removal of the malignancy
B. Cross reactivity of the antibody with another tumor antigen
C. Testing too soon after surgery
D. Hook effect with the PSA assay

Answer 14

C. Testing too soon after surgery

Question 15

A patient with symptoms associated with SLE and scleroderma was evaluated by immunofluorescence microscopy for ANAs by using the HEp-2 cell line as substrate. The cell line displayed a mixed pattern of fluorescence that could not be separated by serial dilutions of the serum. Which procedure would be most helpful in determining the antibody profile of this patient?

A. Use of a different tissue substrate
B. Absorption of the serum using the appropriate tissue extract
C. Requesting a new specimen
D. ELISA tests for specific antibodies

Answer 15

D. ELISA tests for specific antibodies

Question 16

A patient with joint swelling and pain tested negative for serum RF by both latex agglutination and ELISA methods. What other test would help establish a diagnosis of RA in this patient?

A. Anti-CCP
B. ANA testing
C. Flow cytometry
D. Complement levels

Answer 16

A. Anti-CCP

Question 17

What is the main advantage of the recovery and reinfusion of autologous stem cells?

A. It slows the rate of rejection of transplanted cells
B. It prevents graft-versus-host disease
C. No HLA testing is required
D. Engraftment occurs in a more efficient sequence

Answer 17

B. It prevents graft-versus-host disease

Question 18

A transplant recipient began to show signs of rejection 8 days after transplantation, and the organ was removed. What immune elements might be found in the rejected organ?

A. Antibody and complement
B. Primarily antibody
C. Macrophages
D. T cells

Answer 18

D. T cells

Question 19

A patient with ovarian cancer who has been treated with chemotherapy is being monitored for recurrence by using serum CA-125, CA-50, and CA 15–3. Six months after treatment the CA 15–3 is elevated, but the CA-125 and CA-50 remain low. What is the most likely explanation of these findings?

A. Ovarian malignancy has recurred
B. CA 15–3 is specific for breast cancer and indicates metastatic breast cancer
C. Testing error occurred in the measurement of CA 15–3 caused by poor analytical specificity
D. The CA 15–3 elevation is spurious and probably benign

Answer 19

A. Ovarian malignancy has recurred

Although CA-125 is the most commonly used tumor marker for ovarian cancer, not all ovarian tumors produce CA-125. Greatest sensitivity in monitoring for recurrence is achieved when several markers known to be increased in the malignant tissue type are measured simultaneously and when the markers are elevated (by malignancy) prior to treatment.

Question 20

An initial and repeat fourth-generation HIV screening test are both positive. The antibody differentiation assay is negative, as is the qualitative RNA PCR test. The patient shows no clinical signs of HIV infection, and the patient’s CD4 T-cell count is normal. Based on these results, which conclusion is correct?

A. Patient is diagnosed as HIV-1 positive
B. Patient is diagnosed as HIV-2 positive
C. Results are inconclusive
D. Patient is diagnosed as HIV-1 negative

Answer 20

D. Patient is diagnosed as HIV-1 negative

Question 21

A woman who has been pregnant for 12 weeks is tested for toxoplasmosis. Her IgM ELISA titer is 2.6 (reference range less than 1.6), and her IgG ELISA value is 66 (reference range less than 8). The physician asks you if these results indicated an infection during the past 12 weeks. Which of the following tests would you recommend to determine if the woman was infected during her pregnancy?

A. Toxoplasmosis PCR on amniotic fluid
B. Toxoplasmosis IgM on amniotic fluid
C. Toxoplasmosis IgG avidity
D. Amniotic fluid culture

Answer 21

C. Toxoplasmosis IgG avidity

Although IgM is positive, in toxoplasmosis, specific IgM may remain detectable for a year or more following infection. IgG avidity, or the strength of binding of a serum to the antigen of interest, is a useful method to determine if an infection is recent or in the distant past. IgG avidity will increase with time following an infection.

Question 22

On January 4, an SPE on a specimen obtained at your hospital in North Dakota from a 58-year-old patient shows a band at the β—γ junction. The specimen was also positive for RF. You recommend that an immunofixation test be performed to determine if the band represents a monoclonal Ig. Another specimen is obtained 2 weeks later by the physician in his office 30 miles away, and whole blood is submitted to you for IFE. The courier placed the whole blood specimen in an ice chest for transport. In this specimen, no β-γ band is seen in the serum protein lane, and the IgM lane is very faint. The RF on this specimen was negative. The physician wants to know what went wrong in your laboratory. Your response is:

A. Nothing went wrong in our laboratory; the patient had an infection 2 weeks ago, and it had cleared up
B. Something went wrong in our laboratory—we likely mislabeled one of the specimens; please resubmit a new specimen, and we will test it at no charge
C. We will run a second specimen after 2-mercaptoethanol treatment, which will eliminate IgM aggregates and allow for more sensitive monoclonal IgM detection
D. Please redraw another specimen from the patient, and this time, separate the serum from the clot in your office before placing the specimen on ice and sending it to us by courier

Answer 22

D. Please redraw another specimen from the patient, and this time, separate the serum from the clot in your office before placing the specimen on ice and sending it to us by courier

The most likely cause of the discrepant results is the presence of a type II cryoglobulin. This is a monoclonal RF. The protein likely precipitated during the courier ride and was, thus, in the clot when the laboratory separated the serum.

Question 23

A patient undergoing dialysis is positive for both HBsAg and anti-HBs. The physician suspects a laboratory error. Do you agree?

A. Yes; the patient should not test positive for both HBsAg and anti-HBs
B. No; incomplete dialysis of a patient in the core window phase of HBV infection will yield this result
C. No; it is likely the patient has recently received a hepatitis B booster vaccination within the past week, and this could have caused these results
D. Perhaps; a new specimen should be submitted to clear up the confusion

Answer 23

C. No; it is likely the patient has recently received a hepatitis B booster vaccination within the past week, and this could have caused these results

HBsAg will remain detectable at low levels following a vaccination for up to 1 to 2 weeks. Thus, patients who have received a second injection of hepatitis B vaccine may have anti-HBs and detectable antigen for a brief period. This has been reported more frequently in patients undergoing dialysis and in pediatric populations.

Question 24

You are evaluating an ELISA assay as a replacement for your IFA ANA test. You test 50 specimens in duplicate on each assay. The ELISA assay uses a HEp-2 extract as its antigen source. The correlation between the ELISA and IFA tests is only 60% (30 of 50 specimens agree). Which of the following is the next best course of action?

A. Test another 50 specimens
B. Perform a competency check on the medical laboratory scientists who performed the tests
C. Order a new lot of both kits and then retest on the new lots
D. Refer the discrepant specimens for testing by another method

Answer 24

D. Refer the discrepant specimens for testing by another method