8 IMMUNOLOGY PROBLEM-SOLVING Flashcards
(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
D. 1:2, 1:6, 1:12
All the dilutions are multiplied by the same factor in a progression except the last one: 1:2 to 1:6 is × 3, whereas 1:6 to 1:12 is × 2. Threefold dilutions of a 1:2 dilution would result in a 1:6 followed by a 1:18.
(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
A. Activated partial thromboplastin time (APTT)
Approximately 50% to 70% of patients with ACAs also have the lupus anticoagulant (LAC) in their serum. LAC is an Ig that interferes with in vitro coagulation tests: prothrombin time (PT), APTT, and dilute Russell viper venom (DRVV) time. These tests require phospholipid for the activation of factor X. About 30% of patients with antibodies to cardiolipin or phospholipids have a biological false-positive RPR result. Anti–smooth muscle is most commonly associated with chronic active hepatitis, and increased AST with necrotic liver diseases. Although ACA and LAC may be associated with SLE, the majority of patients with these antibodies do not have SLE and would have a normal C3 level.
(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
C. Neutrophils, macrophages, complement, fibrinogen, C-reactive protein
The correct list, in which all mediators are involved in an inflammatory response within 72 hours after initial infection, is neutrophils, macrophages, complement, fibrinogen, and C-reactive protein. Phagocytic cells, acute phase reactants, and fibrinolytic factors enter the site of inflammation. Antibody and lymphocytes do not enter until later.
(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
A. Serum IgG, IgA, and IgM
The patient with Bruton thymidine kinase deficiency presents with clinical symptoms related to recurrent infections, demonstrated in the laboratory by decreased or absent Igs. Peripheral blood B cells are absent or markedly reduced, but T cells are normal in number and function. Because phytohemagglutinin is a T-cell mitogen, the lymphocyte proliferation test using PHA would be normal for this patient.
(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
C. Measurement of Igs
The patient had an anaphylactic reaction to a plasma product. This, combined with the history of respiratory and gastrointestinal infections, suggests a selective IgA deficiency. Measurement of Igs would be helpful in this case. A low serum IgA and normal IgG substantiate the diagnosis of selective IgA deficiency. Such patients frequently produce anti-IgA, which is often responsible for a severe transfusion reaction when ABO-compatible plasma is administered.
(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
Low plasma concentrations of IgG and IgA and an abundance of IgM is consistent with the CD40 ligand deficiency. Most cases are X-linked and result from a mutation of the gene TNFSF5, which encodes a receptor needed for switching Ig production. Patients with common variable immunodeficiency have low serum IgG, IgA, and IgM.
(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
B. Treponemal test, such as TP-PA on serum
Serum antibody tests, such as RPR and VDRL, are often negative in cases of late syphilis. However, treponemal tests remain positive in greater than 95% of cases. The VDRL test on CSF is the most specific test for diagnosis of neurosyphilis because treponemal test results remain positive after treatment. It should be used as the confirmatory test when the serum treponemal test result is positive. However, the CSF VDRL is limited in sensitivity and would not be positive if the serum treponemal-specific antibody test was negative.
(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
A. The antibody response is not sufficient to be detected at this stage
The antibody response to B. burgdorferi may not develop until several weeks after initial infection. The antibody test should be repeated 2 to 4 weeks later. To confirm a positive EIA, samples that initially test positive or equivocal (indeterminate) should be retested using a second enzyme immunoassay or immunoblot method. Regardless of the laboratory results, if the physician suspects Lyme disease, treatment should begin immediately.
(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
B. EBV serological panel
An EBV serological panel would give a more accurate assessment than a rapid slide IM test. The time of appearance of the various antibodies to the viral antigens differs according to the clinical course of the infection.
(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
C. Repeat hepatitis testing in a few weeks
The level of HBsAg may not have reached detectable levels, and antibodies to HBc and HCV would not have yet developed. Waiting 1 or 2 weeks and repeating the test may reveal evidence of hepatitis virus infection.
(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
D. HBsAg, negative; anti-HBc, negative—she may donate
She may donate if she is symptom free. The response to hepatitis B vaccine would include a positive result for anti-HBs, a test not normally a part of routine donor testing. She will be negative for HBsAg and anti-HBc; however, transient antigen positivity (less than 2 weeks) may be seen following vaccination.
(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
B. Positive rubella test for IgM
A finding of IgG is not definitive for congenital rubella syndrome because IgG crosses the placenta from the mother; however, demonstration of IgM, even in a single neonatal sample, is diagnostic.
(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
C. M. pneumoniae PCR or other molecular assay
The IgM-specific antibody test for M. pneumoniae detects antibodies to mycoplasmal membrane antigens and, unlike cold agglutinins, is specific for M. pneumoniae. A positive result (titer of 1:32 or higher) occurs during the acute phase in about 87% of M. pneumoniae infections and does not need to be confirmed by assay of convalescent serum. However, Mycoplasma IgM may last a year or more, thus its presence does not always indicate a current infection. PCR performed on a respiratory specimen is the definitive test and should be performed if there is a question about an IgM result.
(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
(14) When monitoring the level of a tumor marker for treatment efficacy or recurrence, the half-life of the protein must be considered when determining the testing interval. PSA has a half-life of almost 4 days and would not reach normal levels after surgery for approximately 3 to 4 weeks. The hook effect is the result of very high antigen levels giving a lower than expected result in a double antibody sandwich assay when both antibodies and sample are added at the same time.
(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
D. ELISA tests for specific antibodies
Many patients with multiorgan autoimmune disease display symptoms that overlap two or more diseases and have complex mixtures of serum autoantibodies. The HEp-2 substrate is the most sensitive cell line for immunofluorescent microscopy because it contains cells in various mitotic stages, which exposes the serum to more antigens. Use of a nonhuman substrate, such as Crithidia, may help identify dsDNA antibodies but would not aid in differentiating all of the antibodies in a complex mixture. The best methods are ELISA, line blots, and multiplex tests because they are more specific than immunofluorescence microscopy for identifying antibodies to specific antigens. These assays are often used to measure antibodies to ENAs, which may be partially or completely lost during fixation of cells used for immunofluorescent microscopy. These antibodies cause a speckled pattern and are seen in a wide range of autoimmune diseases. Identification of the anti-ENA specificities is helpful in differentiating these diseases.
