Block B - Testing for Pregnancy Flashcards
What is the key hormone detected in modern pregnancy tests?
A) Estrogen
B) Progesterone
C) hCG
D) Luteinizing Hormone (LH)
C, hCG
Which pregnancy test method involves latex beads coated with hCG?
A) Radioimmunoassay (RIA)
B) Inhibition of Latex Agglutination (ILA)
C) Dip-stick test
D) ELISA
B
Why was the rabbit test for pregnancy unreliable?
A) It was slow and required killing the animal
B) It did not detect hCG
C) It had a high false-positive rate
D) It could only detect late pregnancy
A
What is the advantage of radioimmunoassay (RIA) over latex agglutination for pregnancy testing?
A) RIA is quantitative and highly sensitive
B) RIA does not require antibodies
C) RIA is cheaper and faster
D) RIA is a non-immunoassay method
A
Why do dip-stick pregnancy tests have two lines?
A) One line detects hCG, the other is a control
B) One line confirms fertilization, the other confirms implantation
C) The first line detects progesterone, the second detects hCG
D) One line appears only in early pregnancy
A
Which type of immune cells does HIV primarily infect?
A) CD8+ T cells
B) B cells
C) CD4+ T cells
D) Macrophages
C
What is the purpose of flow cytometry in HIV monitoring?
A) To detect viral RNA
B) To quantify CD4+ T cell counts
C) To measure hCG levels
D) To diagnose acute infections
B
What does side scatter (SS) in flow cytometry measure?
A) Cell size
B) Cell complexity and granularity
C) Cell fluorescence
D) Cell density
B
What is the key marker for T-helper cells in flow cytometry?
A) CD3+
B) CD8+
C) CD4+
D) CD19+
C
Why is flow cytometry preferred over fluorescent microscopy for HIV monitoring?
A) It is faster and more automated
B) It detects HIV viral proteins
C) It can detect cytokines
D) It requires fewer samples
A
What is the main difference between RIST and RAST tests for allergy?
A) RIST detects total IgE, RAST detects specific IgE
B) RIST is qualitative, RAST is quantitative
C) RIST detects allergens, RAST detects antibodies
D) RIST is more sensitive than RAST
A
What type of immunoassay is used in RAST tests?
A) Fluorescent Polarization Immunoassay (FPIA)
B) Radioimmunoassay (RIA)
C) Latex Agglutination Test
D) Dip-stick test
B
What happens in passive cutaneous anaphylaxis when an allergic reaction occurs?
A) IgG binds to allergens and activates mast cells
B) IgE binds to mast cells, causing histamine release
C) T cells attack allergens
D) B cells produce cytokines
B
What is the main principle of Fluorescence Polarization Immunoassay (FPIA)?
A) Fluorescent-labeled drugs rotate freely when unbound
B) Antigens and antibodies react to produce agglutination
C) Radioactive hCG binds to antibodies
D) Cell size and granularity are measured
A
Which of the following drugs is commonly monitored using FPIA?
A) hCG
B) Digoxin
C) Insulin
D) Estrogen
B
What are the three main types of pregnancy immunoassays?
-Inhibition of Latex Agglutination (ILA) – clinical use
-Radioimmunoassay (RIA) – highly sensitive, uses radioactivity
-Dip-stick (Lateral Flow Assay) – home & clinical, visual detection
How does a dip-stick pregnancy test work? (3 marks)
-Anti-hCG antibodies on latex beads bind hCG in urine.
-The beads travel up the filter and bind immobilized anti-hCG, forming a colored line.
-A second line binds anti-rabbit IgG as a control.
What does flow cytometry measure in HIV patients? (3 marks)
-CD4+ T cell counts – key for tracking HIV progression.
-Forward scatter (FS) – cell size.
-Side scatter (SS) – granularity & complexity.
How do RIST and RAST tests differ?
RIST = Measures total IgE (overall allergy response).
RAST = Measures specific IgE (identifies allergens)
What principle does Fluorescence Polarization Immunoassay (FPIA) use? (3 marks)
-Measures drug concentration in serum.
-High drug levels = More unbound drug → low fluorescence polarization.
-Low drug levels = More bound drug → high fluorescence polarization.
Why is FPIA preferred over ELISA for therapeutic drug monitoring?
A) FPIA is homogeneous, eliminating the need for separation steps.
B) ELISA requires more patient blood volume for testing.
C) ELISA is less specific than FPIA for small molecules.
D) FPIA can measure large and small molecules equally well.
A because FPIA is faster and requires fewer wash steps than ELISA because it does not require antigen immobilization.
A patient on digoxin therapy has low blood digoxin levels despite taking their prescribed dose. What could explain this?
A) The patient is metabolizing digoxin too quickly due to drug interactions.
B) The test is detecting a different cardiac glycoside, giving a false result.
C) The patient has developed antibodies against digoxin, making it undetectable.
D) The digoxin assay is not sensitive enough to measure therapeutic levels.
A, Rifampin and St. John’s Wort increase digoxin metabolism, lowering levels.
Why does Fluorescence Polarization Immunoassay (FPIA) work best for small molecules like drugs?
A) Small molecules rotate more freely in solution, affecting fluorescence polarization.
B) Large molecules absorb too much light, interfering with detection.
C) Large molecules bind antibodies too strongly, preventing accurate competition.
D) Small molecules fluoresce more efficiently than larger ones.
A, The degree of rotation of a fluorescently labeled molecule depends on its size. More rotation = lower polarization.
Why might immunotherapy (allergy shots) shift antibody production from IgE to IgG?
A) Repeated exposure to the allergen promotes IgG4 production, which blocks mast cell activation.
B) IgG is more stable in the blood, so it outcompetes IgE.
C) IgG directly destroys allergens through complement activation.
D) The therapy suppresses the immune system, reducing IgE production.
A, IgG4 acts as a “blocking antibody” that prevents allergens from cross-linking IgE on mast cells, reducing allergic responses.
A patient has high total IgE levels but negative RAST results for all tested allergens. What does this suggest?
A) The patient may have a non-allergic condition that elevates IgE, like parasitic infection.
B) The test was performed incorrectly and should be repeated.
C) The patient has a very mild allergy that is undetectable by current tests.
D) The patient has an autoimmune disease affecting IgE production.
A, Parasitic infections (e.g., helminths) and chronic diseases (e.g., hyper-IgE syndrome) can elevate total IgE without an allergic reaction.
In flow cytometry, why is it important to use multiple fluorescent markers when analyzing immune cells?
A) It allows identification of distinct immune cell subsets based on surface markers.
B) It increases the total fluorescence detected, improving accuracy.
C) It prevents antibody cross-reactivity and non-specific binding.
D) It improves light scattering and reduces autofluorescence.
A, CD3+CD4+ identifies helper T cells, CD3+CD8+ identifies cytotoxic T cells.
A patient with suspected HIV infection has a normal CD4+ T cell count but tests positive for viral RNA. What is a possible explanation?
A) The patient is in the acute stage of HIV infection before significant CD4+ depletion.
B) The patient has a CD4 mutation that makes their cells resistant to HIV.
C) The flow cytometry results are incorrect, and the test should be repeated.
D) The viral RNA test is detecting an unrelated virus.
A, Acute HIV (seroconversion phase) often shows high viral load but no CD4 drop yet.
Could a dip-stick pregnancy test work if an hCG mutant was produced that lacked the beta-subunit? Why or why not?
A) No, because current tests target the unique beta-subunit of hCG.
B) Yes, because the alpha-subunit is still recognized by antibodies.
C) No, because the mutant hCG would not be present in urine.
D) Yes, because any form of hCG will bind to anti-hCG antibodies.
A, The alpha-subunit of hCG is shared with LH, FSH, and TSH, so pregnancy tests target β-hCG for specificity.
Why do some pregnancy tests produce false positives in women with trophoblastic diseases or certain cancers?
A) Cancer cells can produce hCG or structurally similar molecules.
B) The immune system reacts to cancer by producing antibodies that mimic hCG.
C) These conditions interfere with the colorimetric reaction in dip-stick tests.
D) The test detects progesterone instead of hCG.
A, Choriocarcinoma, testicular cancer, and molar pregnancies can elevate hCG.
A woman takes a home pregnancy test, and the test line appears faint. What could explain this?
A) She is very early in pregnancy and has low hCG levels.
B) The test is defective and should be discarded.
C) The woman is not pregnant, but the test is reacting to progesterone.
D) The test is an antigen-based assay and should be repeated using RIA.
A, A faint line can also occur due to diluted urine (low concentration of hCG) or an evaporation line.
Which of the following historical pregnancy tests involved injecting urine into immature mice or rats?
A) Frog test
B) A-Z test (Aschheim-Zondek test)
C) Hemagglutination inhibition test
D) Radioimmunoassay
B) A-Z test (Aschheim-Zondek test)
Which pregnancy test method is used in home pregnancy kits?
A) Radioimmunoassay
B) Inhibition of latex agglutination
C) Dip-stick lateral flow assay
D) ELISA
C) Dip-stick lateral flow assay
What is a limitation of Radioimmunoassay (RIA) for pregnancy testing?
A) It cannot be automated.
B) It has low sensitivity.
C) It produces radioactive waste.
D) It is slower than traditional biological assays.
C) It produces radioactive waste.
What is the primary advantage of digital pregnancy tests over traditional dip-stick tests?
A) They do not rely on immunoassays.
B) They detect progesterone instead of hCG.
C) They use a spectrophotometer to quantify hCG concentration.
D) They require laboratory analysis.
C) They use a spectrophotometer to quantify hCG concentration.
Which immune cell population is monitored using flow cytometry to track HIV progression?
A) CD8+ T cells
B) B cells
C) CD4+ T cells
D) Natural Killer (NK) cells
C) CD4+ T cells
What does forward scatter (FS) in flow cytometry indicate?
A) Cell granularity
B) Cell size
C) Cell fluorescence
D) Antibody concentration
B) Cell size
Which marker is used to differentiate helper T cells from other T cells in flow cytometry?
A) CD3
B) CD8
C) CD4
D) CD19
C) CD4
What is the major limitation of fluorescence microscopy compared to flow cytometry in HIV monitoring?
A) It requires expensive lasers.
B) It can only count a small number of cells and is operator-dependent.
C) It cannot detect HIV infection.
D) It cannot be used to quantify T cell subsets.
B) It can only count a small number of cells and is operator-dependent.
What does RIST (Radioimmunosorbent Test) measure?
A) Total IgE levels
B) Specific IgE to allergens
C) Total IgG levels
D) Histamine concentration
A) Total IgE levels
What is a major limitation of RIST compared to RAST?
A) It is more expensive.
B) It only provides total IgE levels, not allergen-specific IgE.
C) It requires live animals for testing.
D) It cannot be used for industrial allergy screening.
B) It only provides total IgE levels, not allergen-specific IgE.
What is the primary advantage of cytometric bead arrays (CBAs) over traditional RAST for allergy testing?
A) CBAs use fluorescent beads instead of radioactivity.
B) CBAs detect total IgE only.
C) CBAs require larger sample volumes.
D) CBAs have lower sensitivity.
A) CBAs use fluorescent beads instead of radioactivity.
What is the principle of Fluorescence Polarization Immunoassay (FPIA)?
A) Large fluorescent molecules rotate faster than small molecules.
B) Small fluorescent molecules rotate faster than large molecules.
C) Fluorescence is absorbed by unbound drug molecules.
D) Polarization is increased when the drug is free in solution.
B) Small fluorescent molecules rotate faster than large molecules.
Why is FPIA preferred for small molecules like drugs?
A) It is a competitive immunoassay.
B) Small molecules fluoresce more efficiently.
C) Large molecules do not rotate freely, making polarization effects unreliable.
D) It only works for molecules over 50,000 Da.
C) Large molecules do not rotate freely, making polarization effects unreliable.
Describe the three immunoassay-based pregnancy tests and explain their advantages/disadvantages.
-Inhibition of Latex Agglutination (ILA) → Clinical use, qualitative, time-consuming.
-Radioimmunoassay (RIA) → Clinical, quantitative, highly sensitive, but radioactive waste.
-Dip-stick lateral flow assay → Home & clinical, fast, easy, but not quantitative.
Why might a pregnancy test be positive in a non-pregnant individual? (3 marks)
Ectopic pregnancy
Trophoblastic tumors (e.g., choriocarcinoma)
Incomplete miscarriage
Explain how flow cytometry is used to monitor HIV progression. (3 marks)
-CD4+ T cell enumeration
-Fluorescent antibodies against CD3/CD4
-Stages of HIV progression (Acute, Chronic, AIDS)
What is the significance of a low CD4/CD8 ratio in HIV patients? (3 marks)
-A low ratio suggests immune suppression
-Indicates progression toward AIDS
-Can be used to track ART (antiretroviral therapy) effectiveness
Compare and contrast RIST vs. RAST in allergy testing. (3 marks)
RIST = Measures total IgE, good for diagnosing atopy but not specific allergens.
RAST = Measures specific IgE, used for identifying allergens.
What are the advantages of fluorescent bead arrays over RAST? (3 marks)
-Detect multiple allergens at once
-No radioactivity required
-Higher sensitivity & specificity
Explain why FPIA is better suited for drug monitoring than ELISA. (3 marks)
-Faster & requires no wash steps
-Homogeneous assay (no separation needed)
-High sensitivity for small drugs like digoxin
A patient with suspected ectopic pregnancy tests negative on a home pregnancy test but has mildly elevated hCG in a clinical blood test. What is the most likely explanation?
A) The dip-stick test is faulty and should be discarded.
B) The patient’s urine hCG levels are too low for detection.
C) The patient has an undetectable pregnancy due to rapid metabolism of hCG.
D) The presence of heterophile antibodies interfered with the dip-stick assay.
B) The patient’s urine hCG levels are too low for detection.
Which of the following would NOT cause a false-positive result in an hCG-based pregnancy test?
A) Trophoblastic tumors (e.g., choriocarcinoma)
B) Excess luteinizing hormone (LH) production
C) Recent miscarriage
D) High progesterone levels due to ovarian cysts
D) High progesterone levels due to ovarian cysts.
What is a major flaw in traditional hemagglutination inhibition pregnancy tests?
A) They are highly sensitive but slow.
B) They cannot differentiate hCG from LH.
C) They require radioactive labeling.
D) They use monoclonal antibodies, which lower specificity.
B) They cannot differentiate hCG from LH.
A patient undergoing antiretroviral therapy (ART) has a stable CD4+ count but a worsening CD4/CD8 ratio. What does this indicate?
A) The treatment is effective, and the patient is recovering.
B) CD8+ T cells are increasing, suggesting immune activation or co-infection.
C) Flow cytometry results are unreliable in HIV patients.
D) The patient’s CD4+ T cells are being replaced by B cells.
B) CD8+ T cells are increasing, suggesting immune activation or co-infection.
Why is flow cytometry preferred over ELISA for tracking HIV progression?
A) ELISA cannot quantify absolute CD4+ T cell counts.
B) Flow cytometry detects HIV RNA, while ELISA does not.
C) Flow cytometry is cheaper and requires less expertise than ELISA.
D) ELISA is used for antibody detection, which is not useful for monitoring disease progression.
A) ELISA cannot quantify absolute CD4+ T cell counts.
Which of the following would most likely compromise the accuracy of a CD4+ T cell count measured via flow cytometry?
A) Use of fluorochrome-labeled monoclonal antibodies
B) Improper gating strategy leading to inclusion of non-CD4+ lymphocytes
C) Low side scatter (SSC) settings, increasing cell granularity detection
D) Use of forward scatter (FSC) to exclude non-lymphoid cells
B) Improper gating strategy leading to inclusion of non-CD4+ lymphocytes.
A patient with high total IgE (RIST test positive) but negative RAST results for all allergens likely has:
A) A parasitic infection or a non-allergic cause of IgE elevation.
B) Severe anaphylaxis to an unidentified allergen.
C) A RAST test error requiring repeat testing.
D) A local allergic response that is only detectable in skin tests.
A) A parasitic infection or a non-allergic cause of IgE elevation.
What is a major advantage of cytometric bead arrays (CBAs) over traditional RAST tests in allergy diagnosis?
A) CBAs measure multiple allergens simultaneously using fluorescence-based detection.
B) CBAs detect total IgE levels, while RAST does not.
C) CBAs require radioactive labeling for increased sensitivity.
D) CBAs are less sensitive than RAST but more specific.
A) CBAs measure multiple allergens simultaneously using fluorescence-based detection.
Which of the following could cause a false negative in an allergy skin prick test?
A) Patient has high circulating IgE levels.
B) Patient is taking antihistamines.
C) Test was performed on the forearm instead of the back.
D) Patient has an autoimmune condition.
B) Patient is taking antihistamines.
Why is FPIA best suited for monitoring small molecule drugs like digoxin?
A) Small molecules rotate freely in solution, affecting fluorescence polarization.
B) Large molecules have higher fluorescence intensity, making them difficult to detect.
C) Large molecules outcompete the fluorescent-labeled drug, reducing accuracy.
D) FPIA requires a high molecular weight antigen for proper function.
A) Small molecules rotate freely in solution, affecting fluorescence polarization.
A patient taking biotin supplements shows abnormally low thyroid hormone levels in an ELISA-based TSH assay. What is the most likely explanation?
A) Biotin interferes with streptavidin-biotin capture systems used in sandwich ELISA.
B) Biotin directly inhibits TSH production in the thyroid.
C) Biotin causes cross-reactivity between TSH and hCG.
D) The patient’s actual TSH levels are too high for detection.
A) Biotin interferes with streptavidin-biotin capture systems used in sandwich ELISA.
A patient presents with symptoms of pregnancy, but repeated dip-stick tests are negative. A quantitative ELISA for hCG shows a value of 5 mIU/mL, just at the detection threshold for pregnancy. What would you recommend next?
A) Perform a radioimmunoassay (RIA) to confirm the result.
B) Repeat the dip-stick test with a different brand.
C) Wait 48 hours and repeat the quantitative hCG test.
D) Test for progesterone levels, as hCG is unreliable.
C) Wait 48 hours and repeat the quantitative hCG test.
A patient with advanced HIV infection has a low CD4+ count as measured by flow cytometry, but an unusually high total lymphocyte count. The clinician suspects an error in the gating strategy. What could explain this discrepancy?
A) The forward scatter (FS) setting was too high, excluding some CD4+ T cells.
B) The side scatter (SS) setting mistakenly included granulocytes, inflating total lymphocyte counts.
C) There was nonspecific antibody binding, leading to false detection of CD4+ cells.
D) The sample contained dead or apoptotic cells, artificially lowering CD4+ counts.
D) The sample contained dead or apoptotic cells, artificially lowering CD4+ counts.
A flow cytometry analysis of an HIV-positive patient shows unexpectedly high CD4/CD8 ratio, even though the patient has worsening symptoms. What is the best course of action?
A) Perform a repeat flow cytometry test with a fresh blood sample.
B) Confirm HIV progression using a plasma viral load (HIV RNA PCR) test.
C) Assume the patient has recovered and stop ART (antiretroviral therapy).
D) Perform a Western blot to confirm HIV status.
B) Confirm HIV progression using a plasma viral load (HIV RNA PCR) test.
A patient with a history of severe allergic reactions undergoes RAST testing for specific IgE antibodies to various allergens. All tests return negative, yet the patient continues to experience anaphylaxis upon peanut exposure. What is the most likely explanation?
A) The patient has a non-IgE mediated allergy (e.g., food protein-induced enterocolitis syndrome).
B) The RAST test was performed incorrectly and should be repeated.
C) The patient is not allergic, and their symptoms are due to psychosomatic factors.
D) The RAST test had too low sensitivity to detect IgE at clinically relevant levels.
A) The patient has a non-IgE mediated allergy (e.g., food protein-induced enterocolitis syndrome).
A company develops a new microarray-based allergy test that detects hundreds of allergens in a single assay. However, it shows higher false-positive rates than traditional RAST. What could explain this?
A) The test uses fluorescent beads, which are less accurate than radioimmunoassays.
B) The increased sensitivity of microarrays picks up low-affinity IgE, which may not be clinically relevant.
C) The test cannot differentiate IgG from IgE, leading to cross-reactivity.
D) The test requires larger blood samples, which increases errors.
B) The increased sensitivity of microarrays picks up low-affinity IgE, which may not be clinically relevant.
A patient on digoxin therapy has normal blood drug levels when measured by FPIA, yet they exhibit signs of digoxin toxicity (nausea, arrhythmias). What could be causing this?
A) The patient has anti-digoxin antibodies, which interfere with FPIA detection.
B) The patient’s kidney function has improved, causing drug accumulation.
C) The patient is metabolizing digoxin too quickly.
D) The FPIA method underestimates digoxin concentrations due to low drug polarity.
A) The patient has anti-digoxin antibodies, which interfere with FPIA detection.
A hospital laboratory finds inconsistent results between ELISA-based and fluorescence polarization immunoassay (FPIA) for therapeutic drug monitoring of theophylline. What is the most likely reason?
A) FPIA is a competitive assay, while ELISA is a sandwich assay, leading to different sensitivities.
B) ELISA requires radioactive labels, which degrade over time.
C) FPIA is more affected by sample viscosity, altering drug-antibody binding.
D) ELISA has higher fluorescence interference, leading to overestimation of drug levels.
A) FPIA is a competitive assay, while ELISA is a sandwich assay, leading to different sensitivities.
What is the primary reason why home dip-stick pregnancy tests use monoclonal antibodies?
A) Monoclonal antibodies provide higher specificity for detecting hCG.
B) Monoclonal antibodies allow for cross-reactivity with LH and FSH.
C) Polyclonal antibodies are too expensive to use in home pregnancy tests.
D) Monoclonal antibodies react better with progesterone than polyclonal antibodies.
A) Monoclonal antibodies provide higher specificity for detecting hCG, targeting specific epitopes of hCG, reducing false positives from LH or FSH.
Which immunoassay method for pregnancy testing is most appropriate for clinical use when a precise hCG concentration is required?
A) Dip-stick lateral flow assay
B) Inhibition of latex agglutination test
C) Radioimmunoassay (RIA)
D) Wine-mixing test
C) Radioimmunoassay (RIA)
What is a major disadvantage of inhibition of latex agglutination tests for pregnancy detection?
A) They require radiolabeled antibodies.
B) They are time-consuming and depend on visual interpretation.
C) They are only useful for detecting progesterone.
D) They produce high levels of false positives.
B) They are time-consuming and depend on visual interpretation.
Flow cytometry is commonly used to monitor HIV progression by tracking:
A) Viral RNA load in the bloodstream
B) CD4+ T cell counts in blood samples
C) Anti-HIV antibody levels
D) Cytokine production by macrophages
B) CD4+ T cell counts in blood samples.
Which factor can interfere with the accuracy of CD4+ T cell enumeration in flow cytometry?
A) Using monoclonal antibodies specific for CD8+ instead of CD4+
B) Incorrect gating of lymphocyte populations
C) Use of fluorochromes with high quantum yield
D) Performing flow cytometry on plasma instead of whole blood
B) Incorrect gating of lymphocyte populations.
A hospital lab finds that CD4+ T cell counts are consistently lower than expected in patients undergoing HIV treatment. Which of the following is the most likely cause of error?
A) Overestimation of CD8+ T cells due to poor antibody specificity
B) Use of old blood samples, leading to cell degradation
C) Incorrectly adjusting forward scatter (FS) settings
D) Using too many fluorescent labels, leading to signal quenching
B) Use of old blood samples, leading to cell degradation.
A patient undergoes RIST and RAST testing. Their RIST result is high, but all RAST tests for specific allergens are negative. What is the most likely interpretation?
A) The patient has an autoimmune disease.
B) The patient has elevated total IgE but no specific IgE for common allergens.
C) The RIST test was performed incorrectly.
D) The patient is not allergic and should undergo immunotherapy.
B) The patient has elevated total IgE but no specific IgE for common allergens.
What is the main advantage of cytometric bead arrays (CBAs) over traditional RAST tests?
A) CBAs can detect multiple allergens simultaneously.
B) CBAs require fewer antibodies for allergen detection.
C) CBAs do not require fluorescent labeling.
D) CBAs can directly quantify total IgE levels.
A) CBAs can detect multiple allergens simultaneously.
Why is fluorescence polarization immunoassay (FPIA) particularly useful for monitoring small molecule drugs like digoxin?
A) It does not require washing steps, making it fast and efficient.
B) It works only for large proteins, making it highly specific.
C) It does not rely on competitive binding assays.
D) It detects fluorescently labeled drugs bound to albumin.
A) It does not require washing steps, making it fast and efficient.
A hospital uses ELISA for monitoring theophylline levels, but results show high variability. Why might FPIA be a better alternative?
A) FPIA is less sensitive, reducing false positives.
B) FPIA has faster turnaround time and is automated.
C) ELISA is only suitable for hormone detection.
D) ELISA does not work with competitive binding assays.
B) FPIA has faster turnaround time and is automated.
A patient on digoxin therapy has normal blood drug levels by FPIA, yet shows signs of toxicity (arrhythmias, nausea). What is the most likely explanation?
A) The patient has kidney failure, leading to drug accumulation.
B) The patient’s digoxin metabolites interfere with FPIA results.
C) The FPIA test was contaminated.
D) The digoxin antibody used in FPIA is too sensitive, causing false negatives.
B) The patient’s digoxin metabolites interfere with FPIA results.
