A 34-year-old man who injects drugs has known chronic hepatitis B, with HBsAg reactive for 6 years and a normal ALT at his last visit a year ago. He now has jaundice and malaise. Results: ALT 1,650 U/L (reference < 40 U/L); HBsAg reactive; IgM anti-HBc nonreactive; total anti-HBc reactive; HBeAg nonreactive; anti-HBe reactive; HBV DNA 900 IU/mL (1,200 IU/mL a year ago); IgM anti-HAV nonreactive; anti-HCV nonreactive and HCV RNA not detected; total anti-HDV reactive; HDV RNA detected. The best interpretation is:

HDV superinfection of chronic HBV

Acute infection with a new HBV strain

A 45-year-old laboratory employee, born in a country where hepatitis B is common, has never been vaccinated against hepatitis B. Pre-employment results: HBsAg nonreactive; total anti-HBc reactive (repeat reactive, and reactive on a second manufacturer's assay); IgM anti-HBc nonreactive; anti-HBs below 2 mIU/mL; HBV DNA not detected; ALT normal. She receives one dose of hepatitis B vaccine, and anti-HBs measured 2 weeks later is 310 mIU/mL (protective at 10 mIU/mL or more). She has had no illness in the meantime. What is the best interpretation of her hepatitis B status?

Past infection with waned anti-HBs

Window period of a recent infection

A 27-year-old man had acute hepatitis B diagnosed at week 0: HBsAg reactive, HBeAg reactive, IgM anti-HBc reactive, anti-HBs nonreactive, ALT 1,420 U/L (reference < 40 U/L). His symptoms cleared by week 8. At week 28 his results are: HBsAg reactive; HBeAg reactive; IgM anti-HBc nonreactive; total anti-HBc reactive; anti-HBs nonreactive; HBV DNA 3.0 x 10^7 IU/mL; ALT 85 U/L. The same assays were used at both visits, and he reports no new exposure or illness. Which interpretation fits the week-28 results?

Chronic infection, actively replicating

Late recovery from acute hepatitis B

Window phase before anti-HBs appears

Inactive chronic HBV carrier state

During a community measles outbreak, a 13-month-old boy received his first MMR dose 11 days ago, two days after a child at his day-care center was diagnosed with measles. Yesterday he developed fever and a maculopapular rash, without cough or conjunctivitis. Results: measles IgM positive; measles IgG positive; throat swab measles RT-PCR positive. Public health staff must decide whether to begin contact tracing around him, because a true measles case would expose everyone in his clinic waiting room. Which test best tells wild-type measles from a reaction to the vaccine?

Paired acute and convalescent IgG

Viral serology (hepatitis A, B, C, EBV, HIV, CMV, rubella, measles)

35 ASCP MLS practice questions on Viral serology (hepatitis A, B, C, EBV, HIV, CMV, rubella, measles), part of Immunology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 34-year-old man who injects drugs has known chronic hepatitis B, with HBsAg reactive for 6 years and a normal ALT at his last visit a year ago. He now has jaundice and malaise. Results: ALT 1,650 U/L (reference < 40 U/L); HBsAg reactive; IgM anti-HBc nonreactive; total anti-HBc reactive; HBeAg nonreactive; anti-HBe reactive; HBV DNA 900 IU/mL (1,200 IU/mL a year ago); IgM anti-HAV nonreactive; anti-HCV nonreactive and HCV RNA not detected; total anti-HDV reactive; HDV RNA detected. The best interpretation is:
1. AHDV superinfection of chronic HBV
2. BAcute infection with a new HBV strain
3. CAcute HBV and HDV coinfection
4. DFlare of chronic hepatitis B
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Answer: A · HDV superinfection of chronic HBV
HBsAg has been present for years and IgM anti-HBc is nonreactive, so the hepatitis B is chronic, not newly acquired. The new event is hepatitis D: anti-HDV is reactive and HDV RNA is detected, while hepatitis A and C are excluded. HDV needs HBsAg for its envelope, so it can infect a person who already carries HBV (superinfection), and this usually becomes chronic hepatitis D. In coinfection both viruses arrive together and IgM anti-HBc is reactive. A flare of hepatitis B would show rising HBV DNA, whereas HDV often suppresses HBV replication, as the low, stable DNA shows here.
- B: A new acute HBV infection would make IgM anti-HBc reactive.
- C: Coinfection gives a reactive IgM anti-HBc, which is nonreactive here.
- D: A hepatitis B flare would raise HBV DNA, which is low and stable.
Question 2 · Hard
A 45-year-old laboratory employee, born in a country where hepatitis B is common, has never been vaccinated against hepatitis B. Pre-employment results: HBsAg nonreactive; total anti-HBc reactive (repeat reactive, and reactive on a second manufacturer's assay); IgM anti-HBc nonreactive; anti-HBs below 2 mIU/mL; HBV DNA not detected; ALT normal. She receives one dose of hepatitis B vaccine, and anti-HBs measured 2 weeks later is 310 mIU/mL (protective at 10 mIU/mL or more). She has had no illness in the meantime. What is the best interpretation of her hepatitis B status?
1. AWindow period of a recent infection
2. BOccult hepatitis B infection
3. CPast infection with waned anti-HBs
4. DFalse-positive anti-HBc
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Answer: C · Past infection with waned anti-HBs
Isolated anti-HBc has three main explanations: a past infection in which anti-HBs has fallen below detection, a false-positive anti-HBc, or occult infection with HBsAg below detection. A rise to 310 mIU/mL just 2 weeks after one dose is an anamnestic (memory) response, which means her immune system had met HBsAg before; in someone never vaccinated that can only have been a natural infection. A person meeting HBsAg for the first time responds slowly, with little or no anti-HBs 2 weeks after a first dose. Occult infection is unlikely with HBV DNA not detected, and a recent infection is excluded by the nonreactive IgM anti-HBc and the absence of illness. The past infection still matters if she ever needs strong immunosuppression, because HBV can reactivate.
- A: A recent infection would show reactive IgM anti-HBc, which is nonreactive.
- B: Occult infection usually shows detectable HBV DNA, which is not detected here.
- D: A true first exposure to HBsAg would give little or no anti-HBs 2 weeks after one dose.
Question 3 · Hard
A 27-year-old man had acute hepatitis B diagnosed at week 0: HBsAg reactive, HBeAg reactive, IgM anti-HBc reactive, anti-HBs nonreactive, ALT 1,420 U/L (reference < 40 U/L). His symptoms cleared by week 8. At week 28 his results are: HBsAg reactive; HBeAg reactive; IgM anti-HBc nonreactive; total anti-HBc reactive; anti-HBs nonreactive; HBV DNA 3.0 x 10^7 IU/mL; ALT 85 U/L. The same assays were used at both visits, and he reports no new exposure or illness. Which interpretation fits the week-28 results?
1. ALate recovery from acute hepatitis B
2. BWindow phase before anti-HBs appears
3. CChronic infection, actively replicating
4. DInactive chronic HBV carrier state
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Answer: C · Chronic infection, actively replicating
HBsAg that persists for more than 6 months defines chronic hepatitis B, and at week 28 it is still present with no anti-HBs. IgM anti-HBc has fallen to nonreactive as the acute phase passed, which happens in chronic as well as resolving infection, while total anti-HBc remains. A reactive HBeAg with HBV DNA of 3.0 x 10^7 IU/mL and a raised ALT shows active replication, so this is not the inactive carrier state, which has anti-HBe, low DNA and a normal ALT. Recovery would show loss of HBsAg followed by anti-HBs, and in the window phase HBsAg has already disappeared. Fewer than 5% of infected adults become chronic carriers, which is why HBsAg is checked again at 6 months.
- A: Recovery means HBsAg is cleared, usually within 6 months, and anti-HBs appears.
- B: In the window phase HBsAg has already disappeared, but here it is still reactive.
- D: An inactive carrier has anti-HBe, low HBV DNA and a normal ALT.
Question 4 · Hard
During a community measles outbreak, a 13-month-old boy received his first MMR dose 11 days ago, two days after a child at his day-care center was diagnosed with measles. Yesterday he developed fever and a maculopapular rash, without cough or conjunctivitis. Results: measles IgM positive; measles IgG positive; throat swab measles RT-PCR positive. Public health staff must decide whether to begin contact tracing around him, because a true measles case would expose everyone in his clinic waiting room. Which test best tells wild-type measles from a reaction to the vaccine?
1. AMeasles IgG avidity testing
2. BRepeat measles IgM in 2 weeks
3. CPaired acute and convalescent IgG
4. DGenotyping of the measles RNA
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Answer: D · Genotyping of the measles RNA
About 5% of children get fever and rash 7 to 12 days after MMR, and the live vaccine virus makes IgM positive and can be detected by RT-PCR, so neither serology nor a positive RT-PCR separates vaccine from wild virus. Measles vaccine strains belong to genotype A, which is not found in circulating wild measles today, so genotyping the RT-PCR product, or a vaccine-specific RT-PCR assay, answers the question. A wild genotype means measles and triggers contact tracing; genotype A means a vaccine reaction. IgG avidity is low after both a first vaccine dose and a first infection, and IgM and paired IgG rise after both. Throat swabs for RT-PCR are best collected as soon as possible after rash onset.
- A: IgG avidity is low after both a first vaccine dose and a first infection.
- B: IgM stays positive for weeks after both the vaccine and wild measles.
- C: IgG rises after both the vaccine and wild measles.
Question 5 · Medium
A first-time blood donor is HBsAg reactive, confirmed by neutralization, and HBV DNA is detected; IgM anti-HBc, total anti-HBc and anti-HBs are nonreactive. At which marked week on the hepatitis B time course shown was the donation most likely made?
Figure: MedExams
1. AWeek 40
2. BWeek 6
3. CWeek 22
4. DWeek 14
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Answer: B · Week 6
HBsAg is the first serologic marker of hepatitis B and appears weeks before anti-HBc. On the chart, only HBsAg is above the detection limit at week 6; IgM and total anti-HBc cross it at about week 9 to 10, around the onset of symptoms. The detected HBV DNA rules out the brief HBsAg reactivity that can follow a recent vaccine dose, so this is early acute infection. The unit is discarded and the donor is deferred and notified.
- A: At week 40, anti-HBs and total anti-HBc are present and HBsAg is gone.
- C: At week 22, HBsAg has cleared and only anti-HBc remains: the window period.
- D: By week 14, IgM and total anti-HBc are reactive as well.
Question 6 · Hard
A 26-year-old man has fever, sore throat and a rash 12 days after a high-risk sexual exposure. A 4th-generation HIV-1/2 antigen/antibody immunoassay is nonreactive. Based on the marker time course shown, what is the most appropriate next step?
Figure: MedExams
1. ARun an HIV-1/HIV-2 differentiation assay
2. BConfirm with an HIV-1 Western blot
3. CReport HIV infection as ruled out
4. DTest plasma for HIV-1 RNA (NAT) now
Answer and explanation in LearnFree account
Question 7 · Medium
Paired sera from four patients with a rash were tested together for rubella antibody, as shown. The patient with serologic evidence of a recent rubella infection is:
Figure: MedExams
1. APatient 3
2. BPatient 1
3. CPatient 4
4. DPatient 2
Answer and explanation in LearnFree account
Question 8 · Easy
Which serologic result confirms acute hepatitis A infection?
1. AReactive IgG anti-HAV
2. BReactive total anti-HAV
3. CReactive IgM anti-HAV
4. DReactive IgM anti-HBc
Answer and explanation in LearnFree account
Question 9 · Hard
An infant born to a mother with HIV has a reactive HIV-1/2 antigen/antibody screen at 2 months. Which test is used to diagnose HIV infection in this infant?
1. AA repeat 4th-generation screen at 6 months
2. BCD4 T-cell count and percentage
3. CHIV-1 nucleic acid test (RNA or DNA)
4. DHIV-1/HIV-2 antibody differentiation assay
Answer and explanation in LearnFree account
Question 10 · Medium
Before a kidney transplant, CMV IgG is tested in the donor (D) and recipient (R). Which pairing carries the highest risk of severe CMV disease afterwards?
1. AD-/R+
2. BD-/R-
3. CD+/R-
4. DD+/R+
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Question 11 · Medium
Total anti-HAV is reactive and IgM anti-HAV is nonreactive. This profile indicates:
1. AAcute hepatitis A infection
2. BImmunity from past infection or vaccination
3. CSusceptibility to hepatitis A
4. DA chronic hepatitis A carrier state
Answer and explanation in LearnFree account
Question 12 · Medium
HIV testing results: 4th-generation antigen/antibody immunoassay reactive; HIV-1/HIV-2 antibody differentiation assay negative for both; HIV-1 RNA detected. What do these show?
1. AA false-positive screening test
2. BAcute HIV-1 infection
3. CEstablished HIV-2 infection
4. DLong-standing HIV-1 infection
Answer and explanation in LearnFree account
Question 13 · Hard
A woman at 10 weeks of pregnancy was rubella IgG negative at booking. Three weeks after contact with a child with a rash, she develops a rash. Now: rubella IgM positive, rubella IgG 35 IU/mL (immune cutoff 10 IU/mL). The best interpretation is:
1. AFalse-positive IgM from parvovirus B19
2. BPassive antibody from immune globulin
3. CRubella reinfection in an immune woman
4. DPrimary rubella infection in early pregnancy
Answer and explanation in LearnFree account
Question 14 · Hard
An infant of an HBsAg-positive mother received hepatitis B immune globulin and the full vaccine series. At 10 months: HBsAg nonreactive, anti-HBs 120 mIU/mL, total anti-HBc reactive. The best interpretation is:
1. AVaccine failure; repeat the full series
2. BResolved HBV infection acquired at birth
3. CChronic HBV infection acquired despite prophylaxis
4. DProtected; anti-HBc is probably maternal antibody
Answer and explanation in LearnFree account
Question 15 · Hard
HBsAg has been positive for 3 years. Current results: HBeAg nonreactive, anti-HBe reactive, HBV DNA 3,500,000 IU/mL, ALT 160 U/L (reference < 40 U/L). The most likely explanation is:
1. AHepatitis B with a false-negative HBeAg assay
2. BResolving acute hepatitis B infection
3. CInactive carrier state after e seroconversion
4. DHBeAg-negative chronic hepatitis B (precore mutant)
Answer and explanation in LearnFree account
Question 16 · Hard
A 20-year-old student has had sore throat, fever and fatigue for 2 weeks. Heterophile test negative. EBV: VCA IgM negative, VCA IgG positive, EBNA antibody positive. The best interpretation is:
1. APrimary EBV infection in the early phase
2. BPrimary EBV infection, heterophile negative
3. CPast EBV infection; look for another cause
4. DNo previous EBV infection; susceptible
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Question 17 · Medium
Which finding in a newborn's serum best supports congenital rubella infection?
1. ARubella IgG equal to the mother's
2. BRubella IgG falling by 6 months
3. CRubella-specific IgM
4. DRubella IgG with high avidity
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Question 18 · Hard
At 14 weeks of pregnancy, a woman has CMV IgM positive and CMV IgG positive. CMV IgG avidity is low. What is the best interpretation?
1. AReinfection with a different CMV strain
2. BPrimary CMV infection within the past few months
3. CReactivation of a latent CMV infection
4. DPast infection, with a persistent false-positive IgM
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Question 19 · Hard
A man who recently moved from West Africa has a reactive 4th-generation HIV antigen/antibody screen. The differentiation assay is HIV-1 negative and HIV-2 positive. The best interpretation is:
1. AHIV-2 infection; HIV-1 viral loads will miss it
2. BAcute HIV-1 infection before antibodies form
3. CA false-positive screen needing no further testing
4. DHIV-1 infection with a cross-reactive HIV-2 result
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Question 20 · Medium
EBV serology: VCA IgM positive, VCA IgG positive, EBNA antibody negative. The best interpretation is:
1. AReactivation of a latent EBV infection
2. BNo previous EBV infection; susceptible
3. CCurrent or recent primary EBV infection
4. DPast EBV infection, months to years ago
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Question 21 · Hard
A 60-year-old is about to start rituximab for lymphoma. HBsAg nonreactive, total anti-HBc reactive, IgM anti-HBc nonreactive, anti-HBs nonreactive. Which test best checks for occult HBV infection?
1. AHBeAg and anti-HBe
2. BHBV DNA by nucleic acid testing
3. CRepeat HBsAg in 6 months
4. DAnti-HBs after one vaccine dose
Answer and explanation in LearnFree account
Question 22 · Easy
After exposure to hepatitis B virus, which serum marker usually becomes detectable first, often before symptoms begin?
1. AAnti-HBe
2. BAnti-HBs
3. CIgM anti-HBc
4. DHBsAg
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Question 23 · Medium
Measles IgM is negative on serum collected on the first day of a suspected measles rash. What is the best interpretation?
1. AMeasles is excluded, since the IgM test is negative
2. BThe patient must have been vaccinated earlier
3. CPast measles infection with lasting immunity
4. DToo early; IgM can be absent in the first 3 days
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Question 24 · Medium
In a person with chronic hepatitis B, a reactive HBeAg most often indicates:
1. AA low-replicative, inactive carrier state
2. BSuperinfection with hepatitis D virus
3. CActive viral replication and high infectivity
4. DThat loss of HBsAg and recovery will soon follow
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Question 25 · Hard
A 3-year-old has fever, tonsillitis, splenomegaly and many reactive lymphocytes. A rapid heterophile test is negative. EBV VCA IgM is positive and EBNA antibody is negative. The best explanation is:
1. APrimary EBV; young children often lack heterophiles
2. BA false-negative heterophile result from prozone
3. CPast EBV infection with a new, unrelated illness
4. DReactivation of latent EBV from an earlier infection
Answer and explanation in LearnFree account

10 more Viral serology (hepatitis A, B, C, EBV, HIV, CMV, rubella, measles) questions

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Study Immunology

Viral serology (hepatitis A, B, C, EBV, HIV, CMV, rubella, measles)

A first-time blood donor is HBsAg reactive, confirmed by neutralization, and HBV DNA is detected; IgM anti-HBc, total anti-HBc and anti-HBs are nonreactive. At which marked week on the hepatitis B time course shown was the donation most likely made?

A 26-year-old man has fever, sore throat and a rash 12 days after a high-risk sexual exposure. A 4th-generation HIV-1/2 antigen/antibody immunoassay is nonreactive. Based on the marker time course shown, what is the most appropriate next step?

Paired sera from four patients with a rash were tested together for rubella antibody, as shown. The patient with serologic evidence of a recent rubella infection is:

Which serologic result confirms acute hepatitis A infection?

An infant born to a mother with HIV has a reactive HIV-1/2 antigen/antibody screen at 2 months. Which test is used to diagnose HIV infection in this infant?

Before a kidney transplant, CMV IgG is tested in the donor (D) and recipient (R). Which pairing carries the highest risk of severe CMV disease afterwards?

Total anti-HAV is reactive and IgM anti-HAV is nonreactive. This profile indicates:

HIV testing results: 4th-generation antigen/antibody immunoassay reactive; HIV-1/HIV-2 antibody differentiation assay negative for both; HIV-1 RNA detected. What do these show?

A woman at 10 weeks of pregnancy was rubella IgG negative at booking. Three weeks after contact with a child with a rash, she develops a rash. Now: rubella IgM positive, rubella IgG 35 IU/mL (immune cutoff 10 IU/mL). The best interpretation is:

An infant of an HBsAg-positive mother received hepatitis B immune globulin and the full vaccine series. At 10 months: HBsAg nonreactive, anti-HBs 120 mIU/mL, total anti-HBc reactive. The best interpretation is:

HBsAg has been positive for 3 years. Current results: HBeAg nonreactive, anti-HBe reactive, HBV DNA 3,500,000 IU/mL, ALT 160 U/L (reference < 40 U/L). The most likely explanation is:

A 20-year-old student has had sore throat, fever and fatigue for 2 weeks. Heterophile test negative. EBV: VCA IgM negative, VCA IgG positive, EBNA antibody positive. The best interpretation is:

Which finding in a newborn's serum best supports congenital rubella infection?

At 14 weeks of pregnancy, a woman has CMV IgM positive and CMV IgG positive. CMV IgG avidity is low. What is the best interpretation?

A man who recently moved from West Africa has a reactive 4th-generation HIV antigen/antibody screen. The differentiation assay is HIV-1 negative and HIV-2 positive. The best interpretation is:

EBV serology: VCA IgM positive, VCA IgG positive, EBNA antibody negative. The best interpretation is:

A 60-year-old is about to start rituximab for lymphoma. HBsAg nonreactive, total anti-HBc reactive, IgM anti-HBc nonreactive, anti-HBs nonreactive. Which test best checks for occult HBV infection?

After exposure to hepatitis B virus, which serum marker usually becomes detectable first, often before symptoms begin?

Measles IgM is negative on serum collected on the first day of a suspected measles rash. What is the best interpretation?

In a person with chronic hepatitis B, a reactive HBeAg most often indicates:

A 3-year-old has fever, tonsillitis, splenomegaly and many reactive lymphocytes. A rapid heterophile test is negative. EBV VCA IgM is positive and EBNA antibody is negative. The best explanation is: