MLT GlobeQCHP exam preparation (Qatar) – page 34
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A patient has been HBsAg positive for more than 6 months. This indicates:
Persistence of HBsAg for longer than 6 months defines chronic hepatitis B infection. Vaccination produces anti-HBs only, and resolved infection shows anti-HBs with anti-HBc.
A test with very high sensitivity is most useful for:
A highly sensitive test misses few cases, so it gives few false negatives and is well suited to screening. High specificity is more important for confirmation.
At her first antenatal visit, a pregnant woman is rubella IgG positive and rubella IgM negative. This result most likely means:
IgG without IgM indicates past infection or vaccination and immunity. Acute infection shows IgM, and a susceptible woman would be IgG negative.
Warm autoimmune hemolytic anemia is usually caused by antibodies of which class?
Warm AIHA is usually caused by IgG autoantibodies reacting best at 37 °C, detected by a positive direct antiglobulin test. Cold agglutinin disease is usually IgM.
A 1-year-old boy has eczema, recurrent ear infections and bleeding with low platelets that are small in size. Which immunodeficiency is most likely?
The triad of eczema, thrombocytopenia with small platelets and recurrent infections in a boy is typical of X-linked Wiskott–Aldrich syndrome.
An HIV-positive adult has a CD4 T-cell count of 150 cells/µL. This indicates:
A CD4 count below 200 cells/µL defines AIDS and carries a high risk of opportunistic infections such as Pneumocystis pneumonia. Normal adult CD4 counts are roughly 500–1500 cells/µL.
When a colony of Vibrio cholerae is mixed with 0.5% sodium deoxycholate on a slide, the suspension becomes viscous and forms a thread when lifted with a loop. This is the:
Vibrio cells lyse in deoxycholate, releasing DNA that forms a mucoid string; Aeromonas is usually string negative.
The yellow-green pigment of Pseudomonas aeruginosa that fluoresces under ultraviolet light is:
Pyoverdin (fluorescein) is fluorescent; pyocyanin is the blue non-fluorescent pigment, and prodigiosin is the red pigment of Serratia.
People who lack the Duffy blood group antigen on their red cells are largely resistant to infection by:
P. vivax uses the Duffy antigen as its receptor to enter red cells, so Duffy-negative people are largely protected.
The Kato-Katz thick smear technique is mainly used to:
Kato-Katz uses a template to give a fixed amount of stool, allowing eggs per gram to be calculated for intensity surveys.
In tissue, Coccidioides immitis is seen as:
Coccidioides forms thick-walled spherules containing endospores in tissue, and arthroconidia in culture.
A dimorphic mould from an HIV patient from South-East Asia produces a diffusible red pigment at 25 °C. The most likely organism is:
T. marneffei is the only dimorphic 'Penicillium', produces a red diffusible pigment and causes disseminated infection in HIV patients in South-East Asia.
In lactophenol cotton blue mounting fluid, the phenol component mainly:
Phenol kills the organism, lactic acid preserves structures and cotton blue stains the fungal wall.
Sections keep detaching from slides during a harsh staining procedure. What protective coating can be applied?
Dipping slides in dilute celloidin forms a film that holds sections in place; glycerin and oils prevent adhesion.
In electrolytic decalcification, how is calcium removed from bone?
An acid bath (typically formic plus hydrochloric acid) is used with a direct current, which attracts Ca²⁺ ions to the cathode and speeds decalcification. EDTA chelation is a separate, slower method.
A group A patient's plasma weakly agglutinates A1 reagent cells but not A2 cells. The red cells do not react with Dolichos biflorus lectin. The most likely cause is:
Dolichos biflorus lectin reacts with A1 but not A2 cells, so the patient is A2. About 1-8% of A2 and 22-35% of A2B people make anti-A1, which gives this reverse-typing discrepancy.
A donor's red cells do not react with monoclonal anti-A, react 1+ with anti-A,B, and the plasma contains anti-B but no anti-A. The most likely phenotype is:
Ax cells typically react weakly or not at all with anti-A but agglutinate with anti-A,B from group O people. A2 cells react strongly with anti-A, and Bombay plasma would contain anti-H.
Forward type: group A. Reverse: A1 cells 1+, B cells 4+, A2 cells 1+. The antibody screen is positive at immediate spin. What is the most likely cause of the discrepancy?
Reactions with both A1 and A2 cells plus a positive room-temperature screen point to a cold alloantibody (e.g., anti-M) on the reagent cells. Anti-A1 would not react with A2 cells. Use antigen-negative A1 cells after identification.
Deglycerolized red cells prepared in a closed system and stored in AS-3 at 1–6 °C expire after:
A closed-system deglycerolization device allows 14 days of storage. Open-system deglycerolized cells expire in 24 hours.
A collection bag contains 63 mL of CPD for 450 mL of blood. Only 300 mL will be collected. How much anticoagulant should be removed?
Needed anticoagulant = (300 ÷ 450) × 63 = 42 mL. The amount to remove is 63 − 42 = 21 mL. Keeping too much anticoagulant would harm red cells.