MLT GlobeQCHP exam preparation (Qatar) – page 36
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A total hemolytic complement (CH50) result is zero, while the alternative pathway (AH50) activity is normal. The defect most likely lies in:
CH50 tests the classical and terminal pathway; AH50 tests the alternative and terminal pathway. Normal AH50 means C3 and C5–C9 work, so the defect is in C1, C4 or C2.
According to the 2021 WHO definitions, an MDR-TB isolate that is also resistant to levofloxacin and to bedaquiline is classified as:
XDR-TB is MDR/RR-TB with resistance to any fluoroquinolone plus at least one of bedaquiline or linezolid. Pre-XDR-TB is MDR/RR-TB with fluoroquinolone resistance only.
Candida auris differs from Candida albicans in that C. auris typically:
C. auris grows well at 40–42 °C, does not produce germ tubes, and rarely forms hyphae or chlamydospores. Chlamydospore production on cornmeal agar is characteristic of C. albicans.
A dimorphic fungus grows as a mold at 25 °C and as a yeast at 37 °C. Which organism is NOT dimorphic in this way?
In tissue Coccidioides forms spherules containing endospores, not yeast cells. Histoplasma, Blastomyces and Talaromyces all show classic mold-to-yeast thermal dimorphism.
A 2-year-old has septic arthritis of the knee. Routine plating of the joint fluid shows no growth. Which step most improves recovery of the most likely fastidious organism?
Kingella kingae is a major cause of bone and joint infection in children under 4 and grows poorly on plates. Inoculating joint fluid into blood culture bottles (or using PCR) greatly improves detection.
A 4th-generation HIV screen is reactive, but the HIV-1/HIV-2 differentiation assay is negative. What should be done next?
This pattern may be acute HIV infection, when p24 antigen is present before antibodies. HIV-1 NAT resolves it: a positive result shows acute HIV-1 infection.
On day 3 of illness, a dengue patient has high dengue IgG, and IgM is low or absent. This pattern suggests:
In secondary infection, IgG rises rapidly and early while IgM is low. Secondary infection with a different serotype has higher risk of severe dengue due to antibody-dependent enhancement.
A group B donor's red cells react weakly with one monoclonal anti-A clone but not with other anti-A reagents. The plasma has strong anti-A, and secretor saliva contains B and H only. The best explanation is:
In B(A), a highly active B transferase adds small amounts of GalNAc, detected by some sensitive monoclonal anti-A clones. Cis-AB would give weak A and B with usually weak anti-B, not strong anti-A with normal B.
During shipment, platelets may be held at room temperature without agitation for a maximum of:
Platelets may go up to 24 hours without agitation, as in transport. Longer periods without agitation cause pH to fall and reduce platelet quality.
Why can anti-K cause severe fetal anemia with relatively little rise in amniotic fluid bilirubin?
Kell antigens appear on early erythroid progenitors, so anti-K suppresses red cell production as well as causing hemolysis. Bilirubin and titers therefore underestimate the anemia.
In a jaundiced newborn with HDFN, why are drugs such as sulfonamides avoided?
Only unbound unconjugated bilirubin crosses the blood-brain barrier. Drugs that displace bilirubin from albumin raise free bilirubin and the risk of kernicterus.
A newborn of a mother with high-titer anti-D types D-negative, but the DAT is strongly positive with IgG. The most likely explanation is:
In 'blocked D', heavy coating with maternal anti-D leaves no free sites for the typing reagent, causing a false D-negative type. An eluate showing anti-D or a monoclonal IgM test can confirm.
The Kell glycoprotein is a:
Kell is a zinc endopeptidase that can activate big endothelin-3. Urea transport is the Kidd protein and chemokine binding is Duffy.
The Gerbich-negative Leach phenotype, which lacks glycophorins C and D, is associated with:
Glycophorin C links the membrane to the cytoskeleton through protein 4.1; its absence gives elliptocytes. Vivax resistance relates to Duffy-negative cells.
A diabetic with vomiting has Na 140, Cl 94, HCO3− 20 mmol/L (normal anion gap 12). Comparing change in anion gap with change in HCO3−, which additional disorder is present?
AG = 140 − (94 + 20) = 26, a rise of 14, while HCO3− fell only 4. A delta ratio of 3.5 (above 2) means bicarbonate is higher than expected, showing a coexisting metabolic alkalosis from vomiting.
During recovery from acute viral hepatitis, ALT stays raised longer than AST mainly because:
ALT has a half-life of about 47 hours compared with about 17 hours for AST, so AST falls faster once liver cell damage stops.
A sample with normal triglycerides shows an extra pre-beta band on lipoprotein electrophoresis. On ultracentrifugation it does not float with VLDL but sinks into the LDL density range. This band is most likely:
Lp(a) has pre-beta mobility but is denser than VLDL, so it is called 'sinking pre-beta'. Beta-VLDL of type III disease floats at density 1.006 and gives a broad beta band.
On agarose electrophoresis at pH 8.6, gamma globulins may move slightly toward the cathode, behind the application point. This is caused by:
The fixed negative charges of the support attract positive ions that flow toward the cathode, carrying water with them. This flow pulls weakly charged gamma globulins backward.
A tall boy with dislocated lenses, learning difficulty and venous thrombosis has very high plasma total homocysteine and high methionine. Which enzyme is most likely deficient?
Classic homocystinuria (CBS deficiency) blocks homocysteine conversion to cystathionine, so both homocysteine and methionine rise. In MTHFR deficiency methionine is low or normal.
In capillary electrophoresis immunosubtraction, serum is incubated with anti-IgG and anti-kappa beads in separate runs. The M-peak disappears in both runs. The M-protein is:
The beads remove proteins that carry the matching heavy or light chain, so the peak vanishes only with the correct antisera. Loss with both anti-IgG and anti-kappa identifies IgG-kappa.