MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 26
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A large elongated (about 25 × 12 µm) acid-fast oocyst containing one or two sporoblasts is seen in stool. The organism is:
Cystoisospora belli produces large ellipsoidal oocysts with one or two sporoblasts. It is the only intestinal coccidian commonly associated with eosinophilia.
A patient has negative HBsAg and negative anti-HBs, but positive IgM anti-HBc, 3 months after acute hepatitis symptoms. This pattern represents:
In the window period HBsAg has disappeared but anti-HBs is not yet detectable. IgM anti-HBc may be the only marker showing recent infection.
Anti-HCV is reactive but HCV RNA is not detected on repeat testing. This most likely means:
About a quarter of HCV infections clear on their own; antibody remains but RNA is absent. A false-positive antibody result is the other possibility.
Influenza pandemics are mainly caused by antigenic shift, which results from:
Influenza A has a segmented genome, so two strains infecting one host can swap segments and create a new HA or NA subtype. Point mutations cause antigenic drift and seasonal epidemics.
A patient with the Bombay (Oh) phenotype needs red cells. Which units are suitable?
Bombay plasma contains potent anti-H that is active at 37 °C and can cause severe hemolysis. Group O cells have the most H antigen, so only Oh cells are compatible; washing does not remove antigens.
When red cell units arrive from a blood supplier, the transfusion service must confirm:
AABB requires confirmation of the ABO group of all red cell units and the D type of units labelled D-negative. Weak D testing and reverse typing are not required for this confirmation.
Before an ABO-incompatible kidney transplant, what is usually done for the recipient?
ABO antigens are on vascular endothelium, so high recipient anti-A or anti-B causes hyperacute rejection. Titers are reduced by plasma exchange or immunoadsorption before transplant.
A 5-day-old group A neonate of a group O mother needs red cells. Maternal IgG anti-A is detected in the infant's plasma by IAT. Which red cells should be given?
Passive maternal anti-A would destroy group A cells, so group O cells are given until the antibody is no longer detected.
Forward typing shows group O, but the plasma contains only anti-B (A1 cells negative). To look for a weak A antigen, the best next step is:
Missing anti-A suggests a weak A subgroup. Longer incubation at room temperature or 4 °C, with anti-A,B, increases detection of weak A.
A patient on long-term methyldopa has a positive IgG DAT. The eluate reacts with all panel cells without any drug added. This indicates:
Methyldopa induces true autoantibodies that react without the drug, serologically identical to warm AIHA. Drug-dependent antibodies need drug present.
Using monospecific anti-IgG instead of polyspecific AHG in the IAT mainly helps to:
Polyspecific AHG detects C3 bound by cold antibodies. Anti-IgG avoids this, though it may miss rare complement-only Kidd antibodies.
A patient has a positive IgG DAT and a negative antibody screen. The eluate reacts with all panel cells. The most likely explanation is:
Autoantibody may be fully adsorbed onto the patient's cells, leaving none in plasma. A pan-reactive eluate points to autoantibody.
Cold-stored platelets (1–6 °C, no agitation) are used in some centres. They are mainly intended for:
Cold-stored platelets are cleared from the circulation faster but are more hemostatically active, so they suit actively bleeding patients. They are not suited to prophylaxis, where long survival is needed.
A red cell unit is divided into small neonatal aliquots with a sterile connecting device. The expiration date of each aliquot is:
A sterile connecting device keeps the system closed, so aliquots keep the original expiry. If the system is opened, a short expiry (24 hours for red cells) applies.
In the buffy coat method of preparing platelets from whole blood (common in Europe), the first centrifugation is:
The buffy coat method starts with a hard spin, separating plasma, buffy coat and red cells. Pooled buffy coats then get a light spin to collect platelets. The platelet-rich plasma method starts with a light spin.
An adult male trauma patient of unknown blood group needs red cells before any testing. The preferred uncrossmatched units are:
Group O D-positive red cells are commonly used for adult males to save scarce D-negative units. Group O D-negative is reserved for girls and women of childbearing potential.
A patient has an ABO discrepancy that cannot be resolved before urgent transfusion. Which components should be given?
Until the ABO group is resolved, give red cells that lack A and B (group O) and plasma that lacks anti-A and anti-B (group AB). This is safe whatever the true group.
To reduce the risk of TRALI, plasma for transfusion is preferably collected from:
Most TRALI cases are caused by donor HLA or HNA antibodies, often formed during pregnancy. Using plasma from males or from women tested negative for HLA antibodies reduces TRALI.
During plateletpheresis, a donor reports tingling around the lips and fingers. What is the best action?
Citrate anticoagulant binds calcium, causing mild hypocalcemia symptoms. Slowing the procedure and giving oral calcium usually relieves symptoms. More citrate would worsen them.
Donor samples are tested for HIV RNA in minipools of 16. A pool is reactive. What is the next step?
A reactive pool is resolved by testing each sample individually to find the reactive donation. Non-reactive donations from the pool can then be released.