MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 7
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A calibrated ocular micrometer is essential in parasitology mainly because:
Many protozoa and eggs look alike but differ in size, e.g. E. histolytica versus E. hartmanni. The micrometer must be calibrated for each objective of each microscope.
Which test confirms acute hepatitis A infection?
IgM anti-HAV is present at symptom onset and lasts about 3–6 months. IgG or total antibody may reflect past infection or vaccination.
Why must RNA viruses such as HCV and HIV undergo an extra step before PCR amplification?
Taq DNA polymerase needs a DNA template. Reverse transcription produces complementary DNA, which is then amplified (RT-PCR).
Which human papillomavirus types are most strongly associated with cervical cancer?
HPV 16 and 18 cause about 70% of cervical cancers. HPV 6 and 11 are low-risk types that cause genital warts.
In people of European descent, about what proportion of group A individuals belong to subgroup A1?
Roughly 80% of group A people are A1 and about 20% are A2. A2 is the second most common subgroup, not the majority.
Which ABO group is the least common in nearly all populations?
Group AB needs both an A and a B allele, so it is the least frequent group worldwide. Group B is less common than A in Europeans but is still more common than AB.
A group B mother has a group AB child. Which alleged father can be excluded?
The child's A allele must come from the father. A group O man carries only O alleles, so he is excluded.
By convention, reagent anti-A and anti-B are coloured:
Anti-A contains a blue dye and anti-B a yellow dye, which helps prevent reagent mix-ups.
The most common cause of acute ABO-incompatible hemolytic transfusion reactions is:
Most ABO-incompatible transfusions result from misidentification during sample collection or bedside administration, not from technical testing errors.
Group O red cells can be given to group A, B and AB patients because:
Group O cells have no A or B antigens, and people (except Bombay) do not make anti-H. They do carry much H antigen.
A patient transfused 3 weeks ago needs more red cells. The pretransfusion sample must be collected no more than how long before the transfusion?
If the patient was transfused or pregnant in the previous 3 months, the sample must be drawn within 3 days of transfusion, because new antibodies can appear quickly.
A patient had anti-Jka identified 5 years ago. Today's antibody screen is negative. Which red cells should be given?
Kidd antibodies often fall below detection but return quickly after exposure, causing delayed hemolysis. Antigen-negative units are given for life.
In the antiglobulin test, visible agglutination occurs because AHG:
IgG alone is too small to bridge cells. AHG binds Fc portions of IgG on different cells and links them.
A healthy man who was never transfused has an antibody reacting at room temperature. The most likely specificity is:
Anti-M often occurs without red cell exposure and reacts in the cold. Anti-K, anti-Fya and anti-c are usually immune antibodies.
Which coagulation factor is NOT present in useful amounts in cryoprecipitate?
Cryoprecipitate contains fibrinogen, factor VIII, von Willebrand factor, factor XIII and fibronectin. Factor IX stays in the cryo-poor supernatant, so cryo cannot treat hemophilia B.
Frozen plasma and cryoprecipitate are thawed at:
These components are thawed at 30–37 °C in a water bath (in a protective overwrap) or an approved thawing device. Higher temperatures denature proteins; lower temperatures thaw too slowly.
Red cells frozen with a glycerol cryoprotectant and stored at −65 °C or colder have a maximum shelf life of:
Frozen red cells may be stored for 10 years (longer for rare units if approved). This makes freezing useful for storing rare phenotypes.
Which information is required on the label of a pretransfusion blood sample tube?
The tube must carry two independent identifiers (such as full name and unique ID number) and the collection date, and the phlebotomist must be identifiable. Unlabeled or mislabeled samples are rejected.
At the bedside, just before transfusion begins, the most important check is:
Most fatal ABO reactions are caused by giving the right unit to the wrong patient. Two identifiers on the wristband must match the unit's compatibility label before starting.
A donor's red cells are negative with anti-D at immediate spin but positive in the indirect antiglobulin weak D test. The unit must be labeled:
Donor units must be tested for weak D, and units with weak D are labeled D-positive. Weak D cells could immunize a D-negative recipient.