MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 18
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
Why must tissue be well fixed before it is placed in alcohol for dehydration?
Fixation stabilizes proteins so the tissue withstands dehydration, clearing and hot wax. Unfixed tissue shrinks, hardens and distorts in graded alcohols.
Type I collagen is the dominant fibre in which tissue?
Type I collagen predominates in dermis, bone and tendon. Basement membranes contain type IV, lymphoid stroma type III (reticulin) and hyaline cartilage type II.
Direct immunofluorescence on a fresh renal biopsy is used to demonstrate:
Fluorescein-labelled antibodies against immunoglobulins and complement localize deposits in glomerular disease. Amyloid and calcium are shown by other methods.
Masson trichrome typically uses which dye combination?
Weigert's iron haematoxylin stains nuclei, Biebrich scarlet–acid fuchsin stains muscle red and aniline blue stains collagen blue.
Which immunostain gives a nuclear staining pattern?
Ki-67 is located in the nucleus of proliferating cells. Cytokeratin and vimentin are cytoplasmic filaments, and CD45 is a membrane antigen.
A mutation found in about 95% of patients with polycythemia vera is:
JAK2 V617F (or, less often, a JAK2 exon 12 mutation) is present in nearly all cases of PV. CALR and MPL mutations are seen in essential thrombocythemia and primary myelofibrosis; FLT3-ITD is an AML mutation.
Which cardiac marker rises earliest after myocardial injury but has poor cardiac specificity?
Myoglobin is a small protein that appears in blood within 1-3 hours of muscle injury. Because skeletal muscle also contains it, a raised level is not specific for the heart; its main value is a negative result early on.
'Beta-gamma bridging' on serum protein electrophoresis is characteristic of:
In cirrhosis, polyclonal IgA rises and runs between the beta and gamma zones, filling the dip between them. Albumin is also usually low.
Macro-ovalocytes, hypersegmented neutrophils and raised methylmalonic acid with neurological symptoms indicate deficiency of:
Both B12 and folate deficiency cause megaloblastic anemia with hypersegmented neutrophils. Methylmalonic acid rises only in B12 deficiency, and neurological damage is a feature of B12 deficiency.
An analyser reports platelets of 40 × 10^9/L in a well patient with no bleeding. The smear shows platelet clumps. The best action is:
EDTA can expose platelet antigens that antibodies bind, causing clumps and a falsely low count (pseudothrombocytopenia). Citrate usually prevents it; multiply the count by 1.1 for the dilution.
Why is ABO hemolytic disease of the newborn seen mostly in babies of group O mothers?
Group O people have anti-A,B with a significant IgG component, which crosses the placenta. In group A and B mothers, anti-B or anti-A is mostly IgM and does not cross.
A patient with multiple myeloma has extra positive reactions with both A1 and B reagent cells. Cells look like stacks of coins under the microscope. The best way to resolve this is:
Raised globulins cause rouleaux, which mimics agglutination. Replacing plasma with saline disperses rouleaux while true agglutination remains. Enzyme treatment would increase, not remove, the false reactions.
A group A patient was given group O red cells in an emergency. Next day the red cells show a mixed-field reaction with anti-A. The most likely explanation is:
After transfusion of group O cells, a mixture of the patient's A cells and donor O cells gives mixed-field agglutination with anti-A. Weak subgroups can give mixed field, but the recent transfusion explains it here.
A cord blood sample gives weak nonspecific agglutination in all ABO forward-typing tubes. What is the most likely cause?
Wharton's jelly from the umbilical cord can cause nonspecific clumping of cord cells. Washing the cells several times in saline removes it.
A patient with acute myeloid leukemia was typed as group A last year. Today the cells react only weakly with anti-A, and the reverse typing is unchanged. The most likely explanation is:
Hematologic malignancies, especially leukemias, can reduce A or B antigen expression (a group II discrepancy). Antigen strength often returns with remission.
Anti-A1 is found more often in people of which phenotype?
Anti-A1 occurs in a small minority of A2 people but in a much larger proportion (about a quarter or more) of A2B people. A1 and A1B people do not make anti-A1.
To confirm an antibody identification at p ≤ 0.05 by the classic 'rule of three', you need:
Three antigen-positive reactive cells and three antigen-negative nonreactive cells give a probability of about 1 in 20 that the pattern is due to chance. Reactive cells alone do not exclude random reactions.
A never-transfused patient with warm autoimmune hemolytic anemia has pan-reactive plasma. Which method best detects underlying alloantibodies?
The patient's own cells, after removing bound autoantibody, adsorb only autoantibody and leave alloantibodies in the plasma. This is safe only when the patient has not been transfused recently.
Why is an EDTA sample preferred for the direct antiglobulin test?
EDTA chelates calcium and magnesium needed for complement activation, so any C3 found reflects in vivo binding. Clotted samples stored cold can pick up complement in vitro.
A 70-year-old with painful blue fingers in cold weather has a DAT positive with anti-C3d and negative with anti-IgG. This pattern best fits:
Cold IgM autoantibodies bind in the cold, fix complement, then detach on warming, leaving only C3d. Warm AIHA usually shows IgG with or without C3.