MLT GlobeQCHP exam preparation (Qatar) – page 30
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A cell in a marrow aspirate has a round central nucleus fully visible, and many dark purple granules that do not cover the nucleus. It is larger than a basophil. It is most likely a:
Mast cells are large tissue cells with a round nucleus and dense purple granules; they are found in marrow and tissue, not normal blood. Basophil granules usually cover and obscure a lobed nucleus.
A Wright-stained smear shows red cells bluish-grey, eosinophil granules grey-blue and dark nuclei. The most likely cause is:
An alkaline stain or buffer makes everything too blue, including red cells and eosinophil granules. A pH that is too acidic gives bright red cells, pale nuclei and very red eosinophil granules.
A Wright-stained smear shows bright red cells, very pale blue nuclei and brilliant red eosinophil granules. The first thing to check is:
Overly acidic buffer (below about pH 6.4) causes too much eosin uptake and weak nuclear staining. Long staining or thick smears generally make slides too blue.
A patient with disseminated fungal infection has small oval yeasts, each with a clear halo, inside monocytes and neutrophils on a blood smear. The organism is most likely:
Histoplasma yeasts (2–4 µm) are seen within phagocytes in disseminated disease, especially in immunosuppressed patients. Anaplasma forms morulae, and Plasmodium and Babesia infect red cells.
A patient has WBC 0.8 × 10^9/L and a differential is needed. The best way to find enough cells is:
Buffy coat smears concentrate leukocytes from centrifuged blood, allowing a meaningful differential in severe leukopenia. The thick part of a smear has distorted, overlapping cells.
A 'basket' or smudge cell differs from a necrobiotic neutrophil because the smudge cell:
Smudge cells are fragile cells broken during smear making, leaving only a spread-out nucleus. Apoptotic (necrobiotic) neutrophils keep cytoplasm with dense, round, pyknotic nuclear pieces.
A urine cytology sample from a kidney transplant recipient shows enlarged cells with a single, homogeneous, glassy dark nuclear inclusion. These 'decoy cells' indicate:
Decoy cells carry polyomavirus inclusions that can mimic malignant cells but are benign; in transplant patients they suggest BK virus reactivation. Herpes shows multinucleation and nuclear molding.
Tangled clumps of thin filamentous bacteria, forming 'cotton ball' masses on a Pap smear, are most often seen in women:
Actinomyces-like organisms are strongly associated with intrauterine device use. The finding is reported under organisms in the Bethesda System.
ASCO/CAP guidelines state that a breast resection for ER, PR and HER2 testing should be placed in fixative within:
Cold ischemia time should be as short as possible and no more than 1 hour, because antigens and nucleic acids degrade before fixation. The time to fixation should be documented.
In a combined Alcian blue (pH 2.5)–PAS stain of intestinal mucosa, neutral mucins appear:
Alcian blue stains acid mucins blue, then PAS stains the remaining neutral mucins magenta; cells with both appear purple. This helps detect intestinal metaplasia.
Repeated subcutaneous injections of an antigen in a sensitised person cause local oedema, haemorrhage and necrosis at the site after 4–8 hours. This is called:
The Arthus reaction is a localised type III reaction: circulating IgG meets injected antigen in the vessel wall, forming complexes that fix complement. Serum sickness is the systemic form of type III disease.
Before a peripheral blood stem cell transplant, the harvested product is counted for haematopoietic progenitor cells. Which marker is used?
CD34 identifies haematopoietic stem and progenitor cells and is used to calculate the graft dose. CD138 marks plasma cells, and CD25 is the IL-2 receptor alpha chain.
Which chemokine released by macrophages and epithelial cells is a major attractant for neutrophils?
CXCL8 (IL-8) binds CXCR1/CXCR2 on neutrophils and draws them to sites of infection. IL-7 is a lymphocyte growth factor, not a chemokine.
HIV enters CD4 T cells by binding CD4 together with which coreceptor?
HIV gp120 binds CD4 and then a chemokine receptor, CCR5 (R5 strains) or CXCR4 (X4 strains). CD21 is the EBV receptor.
During negative selection in the thymus, thymocytes are deleted when their T-cell receptor:
Strong binding to self-peptide–MHC signals a potentially autoreactive cell, which dies by apoptosis (central tolerance). Cells that bind no MHC die by neglect, not negative selection.
Each B cell produces antibody from only one of its two heavy-chain alleles. This is called:
Once one allele is productively rearranged, rearrangement of the other is stopped, so each B cell has a single specificity. Isotype switching changes the constant region, not the allele used.
Antibody affinity for an antigen increases during the weeks after immunisation. This is mainly due to:
Point mutations in variable-region genes, followed by selection of B cells that bind antigen best, produce affinity maturation. Light-chain type does not change affinity in this way.
The HLA class III region of the MHC encodes:
Class III genes lie between class I and II and include C2, C4, factor B and TNF. β2-microglobulin is encoded outside the MHC, on chromosome 15.
A patient with suspected coeliac disease has HLA typing. Absence of which alleles makes coeliac disease very unlikely?
Nearly all coeliac patients carry HLA-DQ2 or DQ8, so a negative result has a very high negative predictive value. HLA-B27 relates to spondyloarthritis.
IgG has a serum half-life of about 3 weeks, much longer than other classes. This is mainly because:
FcRn binds IgG in endosomes and recycles it back to the circulation instead of letting it be degraded. IgG has no J chain or secretory component.