MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 10
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Mature plasma cells usually lose CD20 and strongly express which marker?
CD138 (syndecan-1) is the standard plasma-cell marker, along with strong CD38. CD3 is a T-cell marker and CD14 marks monocytes.
Immature dendritic cells of the epidermis that capture antigen and migrate to lymph nodes are called:
Langerhans cells are skin dendritic cells that carry antigen to draining nodes and present it to naive T cells. Kupffer cells are liver macrophages.
Which IgG subclass makes up the largest proportion of total serum IgG?
IgG1 is about 60–70% of total IgG, followed by IgG2, IgG3 and IgG4. IgG2 is second.
Which complement fragments act as anaphylatoxins, causing mast cell degranulation and smooth muscle contraction?
The small 'a' fragments C3a and C5a (and weakly C4a) trigger histamine release and increase vascular permeability. C3b and C4b are opsonins and parts of convertases.
Heating serum at 56 °C for 30 minutes is done in some serological tests to:
Several complement components, such as C1 and C2, are heat-labile, while antibodies survive this treatment. Heat inactivation prevents complement from interfering with the test.
Aluminium salts are added to many inactivated vaccines to act as:
Alum adjuvants form an antigen depot and activate innate immune cells, increasing antibody responses. Preservatives such as thiomersal have a different role.
An mRNA vaccine produces immunity mainly because:
The lipid-nanoparticle mRNA is translated by host cells into the antigen, which is then presented to B and T cells. mRNA does not enter the nucleus or integrate into DNA.
Which laboratory finding is typical of untreated progressive HIV infection?
HIV destroys CD4+ T cells while CD8+ cells are often normal or increased, so the CD4:CD8 ratio falls below 1. B cells are present, often with polyclonal hypergammaglobulinaemia.
A refractometer is used in the laboratory to estimate urine specific gravity or serum total protein by measuring:
Refractive index (the bending of light) increases with dissolved solids, so it estimates specific gravity or total protein. Freezing point depression is used by osmometers.
A reagent blank is included in a colorimetric assay mainly to correct for:
The reagent blank contains reagents without sample, so its absorbance is subtracted to remove colour from the reagents. A sample blank corrects for the sample's own colour, such as haemolysis or icterus.
A blood sample has a haemoglobin of 15 g/dL and a haematocrit of 45%. The MCHC is:
MCHC = Hb ÷ Hct × 100 = 15/45 × 100 = 33.3 g/dL, within the normal range. Dividing Hct by Hb (3.0) inverts the formula.
A laboratory instrument has a three-prong plug. The third (round) prong is important because it:
The grounding prong carries stray current safely to earth if there is a fault, preventing shock. Surge protection requires separate devices.
To reduce aerosol exposure when centrifuging unstoppered blood tubes, the technologist should:
Sealed buckets or safety cups contain aerosols from broken or open tubes; they should be opened after the rotor stops, preferably in a biosafety cabinet. Opening early releases aerosols.
A patient had a right mastectomy with removal of axillary lymph nodes. Where should blood be drawn without a doctor's permission?
The arm on the side of lymph node removal may have lymphoedema and infection risk, and results may be affected. The opposite arm is used unless a doctor approves otherwise.
Which international standard specifies requirements for quality and competence of medical laboratories?
ISO 15189 is the specific standard for medical laboratory quality and competence used for accreditation. ISO 14001 covers environmental management, and ISO 9001 is a general quality standard.
Which transport medium is most suitable for a stool sample for Salmonella, Shigella and Campylobacter culture that cannot be plated within 2 hours?
Cary-Blair is a low-nutrient, semisolid transport medium with a high pH that keeps enteric pathogens alive without overgrowth. Buffered glycerol saline is poor for Campylobacter.
On eosin methylene blue (EMB) agar, Escherichia coli typically produces:
Strong lactose fermentation by E. coli produces a lot of acid, which precipitates the dyes and gives a green metallic sheen. Klebsiella usually gives pink, mucoid colonies without sheen.
A toddler whose family keeps a pet turtle develops fever and bloody diarrhoea. Which organism is most likely?
Reptiles such as turtles, lizards and snakes commonly carry nontyphoidal Salmonella, and young children are often infected through contact with them.
A Gram stain of Corynebacterium species typically shows:
Corynebacteria are pleomorphic, club-shaped gram-positive rods that snap apart during division, forming palisades and V or L shapes ('Chinese letters').
Acute rheumatic fever after group A streptococcal pharyngitis is thought to result from antibodies to which bacterial antigen that cross-react with heart tissue?
Antibodies against streptococcal M protein cross-react with cardiac myosin and other heart proteins (molecular mimicry). The hyaluronic acid capsule resembles host tissue and is poorly immunogenic.