MLT GlobeImmunology & Serology: Serologic tests & methods
76 Immunology & Serology MCQs on Serologic tests & methods with answers and explanations.
Which of these tests does NOT rely on an antibody tagged with an enzyme, fluorochrome or radioisotope?
The Coombs test is read as visible red-cell agglutination with unlabelled anti-human globulin. ELISA, IF and RIA each use a labelled antibody or antigen.
An Rh-negative pregnant woman is screened for anti-D, and her newborn's red cells are checked for bound maternal antibody. Which test serves both purposes?
The indirect antiglobulin test detects free anti-D in maternal serum; the direct test detects IgG coating the baby's red cells in haemolytic disease.
A reactive RPR in a pregnant woman should next be confirmed with:
RPR and VDRL detect non-treponemal (reagin) antibodies and give biological false positives in pregnancy, SLE and some infections. Treponemal tests detect antibodies to T. pallidum itself.
In an immunoprecipitation reaction, antigen excess that leads to small soluble complexes and a false-low result is called:
Postzone is antigen excess; prozone is antibody excess. Maximum lattice formation and precipitation occur at the zone of equivalence.
In a sandwich (double-antibody) ELISA for an antigen, the enzyme label is attached to:
The antigen is captured by solid-phase antibody and then detected by an enzyme-labelled antibody to a different epitope. Colour is proportional to antigen amount.
Poorly washed ELISA wells most often cause:
Inadequate washing leaves unbound enzyme conjugate in the well, which reacts with substrate and gives falsely high colour. Washing removes unbound reactants between steps.
Indirect immunofluorescence for antibodies differs from direct immunofluorescence because it uses:
In the indirect method, patient antibody binds the substrate antigen and is detected by fluorescein-labelled anti-human immunoglobulin. The direct method applies labelled antibody straight to the tissue antigen.
Which syphilis test is a treponemal test?
TP-PA detects antibodies to Treponema pallidum antigens. RPR, VDRL and USR detect non-specific antibodies to cardiolipin-lecithin-cholesterol antigen (non-treponemal tests).
Which condition is a common cause of a biological false-positive RPR?
Anti-phospholipid (cardiolipin) antibodies in SLE, pregnancy, some infections and older age can react with the RPR antigen. A treponemal test will be non-reactive.
Compared with the erythrocyte sedimentation rate, CRP as an inflammatory marker:
CRP rises within 6–12 hours of inflammation and falls quickly when it resolves (half-life about 19 hours). ESR changes slowly and is affected by red cell and plasma protein factors.
In flow cytometry, forward scatter mainly reflects a cell's:
Forward scatter light is proportional to cell size, while side scatter reflects internal complexity or granularity. Fluorescence measures antigen expression.
Chemiluminescent immunoassays generate their signal through:
Chemiluminescent labels (such as acridinium esters or luminol) emit light when oxidised, which is measured by a luminometer. Nephelometry, in contrast, measures light scattered by immune complexes.
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.
In flow cytometry, side scatter (SSC) of laser light mainly reflects a cell's:
Light scattered at about 90° (side scatter) increases with cytoplasmic granules and nuclear complexity, so granulocytes have high SSC. Cell size is mainly shown by forward scatter.
The antigen in the RPR card test consists of:
RPR uses a cardiolipin-lecithin-cholesterol (reagin) antigen bound to charcoal so flocculation is visible without a microscope. Recombinant treponemal proteins are used in treponemal immunoassays.
A lateral-flow (immunochromatographic) test shows a coloured test line but no control line. The correct interpretation is:
The control line confirms that the sample flowed correctly and reagents worked. Without it, any result is invalid regardless of the test line.
Fluorescein isothiocyanate (FITC) used in immunofluorescence emits light of which colour?
FITC absorbs blue light (about 495 nm) and emits green light (about 520 nm). Rhodamine and phycoerythrin emit orange-red light.
In the Widal test for enteric fever, the 'H' antigen refers to the:
In the Widal test, O is the somatic lipopolysaccharide antigen and H is the flagellar protein antigen. The Vi capsular antigen is used separately, mainly to detect carriers.
ELISA stands for:
ELISA is enzyme-linked immunosorbent assay, in which an enzyme label on an antibody or antigen produces a measurable colour change.
Agglutination differs from precipitation because agglutination involves:
Agglutination is the clumping of particles (cells, latex or other carriers) by antibody. Precipitation occurs when soluble antigens and antibodies form insoluble lattices.