MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 20
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
A strongly positive serum gives a negative agglutination result when tested undiluted but positive results at higher dilutions. This is:
When antibody far exceeds antigen, each antigen site is covered by separate antibodies and lattices cannot form, giving a false negative. Testing serial dilutions reveals the true positive.
An immediate-spin crossmatch is mainly designed to detect:
Immediate-spin (room temperature) crossmatching confirms ABO compatibility when the antibody screen is negative. Clinically significant IgG antibodies need an antiglobulin (AHG) crossmatch.
Acute hypoxemia with bilateral lung infiltrates within 6 hours of plasma transfusion, without volume overload, suggests:
TRALI is usually caused by donor anti-HLA or anti-HNA antibodies that activate recipient neutrophils in the lung. Unlike TACO, there are no signs of fluid overload such as raised BNP or response to diuretics.
Failure of serum cortisol to suppress after a 1 mg overnight dexamethasone test suggests:
Dexamethasone normally suppresses ACTH and so cortisol. Persistent cortisol (above about 1.8 µg/dL) suggests autonomous cortisol production. Addison disease is investigated with an ACTH stimulation test.
pH 7.30, pCO2 30 mmHg, HCO3 14 mmol/L. This is:
Low pH with low bicarbonate is metabolic acidosis. The low pCO2 shows the lungs are blowing off CO2 to compensate, but pH is not yet normal.
A plasma sample left overnight at 4 °C shows a creamy top layer over clear plasma. This indicates:
Chylomicrons are large and light, so they float as a cream layer on standing. A turbid infranatant would suggest excess VLDL as well.
A small gram-negative coccobacillus grows on blood agar only around a Staphylococcus aureus streak and needs both X and V factors. It is:
S. aureus lyses red cells (releasing X, hemin) and secretes V (NAD), so H. influenzae grows as satellite colonies next to it. H. parainfluenzae needs only V factor.
Seven consecutive control values fall on the same side of the mean, all within ±2 SD. This is a:
A sudden run of values on one side of the mean is a shift, often from a new reagent lot or calibration change. A gradual drift in one direction is a trend (e.g. lamp ageing).
The H gene (FUT1) encodes an enzyme that adds which sugar to the precursor chain on red cells?
FUT1 fucosyltransferase adds L-fucose to the terminal galactose of type 2 precursor chains, making H antigen, the substrate for A and B transferases.
Expression of A, B and H substances in saliva and other secretions is controlled mainly by which gene?
The Se gene (FUT2) makes H on type 1 chains in secretory tissues. FUT1 controls H on red cells; without Se, no soluble ABH is secreted even if FUT1 is normal.
A group A patient has a positive autocontrol at room temperature and agglutinates both A1 and B reagent cells weakly. Forward typing gives weak reactions with anti-B as well. The most likely cause is:
A strong cold autoagglutinin coats the patient's cells (causing false forward reactions) and reacts with all reagent cells. Washing cells in warm saline and prewarming the reverse type help resolve it.
A group O mother and a group AB father can have children of which ABO groups?
The mother gives O; the father gives A or B. Children are AO (group A) or BO (group B). Group O or AB children would not be expected.
During reverse typing, the supernatant in the B-cell tube is clear red and no cell button remains. How should this be interpreted?
ABO antibodies can activate complement and lyse reagent cells when serum is used. Hemolysis is a positive reaction and is recorded as such.
Why are A1 cells, not A2 cells, used as the routine A reagent cell for reverse typing?
A1 cells carry the most A antigen, so they reliably detect anti-A. A2 cells are used only when checking for anti-A1.
Screening cells are chosen so that some are homozygous for antigens such as Jka, Fya and c. The main reason is to:
Weak antibodies with dosage (e.g. Kidd, Duffy, Rh) may react only with double-dose cells. Homozygous expression improves detection of these clinically significant antibodies.
A patient transfused 2 weeks ago has a warm autoantibody. Why should autologous adsorption NOT be used?
Donor cells still circulating in the sample may carry antigens that remove the patient's alloantibodies. Allogeneic (differential) adsorption with phenotyped cells is used instead, usually if transfusion was within about 3 months.
When preparing an eluate, the last wash of the cells is also tested. Its purpose is to show that:
If the last wash reacts, free plasma antibody remains and may give false eluate reactivity. A nonreactive last wash shows that the eluate contains only antibody removed from the cells.
After a negative antiglobulin test, IgG-coated check cells are added and do not agglutinate. The most likely cause is:
Check cells should react with free anti-IgG. No reaction means the AHG was neutralized by leftover plasma globulin, was not added, or was inactive, so the test is invalid and must be repeated.
Which error can cause a FALSE-POSITIVE antiglobulin test result?
Excess centrifugation packs cells tightly so they are hard to resuspend and look agglutinated. Delay after washing lets IgG elute and causes false negatives; a heavy suspension also weakens reactions.
Cryoprecipitate pooled in an open system and kept at 20–24 °C must be transfused within:
Open-system pooled cryoprecipitate expires in 4 hours. Single units or closed-system pools may be kept for 6 hours after thawing.