MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 19
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
The prewarm technique in antibody testing is used to:
Cells and plasma are warmed to 37 °C separately before mixing, so cold antibodies cannot bind and carry into the AHG phase. It may weaken some clinically significant antibodies, so it is used with care.
A patient given intravenous immunoglobulin (IVIG) now has weak anti-A and anti-D in the plasma, with no history of exposure. The most likely source is:
IVIG is pooled from many donors and can contain ABO and other antibodies. Passive antibodies are usually weak and disappear within weeks.
Which change occurs in red cells during storage at 1–6 °C?
The storage lesion includes potassium leak from cells, falling pH, and loss of ATP and 2,3-DPG. 2,3-DPG decreases, not increases.
Leukocyte reduction helps prevent all of these EXCEPT one. Which complication is NOT prevented?
Filters leave enough viable T lymphocytes to cause TA-GVHD; only irradiation or approved pathogen reduction prevents it. Leukoreduction does reduce FNHTR, HLA alloimmunization and CMV risk.
A patient will receive red cells donated by his brother. The unit must be:
Blood from blood relatives may share HLA haplotypes, so donor lymphocytes may not be rejected and can cause TA-GVHD. Irradiation prevents this.
A rejuvenation solution containing pyruvate, inosine, phosphate and adenine is used to:
Rejuvenation restores 2,3-DPG and ATP in red cells near expiry; the cells are then washed and may be frozen or transfused within 24 hours.
On inspection, a red cell bag is dark purple while its attached segments are normal red. The most likely cause is:
A color difference between the bag and its segments suggests bacterial growth (e.g., Yersinia) with hemolysis and low oxygen. The unit must be quarantined and not issued.
A D-negative woman aged 28 must receive D-positive apheresis platelets. To prevent anti-D formation, she should receive:
Platelet units contain small amounts of D-positive red cells that can immunize. Rh immune globulin (a standard 300 µg dose covers many units) prevents anti-D.
A routine major crossmatch will usually NOT detect:
A D-negative patient without anti-D gives a compatible crossmatch with D-positive cells, so D typing errors are missed. ABO mismatch, antibodies to donor antigens and a donor positive DAT can all give incompatibility.
For adult patients, which component is usually issued without regard to ABO compatibility?
Cryoprecipitate has very little plasma per unit, so ABO antibodies are negligible in adults. Granulocytes contain many red cells and must be ABO-compatible.
Which mosquito-borne virus is screened by NAT on blood donations in the United States?
West Nile virus NAT has been required for US donations since 2003, with individual-donation testing when local activity is high. Dengue and chikungunya are not routinely screened there.
A healthy long-distance runner has a regular pulse of 46 per minute. Other findings are normal. The donor:
The usual pulse range is 50–100 per minute, but a lower regular pulse in a healthy athlete is acceptable after evaluation. Bradycardia here is physiological, not disease.
In many laboratories, a maternal anti-D titer in which range is considered 'critical', prompting fetal monitoring for anemia?
A titer of 16 or 32 (set by each laboratory) is usually taken as critical. Below this, severe HDFN is unlikely and titers are simply repeated during pregnancy.
Which non-invasive test is now preferred to detect moderate to severe fetal anemia in an alloimmunized pregnancy?
An anemic fetus has lower blood viscosity and higher cardiac output, so MCA peak velocity rises. This Doppler test has largely replaced amniocentesis.
Which set of requirements fits red cells prepared for intrauterine transfusion in anti-D HDFN?
The cells must lack the antigen of the maternal antibody, be irradiated to prevent TA-GVHD, and be crossmatched with maternal plasma. They are also fresh, CMV-risk-reduced, HbS-negative and highly concentrated.
A D-negative mother received RhIG at 28 weeks. Her D-positive newborn has a weakly positive DAT and no anemia or jaundice. The best explanation is:
Some RhIG crosses the placenta and can weakly coat fetal D-positive cells. This rarely causes hemolysis; the mother is still eligible for postpartum RhIG.
Reconstituted whole blood for exchange transfusion in HDFN is usually prepared from group O red cells suspended in plasma of group:
Group AB plasma has no anti-A or anti-B, so it cannot harm the infant's cells whatever the infant's ABO group. Group O red cells are compatible with maternal anti-A and anti-B.
Why is hyperbilirubinemia rarely a problem for the fetus before birth in HDFN?
Unconjugated bilirubin passes to the mother and is cleared by her liver. After birth, the immature newborn liver cannot conjugate enough, so bilirubin rises quickly.
After anti-D, which Rh antibody most often causes severe HDFN?
Anti-c can cause severe HDFN requiring intrauterine or exchange transfusion. Anti-C, anti-e and anti-Cw usually cause mild disease.
A patient has made anti-k (anti-Cellano). About what proportion of random donors will be k-negative?
The k antigen is high-prevalence (present in about 99.8% of people), so k-negative (K+k−) donors are rare. About 91% of people are K-negative, not k-negative.