MLT GlobeQCHP exam preparation (Qatar) – page 20
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A donation is repeatedly reactive for total anti-HBc, while HBsAg and HBV NAT are negative. What happens to the unit?
Units repeatedly reactive for anti-HBc cannot be used for transfusion, because the donor may have occult HBV infection. Negative HBsAg and NAT do not overrule this.
A donor screening immunoassay is initially reactive. What is the next step?
An initially reactive result is repeated in duplicate on the same sample. If either repeat is reactive, the result is repeatedly reactive and the unit is discarded; otherwise it is considered negative.
What is the minimum interval between two plateletpheresis donations by the same donor?
Plateletpheresis donors may donate after at least 2 days, but no more than twice in 7 days and up to 24 times a year. 56 days is the interval for whole blood.
After a double red cell (2-unit) apheresis donation, the donor must wait at least:
Losing two red cell units needs longer recovery, so the interval is 16 weeks. 8 weeks applies to one whole blood unit.
What is the minimum hemoglobin for a patient donating blood for autologous use?
Autologous donors need hemoglobin of at least 11 g/dL (hematocrit 33%). Allogeneic donors must meet higher limits such as 12.5 g/dL.
Which confirmatory test must the transfusing facility perform on red cell units received from a blood supplier?
The transfusing facility confirms ABO group of every red cell unit and D type of units labelled D-negative. Weak D testing of units is not repeated.
Maternal IgG reaches the fetus by active transport across the placenta through which receptor?
FcRn on syncytiotrophoblast transports IgG, increasing sharply in the second and third trimesters. The polymeric Ig receptor carries IgA across mucosa, not placenta.
Besides being a red cell antigen carrier, the Duffy glycoprotein acts as a:
The Duffy glycoprotein (ACKR1, formerly DARC) binds chemokines and is the receptor used by Plasmodium vivax. The urea transporter is the Kidd glycoprotein; the water channel is Colton (aquaporin-1).
The biphasic IgG hemolysin in paroxysmal cold hemoglobinuria (Donath-Landsteiner antibody) usually has which specificity?
The Donath-Landsteiner antibody is an IgG anti-P that binds in the cold and activates complement on warming. Anti-I is the typical specificity in cold agglutinin disease.
A patient needs red cells. Which antibody requires antigen-negative, AHG-crossmatch-compatible units?
Anti-Fya is IgG and clinically significant, so Fy(a−) units are given. Cold-reactive Lewis, P1 and M antibodies that do not react at 37 °C/AHG usually need only crossmatch-compatible blood.
The Xga antigen is unusual because its gene is located on the:
Xga is encoded on the short arm of the X chromosome, so it is more common in females (about 89%) than males (about 66%). Anti-Xga is rarely clinically significant.
A D-positive patient makes an alloanti-D after transfusion of D-positive blood. The most likely explanation is that the patient has:
Partial D cells lack some D epitopes, so exposure to normal D can stimulate anti-D against the missing epitopes. Weak D type 1 has all epitopes, only fewer sites.
A D-negative woman has a spontaneous abortion at 9 weeks, and RhIG is to be given. Which dose is sufficient?
Before 12–13 weeks the fetal blood volume is small, so a 50 µg microdose is sufficient (a 300 µg dose is used where the microdose is unavailable). From the second trimester, the full 300 µg dose is used. Some current guidance (e.g. ACOG 2024) allows RhIG to be omitted before 12 weeks.
During red cell transfusion, a patient develops a few itchy hives only. Vital signs are normal. What is appropriate?
Mild urticaria without other signs is the only reaction in which the same unit may be restarted after treatment. A hemolytic workup is not needed for isolated hives.
Ten days after transfusion, an immunocompromised patient has fever, rash, diarrhea, abnormal liver tests and pancytopenia. Which is most likely?
TA-GVHD usually appears 8–10 days after transfusion with rash, diarrhea, liver damage and marrow aplasia. It is fatal in over 90% of cases, so prevention by irradiation is essential.
Co-oximetry determines hemoglobin fractions by:
Co-oximeters measure light absorbance at many wavelengths to quantify oxy-, deoxy-, carboxy- and methemoglobin. Saturation calculated from pO2 does not detect dyshemoglobins.
P50 is defined as:
Normal P50 is about 26–27 mmHg. A lower P50 means higher oxygen affinity (left shift); a higher P50 means lower affinity (right shift).
Base excess is best defined as:
Base excess reflects the metabolic (non-respiratory) component of acid–base status. A negative value (base deficit) indicates metabolic acidosis.
A diabetic patient with autoimmune hemolytic anemia has an HbA1c of 5.2% while home glucose readings are often above 200 mg/dL. Best explanation?
Hemolysis leaves a younger red cell population with less time to be glycated, so HbA1c is falsely low. Iron deficiency tends to raise HbA1c, not lower it.
An elderly type 2 diabetic has glucose 980 mg/dL (54 mmol/L), serum osmolality 350 mOsm/kg, pH 7.36, bicarbonate 23 mmol/L and trace ketones. This is most consistent with:
Very high glucose and osmolality with near-normal pH and bicarbonate and minimal ketones define HHS. DKA would show acidosis (pH below 7.30, low bicarbonate) and marked ketonemia.