MLT GlobeMOH exam preparation (UAE) – page 16
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
On average, people of group O have lower plasma levels of:
VWF carries ABH antigens, and group O VWF is cleared faster, so levels are about 25% lower. This must be considered when interpreting VWF results.
For a patient with sickle cell disease starting chronic transfusion, many programs give units matched for which antigens to prevent alloimmunization?
Anti-C, anti-E and anti-K are the most frequent alloantibodies in these patients, so prophylactic matching lowers alloimmunization.
Apheresis platelets stored at 20–24 °C with agitation, and with no additional bacterial risk-control step, expire after:
Conventional room-temperature platelets have a 5-day shelf life because of the risk of bacterial growth. Seven-day dating is allowed only when an extra bacterial risk-control strategy is used.
Why is the collection bag gently mixed throughout whole blood donation?
Continuous mixing distributes the anticoagulant evenly so small clots do not form. Clots make the unit unusable and can block filters.
Why do Lewis antibodies not cause HDFN?
Lewis antibodies are usually IgM, which cannot cross the placenta, and fetal and newborn red cells express little Lewis antigen.
Compared with ABO antigens, Rh antigens on fetal and newborn red cells are:
Rh antigens are well expressed early in fetal life, which is why Rh antibodies can cause severe fetal disease. ABO antigens are weaker at birth.
Apart from anti-D, which Rh antibody most often causes severe hemolytic disease of the fetus and newborn?
Anti-c is the Rh antibody after anti-D most often linked to severe HDFN. Anti-C and anti-e usually cause mild disease.
In gas chromatography, a drug in a sample is identified mainly by comparing its:
Each compound passes through the column in a characteristic time (retention time) under set conditions; matching it with a standard identifies the compound. Peak area gives the quantity.
A total cholesterol is 200 mg/dL. Cholesterol has a molecular weight of 386.7 g/mol. The result in SI units is about:
200 mg/dL = 2000 mg/L; 2000 ÷ 386.7 = 5.17 mmol/L. Forgetting to convert dL to L gives 0.52 mmol/L.
Serum results are sodium 138 mmol/L, chloride 102 mmol/L and bicarbonate 24 mmol/L. Using Na⁺ − (Cl⁻ + HCO₃⁻), the anion gap is:
Anion gap = 138 − (102 + 24) = 12 mmol/L. Adding potassium would give about 16 mmol/L, but this formula does not include potassium.
A fire starts in a container of burning sodium metal. Which extinguisher class is designed for this?
Class D extinguishers (dry powder) are for combustible metals such as sodium, potassium and magnesium. Water can react violently with these metals.
Work with Ebola virus or other agents causing life-threatening disease with no available treatment requires which biosafety level?
BSL-4 is for dangerous exotic agents with high risk of life-threatening disease and no vaccine or treatment, using positive-pressure suits or Class III cabinets. BSL-3 is for agents like M. tuberculosis.
Which statement about needle gauge is correct?
Gauge is inversely related to bore diameter: a 23 G needle is thinner than a 21 G needle. Routine adult venipuncture commonly uses 21–22 G; 16 G is used for blood donation.
A new test is performed on 200 people known to be free of the disease. It is negative in 170 and positive in 30. What is its specificity?
Specificity = true negatives / all people without disease = 170/200 = 85%. The false-positive rate is 30/200 = 15%.
A correct result is transcribed into the wrong patient's record during manual entry. This is an error in which phase?
Reporting, transcription and communication of results are post-analytical steps. The measurement itself was correct, so it is not an analytical error.
Sabouraud dextrose agar favours the growth of fungi over most bacteria mainly because of its:
The low pH and high sugar content suppress many bacteria while fungi grow well. Cycloheximide is added only in modified formulas and inhibits saprophytic moulds, not bacteria.
A pleural exudate has a very low glucose (below 30 mg/dL or 1.7 mmol/L) in a patient with a long history of symmetrical joint disease. The most likely cause is:
Rheumatoid pleural effusions characteristically have very low glucose because of impaired glucose transport and high cell metabolism. Heart failure, cirrhosis and nephrotic syndrome cause transudates with normal glucose.
Amniotic fluid alpha-fetoprotein is raised and acetylcholinesterase is positive. This most strongly suggests:
Leakage of fetal CSF through an open neural tube defect raises AFP, and acetylcholinesterase confirms neural tissue origin. Down syndrome is associated with low, not high, AFP.
Which reagent strip pad requires the longest reaction time, about 2 minutes, before reading?
The leukocyte esterase reaction is slow and is read at about 2 minutes; most other pads are read between 30 and 60 seconds.
Colourless, octahedral 'envelope' crystals are seen in a normal acidic urine. They are:
Calcium oxalate dihydrate forms envelope-shaped crystals, common in acidic and neutral urine and often diet related. Triple phosphate forms 'coffin-lid' prisms in alkaline urine.