MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 29
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Panel reactive antibody (PRA) or calculated PRA (cPRA) in a transplant candidate estimates:
cPRA expresses the percentage of the donor population with HLA antigens to which the candidate has antibodies. A high cPRA means the patient is highly sensitised and harder to match.
During serum protein electrophoresis at pH 8.6, gamma globulins move slightly toward the cathode even though they carry a small negative charge. This is caused by:
Electroendosmosis is the bulk flow of buffer toward the cathode caused by fixed negative charges on the support medium. Weakly charged gamma globulins are carried with it.
In real-time PCR, sample A has a cycle threshold (Ct) of 22 and sample B has a Ct of 32 for the same target. What does this indicate?
Ct is inversely related to the starting amount of target: fewer cycles are needed to cross the threshold when more template is present. A 10-cycle difference is roughly a 1000-fold difference.
A technologist dissolves 5.85 g of NaCl (molecular weight 58.5 g/mol) in water to a final volume of 250 mL. What is the molarity?
Moles = 5.85/58.5 = 0.1 mol. Molarity = 0.1 mol ÷ 0.25 L = 0.4 mol/L. 0.1 mol/L forgets to divide by the volume in litres.
A doubling serial dilution is set up; tube 1 contains a 1:2 dilution of patient serum. The last tube showing agglutination is tube 6. What is the titer?
In a twofold series starting at 1:2, tube n = 1:2^n. Tube 6 = 1:64. 1:32 is tube 5.
A solution reads 25% transmittance on a spectrophotometer. What is its absorbance?
A = 2 − log %T = 2 − log 25 = 2 − 1.398 = 0.602. Absorbance is not simply 1 − T (0.75); the relationship is logarithmic.
A centrifuge has a rotor radius of 10 cm and runs at 3000 rpm. Using RCF = 1.118 × 10⁻⁵ × r × rpm², the relative centrifugal force is about:
RCF = 1.118 × 10⁻⁵ × 10 × (3000)² = 1.118 × 10⁻⁵ × 9 × 10⁷ ≈ 1006 × g. rpm alone (3000) is not the same as g-force.
A high sample is diluted by mixing 1 part serum with 4 parts saline. The diluted sample reads 60 U/L. The result to report is:
1 part + 4 parts = 5 total parts, a 1:5 dilution. 60 × 5 = 300 U/L. Multiplying by 4 treats the ratio as the dilution.
How many grams of copper sulfate pentahydrate (CuSO4·5H2O, MW 249.7 g/mol) are needed to make 1 L of 0.1 mol/L CuSO4?
Grams = M × MW × L = 0.1 × 249.7 × 1 = 24.97 g. Using the anhydrous weight (159.6) would give 15.96 g, which is wrong for the hydrate.
A technologist must prepare 5.0 mL total of a 1:25 dilution of serum in saline. Which volumes are correct?
Sample volume = total volume ÷ dilution factor = 5.0/25 = 0.2 mL; add 4.8 mL saline to reach 5.0 mL. Adding 5.0 mL saline would give 1:26.
A small fire starts in a beaker of xylene. In the US classification this is a class:
Class B fires involve flammable liquids and gases such as xylene, alcohol and acetone. Class A is ordinary combustibles, C is energized electrical equipment and D is combustible metals.
For disinfecting a blood spill on a bench after absorbing the bulk material, the commonly recommended agent is household bleach diluted:
A 1:10 dilution of household bleach (about 0.5% sodium hypochlorite), freshly prepared, is recommended for large or organic-rich spills with adequate contact time.
A tourniquet is left on for 4 minutes while the phlebotomist searches for a vein. Which result is most likely to be falsely increased?
Prolonged tourniquet time causes hemoconcentration: water and small molecules move out of the vein, raising large molecules and protein-bound substances such as total protein and calcium. The limit is 1 minute.
A plasma ammonia is ordered. Which handling is correct?
Ammonia rises in vitro from red cell metabolism and deamination of amino acids. The tube (usually EDTA or heparin) should be chilled and tested quickly.
A cryoglobulin test is ordered. How should the specimen be handled until the serum is separated?
Cryoglobulins precipitate in the cold. If the sample cools before separation, they are lost in the clot and the result is falsely negative, so it is kept at 37 °C.
For a heel puncture on a newborn, CLSI recommends that the puncture depth should not exceed:
A depth of no more than 2.0 mm on the medial or lateral plantar heel avoids injury to the calcaneus, which can cause osteomyelitis.
According to CLSI guidance, serum or plasma for routine chemistry should be separated from the cells within what time after collection, unless stability data allow longer?
CLSI recommends physical separation within 2 hours to limit glycolysis and leakage of cellular contents such as potassium. Longer contact falsely lowers glucose and raises potassium.
In one run, the normal control is +2.3 SD and the abnormal control is −2.2 SD. Which rule is violated?
The range between two controls in the same run exceeds 4 SD (one above +2 SD, one below −2 SD), violating R-4s, a random error rule. Neither value exceeds 3 SD.
In an interlaboratory comparison, your lab mean is 105 mg/dL, the peer group mean is 100 mg/dL and the peer SD is 2.5 mg/dL. The standard deviation index (SDI) is:
SDI = (lab mean − peer mean) ÷ peer SD = (105 − 100) ÷ 2.5 = +2.0. A positive value means the lab reads higher than peers; |SDI| ≥ 2 suggests bias needing review.
A wound specimen is plated on phenylethyl alcohol (PEA) agar. The main purpose of this medium is to:
PEA inhibits gram-negative bacteria, including swarming Proteus, so gram-positive cocci and many anaerobes can be isolated from mixed specimens. It contains no lactose or H2S indicator.