MLT GlobeDHA exam preparation (Dubai) – page 22
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
A patient develops high fever, rigors and shock soon after a platelet transfusion. Septic reaction is suspected. Which test is most important?
Suspected bacterial contamination is investigated by Gram stain and culture of the returned bag and blood cultures from the patient. Hemolysis tests are also done but do not identify sepsis.
A house fire victim has pO2 95 mmHg, calculated SO2 98%, but co-oximetry shows oxyhemoglobin 70%. The most likely explanation is:
Carbon monoxide binds hemoglobin without lowering dissolved pO2, so calculated saturation is falsely normal. Co-oximetry measures carboxyhemoglobin directly and shows reduced oxyhemoglobin.
According to ADA, level 2 (clinically significant) hypoglycemia is a glucose below:
Level 1 is below 70 mg/dL (3.9 mmol/L); level 2 is below 54 mg/dL (3.0 mmol/L); level 3 is defined by severe altered mental status, not a number.
A neonate with a hematocrit of 70% has a point-of-care meter glucose that is much lower than the laboratory plasma glucose. Most likely cause?
Many glucose meters read falsely low at high hematocrit, because less plasma reaches the strip. Glycolysis in the laboratory tube would make the laboratory value lower, not higher.
A patient with a platelet count of 1200 × 10^9/L has serum K 6.4 mmol/L but no ECG changes. What is the best next step?
Platelets release potassium during clotting, causing pseudohyperkalemia in serum when counts are very high. Plasma (heparin) potassium avoids clotting and shows the true value.
Which method is commonly used for serum magnesium on automated analysers?
Magnesium forms coloured complexes with calmagite or xylidyl blue. o-Cresolphthalein complexone is used for calcium, molybdate for phosphate and bromcresol green for albumin.
An asymptomatic woman has repeatedly raised prolactin with regular menses. Which test should be done next?
Macroprolactin (prolactin–IgG complex) is biologically inactive but detected by many immunoassays. PEG precipitation identifies it and avoids unnecessary imaging.
A 25-year-old completes a marathon. The next day CK is 3500 U/L and high-sensitivity troponin is below the 99th percentile. The best interpretation is:
Strenuous exercise damages skeletal muscle and raises CK markedly; a normal troponin argues against myocardial injury. Macro-CK usually gives a persistent, unexplained mild rise.
A patient presents 6 days after an episode of severe chest pain. Which marker is most likely to still be elevated?
Troponins remain raised for about 7–14 days after MI, allowing late diagnosis. CK-MB returns to normal in 2–3 days and myoglobin within about a day.
In the common ALP method, p-nitrophenyl phosphate is hydrolysed at alkaline pH. What is measured?
ALP removes phosphate from colourless p-nitrophenyl phosphate, producing yellow p-nitrophenoxide read at 405 nm. The rate of colour formation reflects activity.
The major apolipoprotein of HDL, which also activates lecithin-cholesterol acyltransferase (LCAT), is:
Apo A-I makes up most of HDL protein and activates LCAT, which esterifies cholesterol in HDL. Apo C-III inhibits lipoprotein lipase.
On agarose lipoprotein electrophoresis, the pre-beta band corresponds to:
Order from the anode: HDL (alpha), VLDL (pre-beta), LDL (beta); chylomicrons stay at the origin. LDL is the beta band, not pre-beta.
A newborn has severe unconjugated hyperbilirubinemia from the first days of life, does not respond to phenobarbital, and has absent UGT1A1 activity. The diagnosis is:
Crigler–Najjar type I has no UGT1A1 activity, so unconjugated bilirubin rises very high with kernicterus risk; phenobarbital does not help. Type II responds partly to phenobarbital, and Gilbert is mild.
A middle-aged woman has itching, raised ALP and GGT, and a positive antimitochondrial antibody test. The most likely diagnosis is:
Antimitochondrial antibody with a cholestatic pattern in a middle-aged woman is typical of primary biliary cholangitis. Primary sclerosing cholangitis is linked with inflammatory bowel disease and often p-ANCA.
Serum protein electrophoresis is accidentally run on heparinized plasma instead of serum. What artifact is most likely?
Fibrinogen in plasma migrates between beta and gamma and can mimic a small monoclonal band. Repeating on serum, or immunofixation, resolves the question.
In serum immunofixation electrophoresis, how are the separated proteins identified?
After electrophoresis, antisera to IgG, IgA, IgM, kappa and lambda are applied to separate lanes; immune complexes precipitate and stay after washing, then are stained. Unbound proteins wash away.
A monoclonal protein that migrates in the beta region rather than the gamma region on serum electrophoresis is most often of which class?
IgA monoclonal proteins commonly migrate in the beta region and can be hidden behind transferrin or C3, so immunofixation is important. IgG usually migrates in the gamma region.
For an aminoglycoside given as a 30-minute IV infusion, the peak level is usually drawn:
Waiting about 30 minutes after the end of the infusion allows distribution to finish. A sample just before the dose is a trough, not a peak.
To use the acetaminophen (paracetamol) treatment nomogram after a single acute overdose, blood should be drawn at least:
Absorption is incomplete before 4 hours, so earlier levels can underestimate risk. The nomogram starts at 4 hours after ingestion.
CA-125 is used mainly to monitor ovarian epithelial cancer. Which benign condition can also raise it?
CA-125 can rise in endometriosis, menstruation, pregnancy and peritoneal inflammation. This limits its use for screening in the general population.