MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 36
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Which troponin subunit binds calcium and is identical in cardiac and slow-twitch skeletal muscle, so it is not used as a cardiac marker?
Troponin C is the calcium-binding subunit and has the same sequence in heart and slow skeletal muscle. Cardiac troponin I and T have heart-specific forms, which makes them useful markers.
A patient taking high-dose biotin supplements has a troponin result much lower than expected on a streptavidin–biotin sandwich immunoassay. Why?
In sandwich assays, excess free biotin occupies streptavidin sites on the solid phase so the labeled complex is not captured, giving falsely low results. Competitive assays give falsely high results instead.
In the lactate-to-pyruvate (forward) LD method, enzyme activity is measured as:
Lactate + NAD+ → pyruvate + NADH; NADH absorbs at 340 nm, so absorbance rises. The reverse (pyruvate-to-lactate) method measures a fall in NADH absorbance.
Under the revised Atlanta classification, which enzyme result counts as one criterion for acute pancreatitis?
Two of three are needed: typical abdominal pain, lipase or amylase at least 3 × URL, and typical imaging findings. Smaller rises occur in many non-pancreatic conditions.
A woman with fatigue, weight gain and cold intolerance has CK 900 U/L with normal troponin. She has no recent exercise, injury or injections. Which test is most useful next?
Hypothyroidism causes a myopathy with raised CK, often with these symptoms. TSH is needed before investigating for primary muscle disease. Normal troponin makes a cardiac cause unlikely.
A cholesterol sample was drawn after the tourniquet had been in place for 5 minutes. The result will most likely be:
Prolonged stasis forces water out of the vein while large particles such as lipoproteins stay, so cholesterol can rise by 5–10% or more. Tourniquet time should be kept under 1 minute.
A child with fat malabsorption, ataxia, acanthocytes on the blood film, very low cholesterol and absent apolipoprotein B most likely has a defect in:
Abetalipoproteinemia results from MTP deficiency, so apo B lipoproteins (chylomicrons, VLDL, LDL) cannot be assembled. Fat-soluble vitamin E deficiency causes the neurological signs.
A child with edema, urine protein 5 g/day and serum albumin 1.8 g/dL (18 g/L) has cholesterol 380 mg/dL (9.8 mmol/L). The main mechanism of the high cholesterol is:
In nephrotic syndrome the liver increases synthesis of albumin and apo B lipoproteins in response to low oncotic pressure; reduced clearance also contributes. It is a secondary, not a primary, hyperlipidemia.
In the enzymatic cholesterol method, cholesterol oxidase converts free cholesterol to cholest-4-en-3-one and:
Cholesterol oxidase uses oxygen and produces hydrogen peroxide, which peroxidase then uses to form a colored dye. Free fatty acids are released earlier by cholesterol esterase.
In the Evelyn–Malloy bilirubin method, which accelerator allows unconjugated bilirubin to react with the diazo reagent?
Evelyn–Malloy uses 50% methanol to release unconjugated bilirubin from albumin. Jendrassik–Grof uses caffeine–sodium benzoate instead and is less affected by protein precipitation.
A young woman has raised aminotransferases, high serum IgG, positive anti-smooth muscle antibodies and negative viral hepatitis markers. The most likely diagnosis is:
Type 1 autoimmune hepatitis shows a hepatitic enzyme pattern with raised IgG and ANA and/or anti-smooth muscle antibodies. Primary biliary cholangitis gives a cholestatic pattern with antimitochondrial antibodies.
A transcutaneous bilirubin reading in a jaundiced newborn is close to the phototherapy threshold. What is the correct next step?
Transcutaneous meters are screening tools and are less accurate at high levels, in dark skin and during phototherapy. Treatment decisions near thresholds should use total serum bilirubin.
Acute liver failure is defined as severe liver injury with an INR of 1.5 or more plus which finding, in a patient without pre-existing cirrhosis and with illness under 26 weeks?
Acute liver failure requires coagulopathy (INR ≥1.5) with any degree of encephalopathy. Very high ALT alone indicates severe injury but not liver failure.
A protein with an isoelectric point (pI) of 5.0 is placed in a buffer at pH 8.6. It will:
When buffer pH is above the pI, the protein loses protons and becomes negatively charged, so it moves toward the positive electrode (anode). At its pI it has no net charge.
A woman with iron deficiency anemia has an increased beta-1 band on serum protein electrophoresis. Which protein explains this?
Transferrin is the main beta-1 protein and rises in iron deficiency as the liver increases its synthesis. C3 forms the beta-2 band; ferritin is present in too small an amount to be seen.
A 2-year-old boy with repeated bacterial infections has an almost absent gamma band, very low IgG, IgA and IgM, and no circulating B cells. The most likely diagnosis is:
X-linked (Bruton) agammaglobulinemia is a BTK defect that stops B-cell maturation, so all immunoglobulins are very low. DiGeorge syndrome mainly affects T cells.
Total serum protein is 8.0 g/dL (80 g/L). Densitometry shows the monoclonal spike is 18% of the total area. What is the M-protein concentration?
M-protein = total protein × fraction = 8.0 × 0.18 = 1.44 g/dL. The spike is quantified by densitometry, while immunofixation is used to type it.
Proteins absorb ultraviolet light at 280 nm mainly because of which amino acids?
The aromatic rings of tryptophan and tyrosine absorb strongly near 280 nm. Peptide bonds absorb at around 200–220 nm; aliphatic and basic amino acids do not absorb at 280 nm.
A newborn with poor feeding, seizures and sweet-smelling urine has high plasma leucine, isoleucine, valine and alloisoleucine. Which enzyme is deficient?
Maple syrup urine disease is caused by failure to decarboxylate the keto acids of the branched-chain amino acids. Alloisoleucine is diagnostic. The keto acids give the urine its maple-syrup smell.
Which protein marker is used to detect sustained heavy alcohol intake over the previous 2–3 weeks?
Heavy drinking (roughly more than 50–80 g ethanol daily) reduces transferrin glycosylation, increasing carbohydrate-deficient transferrin. It normalizes after a few weeks of abstinence.