MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 4
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A patient reports pale, clay-coloured stools. This finding reflects reduced formation in the gut of:
Stercobilin, formed from urobilinogen, gives stool its brown colour. When bile flow to the intestine is blocked, little stercobilin forms and stools become pale.
Why does unconjugated, not conjugated, bilirubin cause kernicterus in newborns?
Free (unbound) unconjugated bilirubin is lipophilic and enters the brain, especially when albumin binding is exceeded. Conjugated bilirubin is water-soluble and does not cross easily.
A hand refractometer is used to estimate total protein in serum. The method measures:
Refractometry measures refractive index, which rises with the concentration of dissolved solids, mostly protein. Absorbance at 280 nm is a separate ultraviolet method.
The preferred specimen for screening diabetic patients for albuminuria is:
A spot urine ACR, preferably first-morning, corrects for urine concentration and is recommended for screening. Standard dipsticks are insensitive to low levels of albumin.
A urine drug screen by immunoassay is positive for amphetamines. What should be done before reporting a legal (forensic) result?
Immunoassays are sensitive screens but cross-react with other drugs. A different, more specific method such as mass spectrometry is required for confirmation.
Serum calcitonin is a tumor marker for:
Medullary carcinoma arises from calcitonin-producing C cells. Papillary and follicular cancers are followed with thyroglobulin.
A visibly hemolyzed sample is received for serum iron. What effect is expected?
Red cells contain large amounts of iron in hemoglobin, and hemolysis releases it into the sample. Hemolyzed samples should be rejected for iron studies.
In developing iron deficiency, which result becomes abnormal FIRST?
Storage iron is used first, so ferritin falls before transport iron (saturation) drops. Microcytosis and low hemoglobin appear only later.
In the electrical impedance (Coulter) principle, the size of each voltage pulse is proportional to:
A cell passing through the aperture displaces conductive diluent and raises resistance; the pulse height reflects cell volume and the number of pulses gives the count. Granularity is assessed by side scatter, not impedance.
The cyanmethemoglobin (hemiglobincyanide) reference method for hemoglobin measures absorbance at:
Hemiglobincyanide has a broad absorbance peak at 540 nm, which is used in the ICSH reference method. 340 nm is used for NADH/NADPH enzyme assays.
In the Westergren ESR method (CLSI/ICSH), blood is typically:
The classic Westergren method uses 4 parts blood to 1 part 3.8% (or 3.2%) sodium citrate in a 200 mm tube, read at 60 minutes. Undiluted EDTA blood is used only in modified methods.
In a flow cytometer, which component converts emitted fluorescent light into an electronic signal?
Photomultiplier tubes (or photodiodes) detect light and convert it into electrical pulses for analysis. Dichroic mirrors only direct light of certain wavelengths to the correct detector.
Hereditary elliptocytosis is most commonly caused by a defect in:
Most hereditary elliptocytosis is due to alpha- or beta-spectrin mutations that weaken horizontal skeleton interactions, so cells cannot recover their shape. Band 3 defects cause spherocytosis or ovalocytosis instead.
On cellulose acetate electrophoresis at alkaline pH (8.4–8.6), HbC migrates in the same position as:
At alkaline pH, HbC is the slowest common hemoglobin and co-migrates with HbA2, HbE and HbO-Arab. HbD and HbG co-migrate with HbS, not with HbC.
Hydroxyurea reduces painful crises in sickle cell disease mainly by:
Hydroxyurea raises HbF, which does not enter HbS polymers and so reduces sickling. It does not change the beta-globin mutation, so HbS is not converted to HbA.
The usual adult reference interval for plasma fibrinogen is about:
Normal fibrinogen is roughly 2–4 g/L. It is an acute-phase reactant and rises in inflammation and pregnancy.
Von Willebrand factor has two main roles in hemostasis. They are:
VWF bridges platelet GPIb to exposed collagen and protects factor VIII from rapid clearance. Fibrinogen conversion is done by thrombin.
Factor V Leiden causes thrombophilia because the abnormal factor V:
The R506Q mutation removes an APC cleavage site, so factor Va stays active longer. It is the most common inherited thrombophilia in people of European ancestry.
The usual adult reference interval for the platelet count is:
Most labs use about 150–400 × 10^9/L (150,000–400,000/µL). Below 150 is thrombocytopenia and above 450 is usually called thrombocytosis.
On a well-made smear, an average of 12 platelets is seen per oil-immersion field. Using a factor of 20, the estimated platelet count is:
Estimate = average per field × 20 × 10^9/L = 12 × 20 = 240 × 10^9/L. The estimate is used to check automated counts.