MLS Diagnostic Procedures & Reporting 3 — Questions and Answers
Question 1: A urine dipstick is positive for blood, but microscopy shows no red blood cells. The most likely explanation is:
- Contamination with vaginal flora
- Myoglobinuria or hemoglobinuria (Correct answer)
- Increased urinary bilirubin
- White cell casts in the specimen
Correct answer: Myoglobinuria or hemoglobinuria
The dipstick peroxidase reaction detects heme, so both free hemoglobin (hemoglobinuria) and myoglobin (myoglobinuria) produce a positive result in the absence of intact RBCs.
Question 2: Which coagulation test result pattern is most consistent with disseminated intravascular coagulation (DIC)?
- Prolonged PT, prolonged aPTT, decreased fibrinogen, elevated D-dimer (Correct answer)
- Normal PT, prolonged aPTT, normal fibrinogen, negative D-dimer
- Prolonged PT, normal aPTT, elevated fibrinogen, negative D-dimer
- Normal PT, normal aPTT, decreased fibrinogen, negative D-dimer
Correct answer: Prolonged PT, prolonged aPTT, decreased fibrinogen, elevated D-dimer
DIC consumes clotting factors and platelets while activating fibrinolysis, resulting in prolonged PT and aPTT, low fibrinogen, and markedly elevated D-dimer.
Question 3: A sputum Gram stain shows >25 squamous epithelial cells per low-power field. The laboratory should:
- Process the specimen and report all organisms observed
- Report the specimen as unsatisfactory and request a new sample (Correct answer)
- Perform only acid-fast bacilli culture
- Perform culture but note the poor quality in the report
Correct answer: Report the specimen as unsatisfactory and request a new sample
More than 25 squamous epithelial cells per LPF indicates heavy oral contamination, rendering the specimen unsatisfactory for lower respiratory tract culture; a repeat specimen should be requested.
Question 4: The reference interval for a laboratory test is defined as the central:
- 50% of values from a healthy reference population
- 90% of values from a healthy reference population
- 95% of values from a healthy reference population (Correct answer)
- 99% of values from a healthy reference population
Correct answer: 95% of values from a healthy reference population
Reference intervals are conventionally set to include the central 95% of values from a healthy reference population, meaning 2.5% fall below and 2.5% above the interval.
Question 5: A patient's serum appears grossly lipemic. Which of the following tests is MOST likely to be falsely elevated due to optical interference?
- Serum sodium by ion-selective electrode (indirect)
- Serum creatinine by Jaffe reaction
- Total protein by biuret method (Correct answer)
- Serum potassium by ion-selective electrode (direct)
Correct answer: Total protein by biuret method
Lipemia causes turbidity that scatters light and can falsely elevate spectrophotometric assays such as total protein by the biuret method; direct ISE methods are less affected.
Question 6: Which finding on a peripheral blood smear is characteristically associated with iron deficiency anemia?
- Macrocytes and hypersegmented neutrophils
- Microcytes, hypochromia, and pencil cells (elliptocytes) (Correct answer)
- Target cells and Howell-Jolly bodies
- Spherocytes and polychromasia
Correct answer: Microcytes, hypochromia, and pencil cells (elliptocytes)
Iron deficiency produces microcytic hypochromic red cells with pencil (cigar-shaped) cells due to reduced hemoglobin synthesis and altered membrane deformability.
Question 7: A laboratory result is reported with a delta check flag. This means:
- The result falls outside the reference interval
- The result differs significantly from the patient's previous value (Correct answer)
- The specimen was collected in the wrong tube
- The analyte is at a critical value level
Correct answer: The result differs significantly from the patient's previous value
A delta check compares the current result to the patient's most recent prior result; a flag indicates a change exceeding the defined limit, alerting staff to possible error or acute clinical change.
MLS Diagnostic Procedures & Reporting 3
A urine dipstick is positive for blood, but microscopy shows no red blood cells.
The most likely explanation is: