Medical Laboratory Technician Exam ASCP Medical Laboratory Technician 1 — Questions and Answers
Question 1: A urine specimen tested by dipstick shows a positive result for blood but microscopic examination reveals no red blood cells. Which condition best explains this discrepancy?
- Urinary tract infection with white cell casts
- Myoglobinuria from rhabdomyolysis (Correct answer)
- Contamination with vaginal secretions
- Renal tubular acidosis
Correct answer: Myoglobinuria from rhabdomyolysis
Dipstick blood reagent pads react with hemoglobin AND myoglobin due to their shared peroxidase-like activity. Myoglobinuria (from muscle breakdown) produces a positive dipstick without intact RBCs on microscopy, distinguishing it from true hematuria.
Question 2: A technician performs a reticulocyte count using new methylene blue stain and counts 25 reticulocytes per 1,000 red blood cells. In a patient with a hematocrit of 25%, what is the corrected reticulocyte count (CRC)?
- 0.6%
- 1.1% (Correct answer)
- 2.5%
- 3.3%
Correct answer: 1.1%
The CRC corrects for anemia using the formula: CRC = reticulocyte % Ă— (patient Hct / normal Hct). With 2.5% reticulocytes and Hct of 25% vs. normal 45%: 2.5 Ă— (25/45) = 1.1%. This prevents overestimating erythropoietic activity in anemic patients.
Question 3: Which culture medium is both selective and differential, used to isolate gram-negative enteric organisms while distinguishing lactose fermenters from non-fermenters?
- Blood agar
- Chocolate agar
- MacConkey agar (Correct answer)
- Thayer-Martin agar
Correct answer: MacConkey agar
MacConkey agar contains crystal violet and bile salts that inhibit gram-positive organisms (selective) and lactose with pH indicator neutral red that turns colonies pink-red when lactose is fermented (differential). Non-fermenters such as Salmonella and Shigella appear colorless.
Question 4: A serum protein electrophoresis shows a tall, narrow spike in the gamma region. Which laboratory finding would most support a diagnosis of multiple myeloma?
- Decreased ESR and normal serum calcium
- Bence Jones proteins in urine and rouleaux formation on peripheral smear (Correct answer)
- Elevated serum albumin with polyclonal hypergammaglobulinemia
- Neutrophilia with toxic granulation
Correct answer: Bence Jones proteins in urine and rouleaux formation on peripheral smear
Multiple myeloma is characterized by a monoclonal (M) protein spike, and malignant plasma cells often secrete free immunoglobulin light chains (Bence Jones proteins) detectable in urine. The excess immunoglobulins also cause RBCs to stack (rouleaux), seen on peripheral blood smear.
Question 5: During ABO blood grouping, a patient's red cells react with anti-A but not anti-B, while the patient's serum agglutinates B cells but not A cells. What blood type does this confirm?
- Type O
- Type A (Correct answer)
- Type B
- Type AB
Correct answer: Type A
ABO typing uses forward (cell) and reverse (serum) grouping. Cells reacting with anti-A only indicates A antigen is present. The serum agglutinating B cells confirms the presence of anti-B antibody, consistent with blood type A. Both results must agree before reporting.
Question 6: A chemistry analyzer reports a critically low sodium value of 118 mEq/L on a lipemic sample from a patient. The physician questions the result. Which pre-analytical error most likely accounts for a falsely low sodium by indirect ion-selective electrode (ISE) methodology?
- Specimen hemolysis releasing intracellular sodium
- Pseudohyponatremia due to volume displacement by excess lipids (Correct answer)
- Incorrect reference range for the patient's age group
- Prolonged tourniquet time causing hemoconcentration
Correct answer: Pseudohyponatremia due to volume displacement by excess lipids
Indirect ISE measures sodium in a diluted sample. In severe hyperlipidemia, lipids occupy plasma volume, so the aqueous phase (where sodium actually resides) is underrepresented after dilution, yielding falsely low sodium — pseudohyponatremia. Direct ISE or ultracentrifugation resolves this.
Medical Laboratory Technician Exam ASCP Medical Laboratory Technician 1
A urine specimen tested by dipstick shows a positive result for blood but microscopic examination reveals no red blood cells.
Which condition best explains this discrepancy?