ASCP Technologist in Chemistry 2 — Questions and Answers
Question 1: Which electrolyte abnormality is most immediately life-threatening and can cause cardiac arrest?
- Hyponatremia
- Hyperkalemia (Correct answer)
- Hypocalcemia
- Hyperchloremia
Correct answer: Hyperkalemia
Hyperkalemia (elevated potassium) can cause fatal cardiac arrhythmias and cardiac arrest.
Serum potassium above 5.0 mEq/L is dangerous because potassium controls cardiac membrane potential. ECG changes progress with severity: peaked T waves, prolonged PR, widened QRS, and ultimately ventricular fibrillation. Critical values require immediate physician notification. Hemolyzed specimens falsely elevate potassium.
Question 2: What is the clinical significance of elevated troponin levels?
- Liver damage
- Myocardial injury or infarction (Correct answer)
- Kidney failure
- Bone fracture
Correct answer: Myocardial injury or infarction
Cardiac troponin is a highly specific biomarker for myocardial injury and the gold standard for diagnosing acute myocardial infarction.
Cardiac troponins (cTnI and cTnT) are released when myocardial cells are damaged. Troponin rises 3-6 hours after chest pain onset, peaks at 12-24 hours, and remains elevated for 7-14 days. Serial measurements showing a rise and fall pattern are diagnostic. Elevated troponin can also occur in heart failure, myocarditis, PE, and sepsis.
Question 3: Which specimen handling error would falsely elevate serum potassium results?
- Exposing the specimen to light
- Hemolysis of the specimen (Correct answer)
- Refrigerating the specimen
- Using the wrong anticoagulant tube
Correct answer: Hemolysis of the specimen
Hemolysis releases intracellular potassium from red blood cells, which contain about 23 times more potassium than plasma.
Inside RBCs, potassium is approximately 150 mEq/L compared to normal serum of 3.5-5.0 mEq/L. Even mild hemolysis (HI of 50 mg/dL) can increase potassium by approximately 0.5 mEq/L. Causes include small needle gauge, excessive tourniquet time, vigorous mixing, and difficult venipuncture.
Question 4: What does HbA1c measure and over what time period does it reflect glucose control?
- Current blood glucose; past 24 hours
- Glycated hemoglobin; past 2-3 months (Correct answer)
- Fasting insulin levels; past week
- Glucose tolerance; past 6 months
Correct answer: Glycated hemoglobin; past 2-3 months
HbA1c measures the percentage of hemoglobin with glucose attached, reflecting average glucose over 2-3 months (the RBC lifespan).
Glucose non-enzymatically attaches to hemoglobin in proportion to blood glucose concentration. Normal HbA1c is below 5.7%, prediabetes 5.7-6.4%, diabetes 6.5% or higher. Conditions affecting RBC lifespan alter results: hemolytic anemia falsely decreases HbA1c, while iron deficiency falsely increases it.
Question 5: Which liver enzyme is most specific for liver damage?
- AST (aspartate aminotransferase)
- ALT (alanine aminotransferase) (Correct answer)
- Alkaline phosphatase (ALP)
- Gamma-glutamyl transferase (GGT)
Correct answer: ALT (alanine aminotransferase)
ALT is the most liver-specific enzyme because it is found predominantly in hepatocytes, unlike AST which is also found in heart, muscle, and kidneys.
ALT is predominantly in hepatocyte cytoplasm. In hepatitis, ALT is typically higher than AST (ratio > 1). In alcoholic liver disease, AST is often higher (ratio > 2:1, the De Ritis ratio) because alcohol damages mitochondria where mitochondrial AST is concentrated.
Question 6: What specimen type is required for a lipid panel, and what patient preparation is recommended?
- Plasma in a green tube, non-fasting
- Serum in a red or gold tube after 9-12 hours fasting (Correct answer)
- Whole blood in a lavender tube, no fasting
- Capillary blood after 4 hours fasting
Correct answer: Serum in a red or gold tube after 9-12 hours fasting
A lipid panel traditionally requires serum collected after 9-12 hours fasting for accurate triglyceride levels.
Triglycerides are significantly elevated by recent food intake, which also affects calculated LDL (Friedewald equation). Recent guidelines now accept non-fasting panels for initial screening since total cholesterol and HDL are minimally affected. Fasting is still recommended when triglycerides exceed 400 mg/dL.
ASCP Technologist in Chemistry 2
Which electrolyte abnormality is most immediately life-threatening and can cause cardiac arrest?