CMT Clinical Diagnostic Procedures 2 — Questions and Answers
Question 1: When performing a 12-lead ECG, where is lead V1 placed?
- Fourth intercostal space, left sternal border
- Fourth intercostal space, right sternal border (Correct answer)
- Fifth intercostal space, midclavicular line
- Second intercostal space, right sternal border
Correct answer: Fourth intercostal space, right sternal border
Lead V1 is placed at the fourth intercostal space at the right sternal border.
The 12-lead ECG uses 10 electrodes to produce 12 views of the heart's electrical activity. The six precordial (chest) leads are: V1 at the fourth intercostal space, right sternal border; V2 at the fourth intercostal space, left sternal border; V3 midway between V2 and V4; V4 at the fifth intercostal space, left midclavicular line; V5 at the anterior axillary line at the V4 level; and V6 at the midaxillary line at the V4 level.
Question 2: A fasting blood glucose level of 126 mg/dL or higher on two separate occasions indicates:
- Hypoglycemia
- Normal glucose metabolism
- Prediabetes
- Diabetes mellitus (Correct answer)
Correct answer: Diabetes mellitus
A fasting blood glucose of 126 mg/dL or higher on two occasions meets the diagnostic criteria for diabetes mellitus.
According to the American Diabetes Association, diabetes mellitus is diagnosed when fasting plasma glucose is 126 mg/dL or higher on two separate tests, a random glucose is 200 mg/dL or higher with symptoms, a 2-hour oral glucose tolerance test is 200 mg/dL or higher, or HbA1c is 6.5% or higher. Prediabetes is defined as fasting glucose of 100-125 mg/dL. Normal fasting glucose is below 100 mg/dL.
Question 3: Which specimen tube color is used for a complete blood count (CBC)?
- Red top
- Blue top
- Lavender/purple top (Correct answer)
- Green top
Correct answer: Lavender/purple top
Lavender (purple) top tubes contain EDTA anticoagulant, which is required for CBC testing.
Lavender or purple top tubes contain EDTA (ethylenediaminetetraacetic acid), which chelates calcium to prevent clotting while preserving blood cell morphology. EDTA is the anticoagulant of choice for hematology testing including CBC, differential count, and blood smears. Red top tubes (no additive) are for serum chemistry. Blue top tubes (sodium citrate) are for coagulation studies. Green top tubes (heparin) are for stat chemistry and arterial blood gases.
Question 4: What does a pulse oximeter measure?
- Blood pressure
- Heart rate only
- Oxygen saturation of hemoglobin (Correct answer)
- Carbon dioxide levels
Correct answer: Oxygen saturation of hemoglobin
A pulse oximeter uses light absorption to measure the percentage of hemoglobin saturated with oxygen (SpO2).
Pulse oximetry works by passing two wavelengths of light (red at 660nm and infrared at 940nm) through tissue. Oxyhemoglobin absorbs more infrared light while deoxyhemoglobin absorbs more red light. The ratio of absorption at these wavelengths is calculated to determine SpO2. Normal SpO2 is 95-100%. Readings can be inaccurate with poor perfusion, nail polish, carbon monoxide poisoning, severe anemia, or excessive movement.
Question 5: When collecting a clean-catch midstream urine specimen, the patient should:
- Collect the first portion of urine
- Begin voiding, then collect the midstream portion (Correct answer)
- Collect urine over a 24-hour period
- Use a catheter for all specimens
Correct answer: Begin voiding, then collect the midstream portion
A clean-catch midstream specimen requires the patient to begin voiding to flush urethral bacteria, then collect the middle portion.
The clean-catch midstream technique minimizes contamination from urethral flora. The patient first cleanses the periurethral area with antiseptic wipes, begins voiding into the toilet to flush bacteria from the distal urethra, then collects the midstream portion in a sterile container without stopping the flow. The last portion is voided into the toilet. This technique reduces false-positive culture results and is standard for routine urinalysis and urine cultures.
Question 6: An abnormally low platelet count is termed:
- Leukopenia
- Thrombocytopenia (Correct answer)
- Anemia
- Neutropenia
Correct answer: Thrombocytopenia
Thrombocytopenia refers to a platelet count below the normal range, typically under 150,000/μL.
Thrombocytopenia is defined as a platelet count below 150,000/μL. Causes include decreased production (bone marrow failure, chemotherapy), increased destruction (immune thrombocytopenic purpura, heparin-induced thrombocytopenia), or sequestration (splenomegaly). Spontaneous bleeding risk increases significantly when counts fall below 20,000/μL. Leukopenia refers to low white blood cells, anemia to low red blood cells or hemoglobin, and neutropenia specifically to low neutrophils.
CMT Clinical Diagnostic Procedures 2
When performing a 12-lead ECG, where is lead V1 placed?