Diagnostic Testing

Diagnostic testing encompasses various procedures used to evaluate patient health. The CMA exam focuses on ECG/EKG, pulmonary function testing, and other common diagnostic procedures that medical assistants assist with or perform.

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Electrocardiography (ECG/EKG)

What Is an ECG?

An electrocardiogram (ECG or EKG) is a non-invasive diagnostic test that records the electrical activity of the heart. It does NOT measure the mechanical pumping action — it measures the electrical impulses that trigger each heartbeat.

Standard 12-Lead ECG Setup

A 12-lead ECG uses 10 electrodes to produce 12 different views of the heart's electrical activity:

Limb Leads (4 electrodes):

Memory aid for limb leads: "White is Right (like snow on the christmas tree)" — start with white on right arm, then go clockwise: white, black, red, green. Or "Smoke (black) over Fire (red)" for the left side.

Precordial/Chest Leads (6 electrodes: V1-V6):

Normal ECG Waveform

Normal Sinus Rhythm Criteria

• Rate: 60-100 beats per minute
• Rhythm: Regular (even spacing between QRS complexes)
• P waves: Present, upright, one before each QRS
• PR interval: 0.12-0.20 seconds, consistent
• QRS complex: <0.12 seconds

Common ECG Abnormalities (Recognition Level)

ECG Artifacts

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Pulmonary Function Testing (PFT)

Spirometry

Spirometry is the most common pulmonary function test, measuring lung volumes and airflow:

Key interpretations:

• Obstructive disease (asthma, COPD): FEV1/FVC ratio decreased (<70%) — air trapping
• Restrictive disease (pulmonary fibrosis): FVC decreased, FEV1/FVC ratio normal or increased
• Reversibility: If FEV1 improves by ≥12% after bronchodilator, suggests asthma (reversible obstruction)

Patient Instructions for Spirometry

1. Sit upright with feet flat on the floor
2. Take the deepest breath possible
3. Place the mouthpiece in the mouth, creating a tight seal
4. Blow out as hard and fast as possible until lungs are completely empty
5. Repeat for at least 3 acceptable attempts (best two within 200 mL of each other)
6. Nose clip may be used to prevent air escape through the nose

Peak Expiratory Flow Rate (PEFR)

• Measures the fastest rate of airflow during forced expiration
• Used primarily for asthma monitoring at home
• Patients establish a personal best when well-controlled
• Green zone (80-100% of personal best): Good control
• Yellow zone (50-80%): Caution — may need medication adjustment
• Red zone (<50%): Medical alert — seek immediate medical attention

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Other Common Diagnostic Tests

Holter Monitor

• Continuous ECG recording for 24-48 hours (or longer with extended monitors)
• Purpose: Detect intermittent arrhythmias not captured on a standard ECG
• Patient wears electrodes and a small recording device during normal daily activities
• Patient keeps a diary of activities, symptoms, and times
• Medical assistant responsibilities: Apply electrodes, instruct patient on diary use, caution about avoiding water/bathing

Vision Screening

• Snellen chart: Standard eye chart for distance visual acuity (read at 20 feet)
• 20/20 vision: Normal visual acuity — can read at 20 feet what a normal eye reads at 20 feet
• 20/40 vision: Patient must be at 20 feet to read what a normal eye reads at 40 feet
• Jaeger chart: Near vision testing (reading at 14-16 inches)
• Ishihara plates: Color vision testing (color blindness screening)

Hearing Screening

• Audiometry: Measures hearing sensitivity at different frequencies and volumes
• Sound measured in decibels (dB) and hertz (Hz)
• Normal hearing: 0-25 dB
• Mild hearing loss: 26-40 dB
• Moderate hearing loss: 41-55 dB
• Tympanometry: Measures middle ear function and eardrum movement

Additional Diagnostic Procedures

Allergy Testing

• Scratch/prick test: Small amounts of allergens are introduced through superficial skin scratches on the forearm or back
• Intradermal test: Small amount injected into the dermis (more sensitive than scratch test)
• Results: Read at 15-20 minutes; a wheal and flare (redness and swelling) indicates a positive reaction
• RAST test: Blood test measuring specific IgE antibodies to allergens (no risk of allergic reaction during testing)
• Patient preparation: Discontinue antihistamines 3-7 days before testing; have epinephrine available in case of anaphylaxis

Radiology (X-Ray) Basics

• Medical assistants may position patients and prepare equipment but do NOT take X-rays unless specifically trained and licensed
• Lead shielding: Always protect reproductive organs and the thyroid when not in the field of view
• Pregnancy: X-rays should be avoided unless medically necessary; always ask females of childbearing age about pregnancy status
• Distance: Operator should stand behind the protective barrier during exposure
• Radiation monitoring: Personnel wear dosimetry badges to track cumulative radiation exposure

Common Lab Panels

Drug Testing (Toxicology)

• Most common specimen: urine (observed or unobserved collection per protocol)
• Chain of custody must be maintained for all forensic/workplace drug testing
• Chain of custody documentation includes: specimen collection time, collector identity, all persons handling the specimen, and secure storage
• Specimens are sealed with tamper-evident tape and signed by the patient and collector
• Confirmatory testing: Immunoassay (screening) followed by GC-MS (gas chromatography-mass spectrometry) for confirmation
• Detection windows: Most drugs detectable in urine for 2-4 days; marijuana may be detectable for up to 30 days in heavy users