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Clinical Procedures: Injections, EKG, Phlebotomy, and Instrument Processing

This domain covers the hands-on procedures a medical assistant performs every day, from giving an intramuscular injection to running a twelve-lead EKG and drawing a full tube set in the correct order. Angles, gauges, lead positions, and tube sequences are memorization-heavy, so build a mental table for each one.

Injections: intradermal, subcutaneous, and intramuscular

Each parenteral route has its own needle gauge, needle length, insertion angle, maximum volume, and set of approved sites. Choose the site based on the medication, the volume, and the patient's muscle mass, and always aspirate-free technique per current vaccine guidance. Never recap a used needle; activate the safety device and drop it into the sharps container at the point of use.

Intradermal injection
Insert at a 10 to 15 degree angle with the bevel up, using a 25 to 27 gauge needle three-eighths to five-eighths inch long and a volume of about 0.1 mL into the inner forearm. A raised wheal confirms correct placement; a tuberculin skin test is read at 48 to 72 hours.
CDC
Subcutaneous injection
Insert at a 45 degree angle, or 90 degrees with a short needle in a pinched skin fold, using a 25 to 27 gauge needle three-eighths to five-eighths inch long and no more than about 1 mL. Common sites are the abdomen, the upper outer arm, and the anterior thigh.
CDC
Intramuscular injection
Insert at a 90 degree angle with a 22 to 25 gauge needle one to one and a half inches long. Adult deltoid volume is usually limited to 1 mL, while larger muscles such as the ventrogluteal and vastus lateralis tolerate up to 3 mL.
CDC
Site selection by patient
The vastus lateralis is the site of choice for infants, the deltoid is used for most adult vaccines, and the ventrogluteal is preferred for large or irritating volumes in adults. The dorsogluteal site is avoided because of sciatic nerve risk.
Z-track technique
Pull the skin laterally before inserting the needle, inject, wait about ten seconds, withdraw, then release the skin so the tissue layers seal the tract. This prevents irritating medication such as iron dextran from leaking into subcutaneous tissue and staining the skin.
Sharps safety at the point of care
Do not recap, bend, shear, or break used needles. Activate the engineered sharps injury protection device and dispose of the whole unit in a closable, puncture-resistant, labeled sharps container immediately.
OSHA 29 CFR 1910.1030

The rights of medication administration

The rights framework is a checklist that prevents the most common and most dangerous medication errors. Verify each right at three separate points: when you take the container, when you prepare the dose, and before you administer or return the container. Medical assistants administer only what a supervising provider has ordered and only within their state scope.

The core six rights
Right patient, right drug, right dose, right route, right time, and right documentation. Documentation is a right because an unrecorded dose can lead to a duplicate dose.
The added rights
Modern practice adds the right reason or indication, the right patient education, the right assessment before administration, the right to refuse, and the right response or evaluation afterward.
Three checks of the label
Read the medication label when you remove it from storage, when you draw up or pour the dose, and again before you administer it or return the container to the shelf.
Never give what you did not prepare
Do not administer a medication drawn up by someone else, and never give a dose from an unlabeled, illegible, expired, discolored, or cloudy container. When in doubt, discard it and start over.
Verify allergies before every dose
Ask the patient about allergies and check the chart even when the record already lists them, because new allergies develop and patients often remember reactions at the last moment.
Document immediately after, never before
Chart the drug, dose, route, site, time, lot number and expiration for vaccines, and the patient's response right after administration. Charting in advance is falsification of the record.

Electrocardiography and lead placement

A standard twelve-lead EKG uses four limb electrodes and six chest electrodes to record the heart's electrical activity from twelve angles. Correct chest lead placement is the difference between a readable tracing and a false abnormality. The medical assistant records the tracing and reports obvious life-threatening rhythms immediately, but does not interpret or diagnose.

Chest lead positions V1 through V3
V1 sits in the fourth intercostal space at the right sternal border, V2 in the fourth intercostal space at the left sternal border, and V3 midway between V2 and V4.
American Heart Association
Chest lead positions V4 through V6
V4 sits in the fifth intercostal space at the midclavicular line, V5 at the anterior axillary line level with V4, and V6 at the midaxillary line level with V4 and V5.
American Heart Association
Limb lead placement and color code
Place limb electrodes on fleshy areas of all four limbs, avoiding bone. The common memory aid is white on the right arm, black on the left arm, red on the left leg, and green on the right leg, or white on right and smoke over fire.
Standard calibration
Standard paper speed is 25 millimeters per second and standard sensitivity is 10 millimeters per millivolt. One small box equals 0.04 second and one large box equals 0.20 second.
Recognizing artifact
Somatic tremor produces jagged irregular spikes from muscle movement or shivering, wandering baseline comes from loose electrodes, lotion, or respiration, and alternating current interference shows uniform small spikes from nearby electrical equipment.
Skin preparation
Clean the site with alcohol and let it dry, gently abrade dry or oily skin, and clip rather than shave excess hair. Poor skin contact is the most common cause of a poor-quality tracing.

Phlebotomy: order of draw and specimen handling

The order of draw exists to prevent additive carryover between tubes, which can invalidate results. Follow it exactly, mix additive tubes by gentle inversion, and label every tube in front of the patient before you leave the room. Hemolysis and short draws are the two most common reasons a laboratory rejects a specimen.

Order of draw
Draw blood culture bottles or yellow SPS tubes first, then light blue sodium citrate, then red or gold serum tubes, then green heparin, then lavender EDTA, and finally gray sodium fluoride and potassium oxalate.
CLSI GP41
Tourniquet time
Leave the tourniquet on for no more than one minute. Prolonged application causes hemoconcentration, which falsely elevates results such as potassium, protein, and packed cell volume.
Vein selection
The median cubital vein is the first choice, followed by the cephalic and then the basilic vein, which sits near the brachial artery and median nerve. Avoid the arm on the side of a mastectomy, an arm with an active IV above the site, and areas with hematoma, scarring, or edema.
Mix, do not shake
Invert additive tubes gently three to eight times per manufacturer instructions immediately after collection. Vigorous shaking causes hemolysis, and no mixing causes clotting in anticoagulant tubes.
Hemolysis changes results
Hemolyzed specimens falsely elevate potassium, magnesium, phosphorus, and certain enzymes because these leak out of ruptured red cells. Common causes are a needle that is too small, vigorous shaking, and forcing blood through a needle into a tube.
Coagulation tube fill requirement
A light blue citrate tube must be filled completely to maintain the nine parts blood to one part anticoagulant ratio. A short-draw blue tube is rejected because it falsely prolongs clotting times.

Point-of-care testing, sterilization, and the autoclave

Medical assistants run waived tests in the office and process the instruments used in minor procedures. Waived testing still requires quality control, documentation, and following the package insert exactly. Instrument processing always moves in the same order: sanitize, then disinfect or sterilize according to how the instrument will be used.

Common CLIA-waived tests
Waived tests include blood glucose meters, urine dipsticks, urine pregnancy tests, rapid strep, rapid influenza, hemoglobin, and fecal occult blood. A facility must hold at least a Certificate of Waiver to perform them.
CLIA 42 CFR Part 493
Quality control is mandatory
Run and log controls at the frequency the manufacturer specifies, and do not report patient results if a control falls outside its acceptable range. Correct the problem, repeat the control, and document what you did.
Sanitization, disinfection, sterilization
Sanitization removes visible soil, disinfection destroys most microorganisms on surfaces, and sterilization destroys all microorganisms including bacterial spores. Instruments entering sterile tissue or the vascular system must be sterilized.
CDC
Autoclave parameters
A standard gravity-displacement cycle runs at 250 degrees F (121 degrees C) at 15 pounds per square inch for roughly 20 to 30 minutes, with longer times for wrapped packs. It is the steam under pressure, not the heat alone, that sterilizes.
CDC
Loading the autoclave
Load packs on edge with space between them so steam circulates, do not overcrowd the chamber, place containers on their side, and open hinged instruments before wrapping. Trapped air and crowding are the main causes of sterilization failure.
Monitoring and pack labeling
Use a chemical indicator on or in every pack and run a biological spore test with Geobacillus stearothermophilus at least weekly. Label each pack with contents, sterilization date, and your initials, and treat any wet, torn, or dropped pack as contaminated.
CDC
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Last updated: July 2026

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