5.1 Special Collections I

Why Special Collections Matters

Special Collections accounts for about 12% of the NHA Certified Phlebotomy Technician (CPT) exam. Although it is the smallest domain by weight, the procedures are high-stakes: a contaminated blood culture can lead to unnecessary antibiotics, a mistimed glucose draw invalidates a diabetes workup, and an alcohol-prepped legal blood alcohol sample can be challenged in court. The exam rewards candidates who know not just how to draw, but the timing and technique details that protect specimen integrity.

Blood Cultures

A blood culture detects bacteria or fungi in the bloodstream (a condition called bacteremia or septicemia). Because even a few skin bacteria can grow in the culture bottle and cause a false positive, skin antisepsis is the single most important step.

Skin Antisepsis and Contamination Prevention

The goal is to reduce normal skin flora at the puncture site to near zero. The widely taught procedure is:

1. Cleanse the site with 70% isopropyl alcohol to remove surface debris and oils.
2. Apply chlorhexidine gluconate (or povidone-iodine for patients sensitive to chlorhexidine) using friction in concentric circles moving outward, or with a back-and-forth scrub per manufacturer instructions.
3. Allow the antiseptic to fully air-dry — typically about 30 seconds of contact time for chlorhexidine, or 1.5-2 minutes for povidone-iodine. Do not fan, blow on, or blot the site.
4. Disinfect the tops of the culture bottles with alcohol and let them dry.
5. Do not re-palpate the cleansed site with an ungloved or non-sterile finger. If you must relocate the vein, re-cleanse.

Order of Bottle Inoculation

A blood culture set is one aerobic bottle plus one anaerobic bottle. The fill order depends on the device used:

• Syringe draw: inoculate the anaerobic bottle... actually, fill the aerobic bottle first. A syringe contains no residual air, so air would not be pushed in; many protocols fill aerobic first to vent.
• Winged (butterfly) set: fill the aerobic bottle first because the tubing is full of air; pushing that air into the anaerobic bottle would compromise the anaerobic environment.

The exam-safe rule to memorize: when air is in the line (butterfly), aerobic goes first. Always follow your facility and CLSI guidance, and never let blood culture bottles overfill — overfilling can cause false positives from white-cell metabolism.

Blood culture bottles are also drawn first in the order of draw because they must be sterile and free of additive carryover. When two sets are ordered (e.g., from two different sites or times), label each with the site and exact time.

Glucose Tolerance Test and Timed Specimens

The glucose tolerance test (GTT) — also called the oral glucose tolerance test (OGTT) — evaluates how the body processes glucose over time and is used to diagnose diabetes and gestational diabetes.

GTT Procedure

1. The patient must fast (typically 8-12 hours; water allowed) before arrival.
2. Draw a fasting baseline glucose specimen.
3. The patient drinks a standardized glucose load — commonly 75 g for a non-pregnant adult (50 g screen or 100 g 3-hour test in obstetric protocols).
4. The clock starts when the patient finishes the drink.
5. Draw additional specimens at scheduled intervals (commonly 1 hour and 2 hours; some protocols add 30 min and 3 hr).
6. Label every tube with the exact draw time and the interval (e.g., "2-hr GTT"). Timing accuracy is critical — an early or late draw produces a clinically misleading curve.

If the patient vomits the glucose drink, notify the provider; the test usually must be rescheduled. Gray-top tubes (sodium fluoride / potassium oxalate) preserve glucose by inhibiting glycolysis and are the standard GTT tube.

Other Timed Specimens

The shared exam principle: timed specimens are only valid if drawn at the ordered time and labeled with the actual collection time.

Therapeutic Drug Monitoring (TDM)

Therapeutic drug monitoring (TDM) measures drug levels in the blood to keep a medication within its safe and effective range. It is essential for narrow-therapeutic-index drugs such as vancomycin, gentamicin, digoxin, lithium, phenytoin, and theophylline.

Peak and Trough

• Trough level — the lowest concentration, drawn immediately before the next scheduled dose. The trough confirms the drug stays above the minimum effective level.
• Peak level — the highest concentration, drawn after absorption is complete. Timing is drug- and route-dependent (often about 1-2 hours after an oral or IV dose; follow the specific protocol).

Because peak and trough results guide dosing, you must record the exact draw time and the time/route of the last dose on the requisition. A mistimed TDM specimen can cause a dangerous dosing error.

Blood Alcohol and Legal (Forensic) Specimens

A blood alcohol concentration (BAC) test — and other legal/forensic draws (drug screens, DUI, employment) — has a special prep rule.

Non-Alcohol Skin Prep

Never use an alcohol-based antiseptic for a blood alcohol draw. Residual isopropyl or ethyl alcohol on the skin can be carried into the specimen and falsely elevate the result. Instead, use a non-alcohol antiseptic such as benzalkonium chloride or aqueous povidone-iodine. Other forensic rules include:

• Use a gray-top tube (sodium fluoride preserves alcohol and inhibits glycolysis).
• Maintain a documented chain of custody (covered in section 5.3).
• Verify patient identity and any required consent per facility and legal policy.
• Fill the tube to the stated volume and invert per additive requirements.