Phlebotomy blood culture collection practice questions, with every answer explained

1. Extra blood is always better
2. Volume only matters for children's bottles
3. Too little blood causes hemolysis
4. Too little blood lowers the chance of detecting bacteria

Answer: D. Culture sensitivity depends on blood volume; underfilled bottles can miss an infection, while overfilling can raise false positives. Manufacturer volumes are followed.

Why not A: Overfilling can cause problems too.

Why not B: Volume matters for adult and pediatric bottles.

Why not C: Underfilling affects detection, not hemolysis.

Exam tactic: Right volume, better detection.

1. Gray top fluoride
2. Yellow top SPS
3. Lavender top EDTA
4. Gold top SST

Answer: B. Yellow top tubes containing sodium polyanethol sulfonate (SPS) can be used for blood cultures when the lab allows, since SPS inhibits clotting and some antibacterial factors.

Why not A: Fluoride inhibits bacteria and is not for cultures.

Why not C: EDTA is for hematology.

Why not D: SST is for serum chemistry.

Exam tactic: Yellow SPS = culture tube.

1. At bedtime, so the lab receives them in the overnight batch
2. After the first antibiotic dose
3. Only after the fever is gone
4. Before antibiotics are started

Answer: D. Antibiotics can stop bacteria from growing in the culture and cause a false negative. Cultures are drawn before antibiotics whenever possible.

Why not A: Bedtime batching delays diagnosis.

Why not B: Antibiotics in the blood can prevent growth.

Why not C: Waiting until fever resolves can miss bacteria.

Exam tactic: Cultures before antibiotics.

1. It is exactly the same
2. It is much smaller
3. It is double the adult volume
4. Children never get cultures

Answer: B. Pediatric bottles are designed for small volumes, often a few milliliters, based on the child's weight and the manufacturer's guidance.

Why not A: Adult volumes are too large for small children.

Why not C: Children need less, not more.

Why not D: Children do get blood cultures.

Exam tactic: Kids: small-volume culture bottles.

1. Rinse them with tap water and let them air dry
2. Remove the rubber tops
3. Disinfect them per the manufacturer
4. Leave them as shipped

Answer: C. The protective cap is removed and the rubber septum is disinfected, typically with alcohol, per the bottle manufacturer, and allowed to dry.

Why not A: Tap water does not disinfect.

Why not B: The septum stays in place.

Why not D: Tops are not sterile under the cap.

Exam tactic: Disinfect bottle tops too.

1. To tell true infection from skin contamination
2. Because one bottle always breaks
3. To test the blood from each arm for a different blood type
4. To double the billing

Answer: A. Growth of the same organism in sets from different sites supports a true bloodstream infection, while growth in only one set may reflect skin contamination.

Why not B: Breakage is not the reason.

Why not C: A patient has only one blood type; both arms give the same type.

Why not D: Billing is not a clinical reason.

Exam tactic: Two sites: real infection vs contaminant.

1. The aerobic bottle
2. The anaerobic bottle
3. A lavender tube, then the bottles
4. Either, order never matters

Answer: A. With a butterfly set, the aerobic bottle is filled first so the small amount of air in the tubing enters the aerobic bottle instead of the anaerobic one.

Why not B: Air from the tubing would compromise the anaerobic bottle.

Why not C: Culture bottles come before any additive tubes.

Why not D: Order matters with a butterfly because of tubing air.

Exam tactic: Butterfly: aerobic first.

1. So it does not cover the bottle's barcode or the fill volume markings
2. Over the bottle's barcode
3. On the cap
4. Across the bottom of the bottle so the label stays dry and readable in the incubator

Answer: A. The bottle's own barcode and fill markings must stay visible for the instrument and for checking volume. Labels go where the manufacturer and lab direct.

Why not B: Covering the barcode stops the instrument from tracking the bottle.

Why not C: The cap is removed or punctured and is not a labeling surface.

Why not D: Labels on the bottom can interfere with the instrument's reading.

Exam tactic: Don't cover the bottle's barcode.

1. It changes the patient's blood type
2. It only delays the report by an hour
3. It can cause a false positive result, leading to unneeded antibiotics and longer stays
4. It makes the bottle explode

Answer: C. Contaminants can grow and look like a true infection. This can lead to unnecessary treatment, extra tests and longer hospital stays.

Why not A: Blood type is not affected.

Why not B: Contamination has much bigger effects than a short delay.

Why not D: Bottles do not explode from contamination.

Exam tactic: Dirty skin, false positive.

1. The patient's insurance carrier
2. The site of collection and the time drawn
3. The phlebotomist's home phone number
4. The brand of alcohol prep pad and the lot number of the gauze used at the site

Answer: B. Each set is labeled with the collection site and time so the lab and provider can interpret growth, such as a contaminant in only one set.

Why not A: Insurance information is not a specimen requirement.

Why not C: Personal phone numbers never belong on labels.

Why not D: Supply lot details are not part of culture labeling.

Exam tactic: Each set: site and time.