Phlebotomy capillary and dermal puncture practice questions, with every answer explained

1. The thumb of either hand
2. Middle or ring finger
3. The little finger
4. The index finger

Answer: B. The middle or ring finger of the nondominant hand is preferred. The thumb has a pulse, the index finger is often calloused and sensitive, and the little finger has thin tissue over bone.

Why not A: The thumb has a pulse and thick skin.

Why not C: The little finger has little tissue between skin and bone.

Why not D: The index finger is often calloused and more sensitive.

Exam tactic: Middle or ring. Not thumb, index or pinky.

1. Squeeze the finger tightly near the puncture
2. Hold the finger downward and apply gentle, intermittent pressure
3. Raise the hand above the heart
4. Milk the finger hard from base to tip continuously

Answer: B. Holding the finger downward lets gravity help, and gentle pressure that is released between drops lets the capillaries refill.

Why not A: Tight squeezing pushes tissue fluid into the sample and can hemolyze it.

Why not C: Raising the hand reduces flow to the fingertip.

Why not D: Hard continuous milking also adds tissue fluid and hemolysis.

Exam tactic: Point it down, press gently.

1. It is always calloused
2. It has fewer capillaries than the other fingers, so the flow is weak
3. Patients use it less, so it bleeds less
4. Its tissue is thin and the bone is close to the surface

Answer: D. The tissue of the little finger is thin, so the bone is close to the skin and can be injured.

Why not A: Calluses are more typical of the thumb and index finger.

Why not B: The number of capillaries is not the reason.

Why not C: How often a finger is used does not decide bleeding.

Exam tactic: Pinky: too thin.

1. Only after all tubes are collected and labeled at the lab
2. By shaking hard for 10 seconds
3. Never, microtubes do not need mixing
4. Immediately after filling, by gentle inversion per the manufacturer

Answer: D. Microtubes with additives are mixed gently right after filling to prevent microclots, following the manufacturer's instructions.

Why not A: Waiting allows microclots to form.

Why not B: Shaking can hemolyze the sample.

Why not C: Additive microtubes need mixing.

Exam tactic: Fill it, then mix it gently.

1. A patient with very poor peripheral circulation, such as one in shock
2. An adult with good circulation who needs a glucose check
3. A patient with small but healthy fingers
4. A patient who prefers a fingerstick

Answer: A. Skin puncture relies on good flow to the capillaries. In shock, severe dehydration or poor peripheral circulation, capillary results may not reflect the patient's true values.

Why not B: Good circulation makes a fingerstick appropriate.

Why not C: Small fingers can still be used when circulation is good.

Why not D: A preference is fine when the test and circulation allow it.

Exam tactic: Poor circulation, poor capillary sample.

1. Adult lancets are not sterile
2. Adult lancets are too dull to cut through the thicker skin of an infant heel
3. It may puncture too deeply and injure the heel bone
4. It makes the blood clot faster

Answer: C. Lancets are designed for a specific site and depth. An adult finger lancet may go deeper than is safe for an infant heel and can reach the bone.

Why not A: Lancets are sterile, sterility is not the issue.

Why not B: Adult lancets are not dull, they cut too deep, which is the danger.

Why not D: Lancet type does not change clotting speed.

Exam tactic: Right lancet, right depth.

1. They fill faster under the tourniquet
2. They reduce the total blood removed and the risk of iatrogenic anemia
3. They contain no additive and suit all tests
4. Only small tubes fit the pediatric needles and holders used on young children

Answer: B. Children have a small total blood volume. Smaller tubes limit the amount drawn and help prevent anemia caused by repeated sampling.

Why not A: Fill speed is not the reason.

Why not C: Small tubes still contain additives specific to each test.

Why not D: Needle fit is not the reason for smaller tubes.

Exam tactic: Small patient, small tube.

1. It can contaminate the sample and falsely raise some results
2. It is too weak to kill skin bacteria
3. It makes the skin too slippery to puncture
4. It causes the blood to clot instantly

Answer: A. Povidone-iodine can mix into a skin puncture sample and falsely raise results such as potassium, phosphorus, uric acid and bilirubin. 70% isopropyl alcohol is used.

Why not B: Povidone-iodine is an effective antiseptic, strength is not the issue.

Why not C: Slipperiness is not the concern.

Why not D: Iodine does not cause instant clotting.

Exam tactic: Skin puncture: alcohol, not iodine.

1. Hemoglobin
2. Blood culture
3. Newborn screening
4. Blood glucose

Answer: B. Blood cultures need larger volumes collected by venipuncture with sterile technique. Glucose, hemoglobin and newborn screening are commonly done by skin puncture.

Why not A: Hemoglobin can be done by capillary sample.

Why not C: Newborn screening uses heel blood.

Why not D: Glucose is commonly done by fingerstick.

Exam tactic: Blood cultures: venous only.

1. It is too thick to flow into the microtube
2. It may contain excess tissue fluid
3. It contains most of the alcohol-resistant bacteria on the skin and must be cultured separately
4. It always clots before it can be collected

Answer: B. The first drop is more likely to contain tissue fluid, which can dilute the sample. Some point-of-care devices have their own instructions, which are followed.

Why not A: Thickness is not the reason the first drop is removed.

Why not C: The first drop is not sent for culture.

Why not D: The first drop does not always clot.

Exam tactic: First drop out, tissue fluid out.