Phlebotomy 101: Technical Aspects

Butterfly Needles vs Straight Needles

Phlebotomists often have to choose between winged infusion sets (WIS), more commonly referred to as butterfly needles, and straight needles for blood collection. Both have their own advantages and disadvantages depending on the patient and the situation.

Straight Needles:

• Ideal for: Drawing larger blood volumes; accessing larger veins; situations where stability is crucial.

• Benefits: Provides a more stable connection for blood collection, is generally more cost-effective.

• Considerations: May be more difficult to use on small or rolling veins, potentially causing more discomfort.

Butterfly Needles:

• Ideal for: Small, fragile, or rolling veins, particularly in the hands or feet; pediatric patients; situations requiring greater maneuverability.

• Benefits: Increased control and maneuverability, often resulting in less pain for the patient, has a built-in needle safety device.

• Considerations: Can be less stable than straight needles, potentially increasing the risk of dislodgement.

The Best Choice:

The choice of needle ultimately depends on the individual patient's needs and the phlebotomist's professional judgment. Factors such as the patient's age, vein condition, and the amount of blood required should all be considered when making this decision.

Needle Gauges

Choosing the right gauge is crucial for phlebotomists, impacting the patient's comfort, sample quality, and overall success of the procedure. Smaller gauge needles (higher numbers) are gentler on fragile veins, children, the elderly, or  patients with difficult veins, minimizing pain and bruising. However, they may not be suitable for faster blood flow but can cause more discomfort. Selecting the appropriate gauge ensures sufficient blood flow for tests while prioritizing patient comfort and minimizing complications like hemolysis (red blood cell rupture) from using a needle too small. 

Capillary Punctures

Capillary puncture is a common procedure used to collect small blood samples by pricking the skin, usually on the fingertip, heel, or earlobe. This method accesses blood from the capillaries, tiny blood vessels located near the skin's surface.

Capillaries and Blood Types:

Capillaries are the smallest blood vessels in the body, forming a vast network that connects arteries (carrying blood away from the heart) to veins (carrying blood back to the heart). Capillary blood is a mixture of blood from arterioles, venules, and tissue fluids. While capillary blood can be used for many tests, since capillaries are a mixture of venous and arteriole blood, there can be slight differences in results compared to venous blood. Capillary blood may show slightly higher levels of hemoglobin and hematocrit due to the squeezing action during collection. Minor variations can also occur in other analytes like glucose, potassium, and calcium. However, some tests are not suitable for capillary blood, such as blood cultures, certain coagulation studies, and blood gas analysis. 

• Capillary Blood: A mixture of blood from arterioles, venules, and tissue fluids.

• Venous Blood: Deoxygenated blood returning to the heart.

• Arterial Blood: Oxygenated blood pumped from the heart.  

When is Capillary Puncture Used?

• Infants and Children: Capillary punctures are often the preferred method for obtaining blood samples from infants and young children when venipuncture (drawing blood from a vein) may be difficult or traumatic.

• Point-of-Care Testing: Many point-of-care tests, such as blood glucose monitoring, utilize capillary blood samples for quick and convenient results.

• Limited Blood Volume: When only a small amount of blood is required for testing.

When is Capillary Puncture NOT Used?

• Tests Requiring Large Blood Volumes: Venipuncture is generally preferred for tests that require larger blood volumes.

• Certain Laboratory Tests: Some specific laboratory tests may require venous blood for accurate results.

• Easily Accessible Veins: If a vein is easily accessible, venipuncture is often the more efficient method.

The Capillary Puncture Procedure:

A small, sterile device called a lancet is used to make a quick, shallow prick in the skin. The depth of the puncture is usually adjustable to minimize discomfort and the risk of injury.

Capillary Puncture in Infants:

Capillary punctures in infants are typically performed on the heel. Techniques such as warming the heel and using a vibrating device can help minimize discomfort.

PKU Screening:

Phenylketonuria (PKU) is a genetic disorder that requires early detection and treatment. In most regions, newborn screening for PKU is mandatory. This involves collecting a small blood sample from the infant's heel and placing it on a special card for analysis.