3.2 Site Selection

3.2 Site Selection

Quick Answer: First choice for adult venipuncture is usually the median cubital vein, then cephalic, with basilic last due to nerve/artery proximity. Use hand veins when needed. Avoid fistula/graft arms, ipsilateral mastectomy/lymphedema, hematoma, infection, heavy scarring, and draws above running IVs. Capillary sites: lateral finger pads; infant medial/lateral plantar heel. Never collect from the underside of the wrist.

Site selection is a patient-safety skill as much as a technical one. The “best” vein is not always the most visible—it is the vessel that can be entered with the lowest risk of nerve injury, arterial puncture, specimen contamination, and limb complications.

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Preferred Venipuncture Region: Antecubital Fossa

The antecubital fossa (inside of the elbow) is the primary adult site. Superficial veins here are often large, stable, and easy to compress after the draw.

Vein priority (exam-critical)

H-pattern vs M-pattern vein layouts vary by person; always palpate, do not rely on a textbook diagram of the patient’s arm. A good vein feels elastic and bouncy, is non-pulsatile, and has a predictable path.

Palpation habits that protect patients

• Use the index finger pad, not the thumb (thumb has its own pulse).
• Trace direction and depth; estimate gauge needs.
• If you feel a pulse, you are on or near an artery—do not stick there.
• Hard cord-like structures may be tendons or nerves—do not puncture what does not feel venous.

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Hand and Other Alternative Venous Sites

When antecubital veins are sclerosed, scarred, used for IV access, or otherwise unsuitable:

• Dorsal hand veins are common alternatives. Use a smaller needle or butterfly, anchor carefully (hand veins roll), and expect slightly more patient discomfort.
• Wrist veins on the dorsal aspect may be used with caution and experience; avoid blind deep sticks.
• Ankle/foot veins are restricted in many facilities (diabetes, poor perfusion, clot risk) and often require provider approval—know local policy before using them.
• Never use the ventral (palm-side) wrist/forearm where nerves and tendons are dense—the classic teaching is do not draw from the underside of the wrist.

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Sites and Situations to Avoid

IV therapy arm

IV fluids and medications dilute or contaminate specimens (e.g., spuriously high glucose with dextrose infusions, altered electrolytes).

Hierarchy of preference:

1. Draw from the other arm if possible.
2. If both arms have IVs or only one arm is available: work distal to (below) the IV, after nursing pauses the infusion per policy (commonly a few minutes), and follow discard-volume rules when required.
3. Do not draw above (proximal to) an active IV.
4. Do not draw from the IV line itself unless you are specifically trained and authorized for line draws.

Mastectomy, lymphedema, and nodal dissection

Avoid the ipsilateral arm. Lymphedema risk and infection risk are the drivers. Bilateral restrictions → escalate for an approved plan (see Section 3.1).

Fistula or graft

No tourniquet, no venipuncture, no blood pressure cuff on the access arm. Protect the dialysis access at all costs.

Hematoma

Do not stick through a hematoma. Results may be hemolyzed or contaminated with extravascular blood, and the patient will have unnecessary pain. Choose another site distal or on the other arm.

Infection, inflammation, phlebitis

Avoid erythematous, purulent, or inflamed areas. Breaking the skin through infection can seed deeper tissue and contaminates cultures.

Extensive scarring, burns, tattoos (relative), edema

Heavy scar tissue is hard to puncture and may have poor flow. Fresh burns are off-limits. Extensive tattoos are not an absolute ban but can obscure veins and, if freshly inked/infected, should be avoided—prefer non-tattooed skin when possible. Edematous tissue dilutes specimens and hides landmarks.

Arterial lines and special devices

Routine venous specimens are not drawn from arterial lines by untrained staff. PICC/central line sampling follows nursing protocols, not casual MLA practice.

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Capillary (Skin Puncture) Sites

Capillary collection is used for infants, some point-of-care tests, limited volumes, or when venous access is not appropriate for the ordered test menu.

Fingerstick (older children and adults)

• Prefer the palmar surface of the distal phalanx, lateral aspects of the 3rd or 4th finger (middle or ring finger).
• Avoid the index finger (calluses, thicker skin) and 5th finger (insufficient tissue) when better options exist; avoid the thumb.
• Do not puncture the extreme tip or the very center of the finger pad where bone injury risk is higher.
• Warm the hand if needed; wipe away the first drop when policy/test requires (tissue fluid contamination).
• Do not “milk” aggressively—excessive squeezing increases hemolysis and tissue-fluid dilution.

Infant heel stick

• Use the medial or lateral plantar surface of the heel (shaded safe zones on standard diagrams).
• Avoid the posterior curvature of the heel (bone/osteomyelitis risk) and avoid fingers/toes for routine newborn screening collections when heel is indicated.
• Depth-controlled lancets reduce calcaneal injury risk—use age-appropriate devices only.
• Warm the heel to improve flow; follow newborn screening and blood gas capillary protocols exactly when those tests are ordered.

Capillary vs venous decision

Not every test is valid on capillary blood (many coag tests and blood bank specimens require venous anticoagulated samples). When the order demands venous or arterial blood, do not substitute a fingerstick without laboratory approval.

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Skin Preparation Tied to Site

Once the site is chosen:

1. Cleanse with 70% isopropyl alcohol (or facility-approved antiseptic; blood cultures may require chlorhexidine or iodine per protocol).
2. Use friction; allow complete air drying—do not recontaminate by touching the site or fanning with a dirty glove.
3. For blood cultures, follow full sterile prep and bottle order rules (Section 3.3).

Site selection and antisepsis work together: a perfect vein with a wet alcohol field still risks hemolysis and stinging, and a culture site touched after prep is a contaminated culture.

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Scenario Patterns Common on MLA Items

• Obese patient, deep veins: cephalic may be easiest; longer needle only if trained/available; do not dig blindly medially toward basilic structures.
• Chemotherapy patient, sclerosed antecubitals: hand veins with butterfly; gentle vacuum.
• Patient with left AV fistula and right-hand IV: coordinate with nursing—often distal right hand/forearm after IV pause, or escalate.
• Toddler needing limited labs: fingerstick if tests allow; otherwise pediatric butterfly with helper to stabilize.
• Newborn screen: proper heel zones and completely filled circles on filter paper (processing details appear in later chapters).

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Linking Site Choice to Later Steps

A correct site still fails if order of draw is wrong or tubes are underfilled. After site selection, execute collection with controlled angle (commonly about 15–30° for antecubital ETS), steady anchoring, and immediate tube mixing. Label at the bedside. Adverse events (syncope, nerve injury symptoms, arterial puncture) are covered in Chapter 4—but many are prevented by refusing high-risk sites.

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Key Takeaways

• Median cubital → cephalic → basilic (caution) is the standard adult priority.
• Protect restricted limbs: mastectomy side, fistula, IV proximal draws, hematoma, infection.
• Capillary: lateral finger; infant medial/lateral plantar heel.
• Never the underside of the wrist; when no safe site exists, stop and escalate.