Tourniquet Use in Phlebotomy

How Tourniquets Work

When properly applied, a tourniquet compresses superficial veins but not the deeper brachial artery. Arterial blood continues to flow into the arm, but venous blood cannot flow out as easily. This causes veins distal to (below) the tourniquet to fill with blood and become distended, firm, and visible under the skin.

• Makes veins visible: Engorged veins are easier to see, especially in patients with deep or small veins
• Makes veins palpable: Distended veins feel firm and springy when palpated, confirming they are veins (not arteries or tendons)
• Anchors veins: Full veins are less likely to roll or collapse during needle insertion
• Increases blood flow into collection tubes: Elevated venous pressure makes blood flow more readily into evacuated tubes

1. Select Proper Tourniquet Type

Use a flat latex band (most common), Velcro strap tourniquet, or non-latex alternative for patients with latex allergies. Tourniquets should be clean and non-porous (or single-use disposable) to prevent cross-contamination between patients. Never use tubing, rope, or improvised materials.

2. Position Tourniquet 3-4 Inches Above Venipuncture Site

Place the tourniquet 3-4 inches (7-10 cm) above the intended venipuncture site — typically 3-4 inches above the antecubital fossa (elbow crease). This distance allows optimal vein engorgement in the collection area without causing discomfort in the upper arm. The tourniquet should lie flat against the skin without twists.

3. Apply with Appropriate Tightness

Wrap the tourniquet snugly but not painfully tight. Proper pressure is 40-60 mmHg — tight enough to restrict venous flow but not arterial flow. The patient should feel pressure but not pain, tingling, or numbness. For standard latex tourniquets, create a half-bow knot (like tying a shoe) so it can be quickly released with one hand.

4. Verify Proper Application

After applying the tourniquet, check for: (1) distal radial pulse still palpable (if not, loosen tourniquet), (2) veins beginning to engorge within 15-30 seconds, (3) patient reports pressure but not pain or numbness, (4) tourniquet ends tucked away from venipuncture site to avoid contamination.

5. Tuck Free Ends Away from Site

Tuck the free ends of the tourniquet upward and away from the venipuncture site so they do not dangle into the sterile field. Dangling ends can brush against the needle, puncture site, or collection tubes and cause contamination.

Why the 1-Minute Limit Exists: Hemoconcentration

Prolonged tourniquet application causes hemoconcentration — a condition where blood cells and large molecules become abnormally concentrated in the blood due to fluid leaking from the blood into surrounding tissues. This happens because the tourniquet increases capillary permeability and hydrostatic pressure, forcing plasma water and small molecules out of the blood vessels while retaining larger molecules and cells.

Tests Affected by Hemoconcentration (Falsely Elevated):

• Total protein and albumin: Large molecules retained in blood
• Enzymes (AST, ALT, LDH, CK): Large molecules concentrated
• Lipids (cholesterol, triglycerides): Large lipoproteins retained
• Calcium and potassium: Released from cells and concentrated
• Red blood cells, white blood cells, platelets: Cells concentrated in specimen
• Coagulation factors: Prolonged tourniquet activates coagulation cascade

Other Consequences of Prolonged Tourniquet Use

• Hemolysis: Red blood cells rupture due to pressure and hypoxia, invalidating potassium, LDH, AST, and many other tests
• Petechiae: Small red dots from broken capillaries, causing patient alarm and cosmetic concern
• Patient discomfort: Pain, numbness, tingling in the arm
• Nerve compression injury: In extreme cases (over 3 minutes), can cause temporary or permanent nerve damage
• Thrombosis risk: Stasis of blood increases clot formation risk

Above IV Site or Fistula

Never apply a tourniquet: On an arm with an IV line (causes IV fluid to back up and dilute specimen), on an arm with a dialysis fistula or graft (can damage the access site or cause thrombosis), on an arm affected by mastectomy or lymphedema (increases lymphatic pressure).

Hand Veins with Fragile Skin

When drawing from hand veins in elderly patients or patients with fragile skin, use a blood pressure cuff inflated to 40-60 mmHg instead of a standard tourniquet. The cuff distributes pressure more evenly and is less likely to cause skin tears or bruising.

Coagulation Studies (PT/PTT) — Special Considerations

For coagulation studies, some facilities require using a tourniquet only long enough to locate the vein, then releasing it before needle insertion, or using no tourniquet at all (if vein is easily visible). Prolonged tourniquet use can activate coagulation factors and affect PT/PTT results. Always follow your facility's specific protocol.

Lactic Acid and Ammonia Tests

Lactic acid levels can be falsely elevated by tourniquet use (muscle cell anaerobic metabolism produces lactate). For lactic acid tests, use minimal tourniquet time (under 30 seconds) or no tourniquet if possible. Ammonia tests are also affected by prolonged tourniquet use and muscle activity.

Burns, Rashes, or Open Wounds

Do not place a tourniquet over burned skin, rashes, open wounds, or areas with infections. The tourniquet can cause pain, further tissue damage, and contamination. Select an alternate site or alternate arm.

When to Use a BP Cuff Instead of a Tourniquet

• Elderly patients with fragile skin: Even pressure reduces risk of skin tears and bruising
• Obese patients: Difficult to achieve proper tourniquet tightness with standard bands
• When standard tourniquet fails: Some patients' veins do not engorge with standard tourniquets
• Tests requiring precise pressure control: Can set exact mmHg pressure

High-Yield Exam Topics

• Maximum tourniquet time: 1 minute (60 seconds) from application to needle removal
• Tourniquet must be released BEFORE needle removal to prevent hematoma
• Proper placement: 3-4 inches above venipuncture site
• Hemoconcentration: causes falsely elevated results for proteins, enzymes, lipids, calcium, potassium
• Proper tightness: restrict venous flow but not arterial flow (check distal pulse)
• Never place tourniquet on arm with IV, fistula, mastectomy, or lymphedema
• Blood pressure cuff alternative: inflate to 40-60 mmHg (midpoint between diastolic and systolic)
• If venipuncture takes longer than 1 minute: release tourniquet, wait 2 minutes, reapply, proceed immediately

How long should a tourniquet be left on during venipuncture?

A tourniquet should remain on for no longer than 1 minute (60 seconds) from application to needle withdrawal. Prolonged tourniquet application causes hemoconcentration — blood cells and large molecules become concentrated due to fluid leaking into tissues, resulting in falsely elevated test results for proteins, enzymes, cholesterol, potassium, and coagulation factors. If venipuncture takes longer than 1 minute, release the tourniquet, wait 2 minutes for circulation to normalize, then reapply and reattempt.

What happens if you leave a tourniquet on too long?

Leaving a tourniquet on longer than 1 minute causes hemoconcentration (falsely elevated results for total protein, enzymes, cholesterol, calcium, potassium), hemolysis (ruptured red blood cells invalidating many tests), petechiae (small red spots from broken capillaries), and patient discomfort or nerve compression. In extreme cases (over 3 minutes), it can cause thrombosis or permanent nerve damage. Always monitor tourniquet time carefully.

Should you release the tourniquet before or after needle removal?

Release the tourniquet BEFORE removing the needle — this is critical for patient safety. The correct sequence is: (1) fill the last tube, (2) remove the last tube from the holder, (3) release the tourniquet, (4) place gauze over the puncture site, (5) remove the needle. If you remove the needle while the tourniquet is still on, blood pressure in the vein is elevated and will cause excessive bleeding and hematoma formation.

How tight should a tourniquet be applied?

A tourniquet should be snug enough to restrict venous blood flow (making veins bulge) but not so tight that it occludes arterial blood flow. You should still be able to palpate a distal pulse (radial pulse at the wrist). If you cannot feel a pulse, the tourniquet is too tight — loosen it immediately. The patient should feel pressure but not severe pain or numbness. Proper tightness is 40-60 mmHg (between diastolic and systolic blood pressure).

Where should the tourniquet be placed on the arm?

Place the tourniquet 3-4 inches (7-10 cm) above the intended venipuncture site — typically 3-4 inches above the antecubital fossa (elbow crease). This location is high enough to engorge veins in the antecubital area without causing discomfort in the upper arm. Never place a tourniquet directly over the puncture site, over broken skin, over an IV site, or on an arm with a dialysis fistula, mastectomy, or lymphedema.

Can you use a blood pressure cuff instead of a tourniquet?

Yes — a blood pressure cuff can be used as a tourniquet by inflating it to 40-60 mmHg (midway between the patient's diastolic and systolic blood pressure). This provides more controlled, even pressure than a standard latex or Velcro tourniquet and is especially useful for patients with fragile skin, the elderly, or when standard tourniquets fail to engorge veins. However, it is slower to apply and release, so it is not routinely used unless medically indicated.