Phlebetomy
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phlebotomy procedure definition indications risks authoritative source
Phlebotomy means puncturing a vein with a needle to collect blood. It is most often done for laboratory tests or blood donation.
It can also mean therapeutic phlebotomy, where a controlled amount of blood is removed to lower excess red-cell mass or iron stores, such as in:
- Hereditary hemochromatosis
- Polycythemia vera
- Some cases of porphyria cutanea tarda
Basic venipuncture steps
- Confirm patient identity and explain the procedure.
- Apply a tourniquet and identify a suitable vein, usually the median cubital vein.
- Clean the site and allow it to dry.
- Insert the sterile needle, collect specimens in the required tubes.
- Release tourniquet, withdraw needle, and apply firm pressure.
- Label samples at the bedside and dispose of sharps safely.
Common complications
- Pain, bruising, or hematoma
- Vasovagal dizziness or fainting
- Failed collection or hemolysis of the sample
- Rarely, infection, nerve injury, or prolonged bleeding
For therapeutic phlebotomy, the volume and frequency must be clinician-directed because excessive removal can cause anemia or low blood pressure. Textbook guidance notes that a slower schedule may be required when anemia develops. Yamada's Textbook of Gastroenterology, 7th ed., block 19, lines 1330-1331.
How much blood should draw
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therapeutic phlebotomy standard volume 500 mL patient blood donation volume guidelines
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For therapeutic phlebotomy in an adult, the usual amount is one unit: about 450-500 mL of whole blood, but the exact volume and frequency must be prescribed based on the condition, body size, hemoglobin, blood pressure, and heart/lung status.
- Standard adult amount: 450-500 mL
- Smaller, frail, anemic, or cardiac/pulmonary patients: often 250 mL or another reduced clinician-ordered volume
- Children: commonly weight-based, such as up to 10 mL/kg, with a stated maximum of 500 mL in one pediatric protocol.
- In iron-overload treatment, 500 mL removes roughly 200-250 mg of iron. Therapeutic phlebotomy review
For a routine blood test, only the amount needed for the ordered tubes should be collected, often a few milliliters per tube, not 500 mL.
Do not choose the volume yourself for therapeutic phlebotomy. The order should specify the volume and pre-procedure thresholds such as hemoglobin/hematocrit and blood pressure.
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