Phlebotomy
Phlebotomy is the medical procedure involving the puncture of a vein, typically in the arm, to withdraw blood from a patient using a needle and collection system, primarily for diagnostic laboratory testing, blood donation, or therapeutic removal of excess blood volume. The term phlebotomy derives from Ancient Greek φλεβοτομία (phlebotomía), from φλέψ (phleps, "vein") + the suffix -τομία (-tomía, "cutting").[1][2] The origins of phlebotomy date back over 3,000 years to ancient Egyptian practices of bloodletting, where it was employed to treat ailments by removing what was believed to be impure blood, a concept later expanded by Greek physicians like Hippocrates and Galen under the theory of balancing the four humors.[3] This historical therapeutic approach persisted through Roman, Arab, and medieval European medicine but declined in the 19th century with advances in scientific understanding of disease, shifting phlebotomy's focus toward diagnostic and supportive roles in modern healthcare.[4] In contemporary practice, phlebotomy is a foundational element of clinical diagnostics, enabling the analysis of blood components to detect infections, monitor chronic conditions, and guide treatments, with laboratory results influencing approximately 70% of medical decisions.[5] Performed by certified phlebotomy technicians who undergo specialized training in venipuncture techniques, patient interaction, and safety protocols, the procedure emphasizes sterile conditions to prevent complications like infection or hemolysis.[6] Therapeutic applications remain relevant for managing disorders such as polycythemia vera, hemochromatosis, and porphyria cutanea tarda by reducing elevated red blood cell counts or iron levels.[7]Definition and Etymology
Definition
Phlebotomy is a medical procedure involving the puncture of a vein, typically using a needle or cannula, to withdraw blood from the circulatory system for various clinical purposes. This process, known as venipuncture, allows for the collection of blood samples in a controlled manner to support healthcare diagnostics and treatments.[1][8] Unlike historical venesection, which encompassed broader bloodletting practices often performed without sterile conditions to balance bodily humors, modern phlebotomy adheres to rigorous aseptic techniques to minimize infection risks and ensure patient safety. It focuses specifically on precise vein puncture rather than indiscriminate blood removal.[9][1] The term derives from the Greek roots phlebo- meaning "vein" and -tomy meaning "cutting."[1][10]Etymology
The term "phlebotomy" derives from the Ancient Greek φλεβοτομία (phlebotomía), a compound of φλέψ (phleps, meaning "vein") and the suffix -τομία (-tomía, from τέμνειν [témnein], meaning "to cut" or "incision"), literally signifying "vein-cutting" or "opening of a vein."[2] This etymological root reflects the procedure's historical association with incising veins to release blood.[11] The word entered English in the 14th century, with the earliest known uses appearing before 1400 in Middle English texts, often in the context of medieval bloodletting practices.[12] It was borrowed via Old French flebothomie (modern French phlébotomie) and Late Latin phlebotomia, adapting the Greek term for medical writings on therapeutic venesection.[13] Related terms include "venesection," a synonym derived from Latin vena ("vein") + sectio ("cutting"), first recorded in English in 1661 and emphasizing the surgical aspect of vein incision.[14] In medical literature, the terminology evolved from its attestation in ancient Greek texts, such as those of the Hippocratic Corpus, where it described bloodletting techniques, through Roman and medieval Latin adaptations, to its modern usage denoting precise venipuncture for diagnostic or therapeutic purposes.[15]Purposes
Diagnostic Phlebotomy
Diagnostic phlebotomy serves as the primary method for obtaining venous blood samples to facilitate laboratory-based medical diagnosis, allowing healthcare providers to evaluate a patient's health through various analyses. Common tests supported by this procedure include the complete blood count (CBC), which measures red and white blood cell counts, hemoglobin levels, and platelets to detect conditions like anemia or infection; chemistry panels, assessing electrolytes, glucose, liver enzymes, and kidney function markers; and microbiology cultures, such as blood cultures that identify pathogens like bacteria or fungi in cases of suspected sepsis.[16][17][18] These analyses provide critical insights into organ function, metabolic status, and infectious diseases, guiding treatment decisions across clinical settings. The volume of blood drawn in diagnostic phlebotomy is carefully controlled to ensure patient safety while meeting test requirements. Standard evacuated collection tubes typically accommodate 2 to 10 mL of blood per tube, with the exact volume varying by tube type and additive for specific assays, such as smaller volumes for pediatric or coagulation tests. Total draws are limited to no more than 5% of the patient's estimated total blood volume (approximately 70 mL/kg in adults) within a 24-hour period to prevent complications like iatrogenic anemia, especially in hospitalized or pediatric patients.[19][20][21] Venipuncture for diagnostic purposes most commonly targets the superficial veins of the antecubital fossa due to their prominence and ease of access, specifically the median cubital vein (preferred for its stability and central location), the cephalic vein (lateral and often visible), and the basilic vein (medial, used when others are unsuitable). These sites are selected to optimize blood flow and minimize patient discomfort while yielding sufficient sample quality.[22][23] Integration with laboratory workflows emphasizes preserving sample integrity from collection to analysis, as errors can compromise diagnostic accuracy. Phlebotomists must employ techniques to prevent hemolysis—the rupture of erythrocytes that releases intracellular contents and interferes with potassium, LDH, and other assays—and avoid contamination from improper skin preparation or equipment handling, which could introduce microbes or additives affecting results. Unlike therapeutic phlebotomy, which involves larger volumes for direct treatment, diagnostic draws prioritize quality over quantity to support reliable downstream testing.[24][25]Therapeutic Phlebotomy
Therapeutic phlebotomy involves the controlled removal of blood to manage specific medical conditions characterized by excess red blood cell mass, iron overload, or other hematologic abnormalities, distinguishing it from historical indiscriminate bloodletting practices.[9] This procedure aims to alleviate symptoms, prevent complications, and normalize physiological parameters by reducing blood volume or specific components, such as iron bound to transferrin or ferritin.[7] It has evolved into a precise intervention within modern hematology, guided by laboratory monitoring and patient-specific protocols.[9] Primary indications for therapeutic phlebotomy include polycythemia vera, a myeloproliferative neoplasm causing overproduction of red blood cells; hereditary hemochromatosis, an iron overload disorder leading to organ damage; and porphyria cutanea tarda, a hepatic porphyria associated with elevated iron levels that exacerbate skin manifestations.[9] In polycythemia vera, phlebotomy reduces elevated hematocrit to mitigate risks of thrombosis and hyperviscosity.[7] For hemochromatosis, it depletes excess iron stores by removing iron-rich red blood cells, often serving as first-line therapy over chelation agents.[26] In porphyria cutanea tarda, the procedure lowers hepatic iron, which triggers porphyrin accumulation and photosensitivity.[9] Typically, 450-500 mL of blood is removed per session using standard venipuncture equipment, equivalent to one unit, though smaller volumes (e.g., 250 mL) may be used for patients with low body mass or comorbidities to avoid hemodynamic instability.[27] The frequency of therapeutic phlebotomy is tailored to the underlying condition and response, generally starting weekly until target levels are achieved—such as hematocrit below 45% in polycythemia vera or serum ferritin under 50 ng/mL in hemochromatosis—followed by maintenance sessions every 1-3 months to sustain remission.[26] No more than one to two units are removed in a 24-hour period to prevent acute volume depletion.[28] Monitoring involves pre-procedure assessments of hemoglobin, hematocrit, and ferritin, with post-procedure checks to ensure stability; replacement with intravenous normal saline (e.g., 500 mL) is administered if significant volume loss occurs or in patients prone to hypotension.[29] This targeted approach marks a significant historical shift from the broad, often harmful bloodletting of antiquity to evidence-based therapy refined in 20th-century hematology, where it became integral to managing chronic blood disorders following advances in understanding iron metabolism and erythropoiesis.[9]Procedure
Preparation and Patient Interaction
Prior to performing phlebotomy, thorough patient assessment is essential to ensure safety and the validity of diagnostic results. This includes verifying the patient's identity using at least two independent identifiers, such as full name and date of birth, to prevent errors in sample labeling and treatment.[30] Phlebotomists must also inquire about the patient's medical history, including any allergies to materials like latex gloves or antiseptics, previous experiences with difficult venipunctures, and relevant conditions such as anticoagulant therapy or low platelet counts that could increase bleeding risks.[31] Additionally, confirm adherence to specific preparation requirements, such as fasting for 8 to 12 hours prior to glucose or lipid panel tests, to avoid inaccurate results from dietary influences.[32] Effective communication and informed consent form the foundation of patient-centered phlebotomy. The phlebotomist should explain the procedure in clear, simple terms, including its purpose, expected sensations, and duration, while addressing any patient concerns or fears to reduce anxiety.[1] Verbal or written informed consent is obtained after this discussion, confirming the patient's understanding and agreement without coercion.[33] To minimize risks like vasovagal syncope, particularly in patients with a history of fainting or anxiety, position the patient in a seated chair with arm support or supine with legs elevated if needed; supine positioning reduces the risk of vasovagal syncope compared to sitting. Site selection begins with visual and palpatory examination of accessible veins, typically in the antecubital fossa of the arm. Select the non-dominant arm if possible, avoiding sites with intravenous lines, scars, or hematomas to prevent contamination or complications.[1] Apply a tourniquet 3 to 4 inches proximal to the intended venipuncture site to engorge the vein, but limit application to no more than 1 minute to avoid hemoconcentration, which can falsely elevate analyte levels such as potassium and proteins.[34] Hygiene protocols are critical to prevent infections during phlebotomy. Perform hand hygiene with soap and water or alcohol-based sanitizer before and after the procedure, then don clean, non-sterile gloves to protect both patient and phlebotomist.[35] Disinfect the selected venipuncture site using 70% isopropyl alcohol swabs in a circular motion from center outward, allowing 30 to 60 seconds to dry; for higher-risk cases like blood cultures, 2% chlorhexidine gluconate in 70% alcohol is preferred due to its superior antimicrobial efficacy over povidone-iodine.[36]Venipuncture Techniques
Venipuncture, the primary method for blood collection, involves inserting a needle into a vein to withdraw blood. The standard technique begins with the phlebotomist anchoring the vein using manual pressure or a vein finder, then inserting the bevel-up needle at a 15- to 30-degree angle relative to the skin surface. The needle is advanced slowly until a "flashback" of blood appears in the hub, confirming entry into the vein, at which point the collection tube or syringe is attached and blood is drawn by either evacuating the vacuum tube or pulling back on the syringe plunger. This method minimizes patient discomfort and vein trauma, with the angle ensuring efficient penetration while avoiding deeper structures. For patients with fragile, small, or difficult-to-access veins, such as the elderly or those with compromised vascular integrity, alternative methods are employed. The butterfly needle, or winged infusion set, features a short needle attached to flexible tubing and "wings" for stabilization, allowing shallower insertion angles (typically 10-15 degrees) and better control in areas like the hand or antecubital fossa. In low-flow situations, such as dehydrated patients or those with poor venous return, a syringe draw technique is preferred over vacuum tubes to prevent vein collapse; the phlebotomist uses a 5-10 mL syringe to gently aspirate blood in small increments. Adhering to the order of draw is essential to avoid cross-contamination between additives in collection tubes, as per Clinical and Laboratory Standards Institute (CLSI) guidelines.[37] The sequence prioritizes blood culture bottles first to prevent microbial contamination, followed by coagulation tubes (e.g., with sodium citrate), serum tubes (plain or with clot activator), and finally tubes with additives like heparin or EDTA to mitigate carryover effects. Deviations from this order can lead to erroneous test results, such as falsely elevated potassium levels from EDTA contamination. Throughout the procedure, time management is critical to ensure sample integrity and patient safety. The tourniquet should not remain applied for more than one minute to avoid hemoconcentration, which could alter analyte concentrations; it is released immediately after sufficient blood is collected. Collected tubes are then gently inverted 5-10 times, depending on the additive (e.g., 8-10 times for tubes with clot activators), to ensure proper mixing without causing hemolysis. This inversion promotes uniform distribution of anticoagulants or preservatives while preserving cellular components.Post-Draw Handling
After completing the venipuncture, the phlebotomist withdraws the needle gently and immediately applies direct pressure to the puncture site using a clean gauze pad or cotton ball to promote hemostasis and minimize bleeding. Pressure should be maintained firmly for 3 to 5 minutes, or longer if necessary, particularly for patients on anticoagulants, to prevent hematoma formation; the patient must keep the arm extended straight and elevated above heart level during this time, avoiding bending the elbow which could dislodge the forming clot.[38][39] Blood samples must be labeled immediately at the bedside or collection site to ensure traceability and compliance with accreditation standards, including the patient's full name, a second identifier such as date of birth or medical record number, collection date and time, and the phlebotomist's initials. These requirements, mandated by organizations like the College of American Pathologists (CAP) and the Joint Commission, use at least two patient-specific identifiers to reduce misidentification risks and support accurate diagnostic testing.[40][41][42] Following labeling, specimens are transported to the laboratory promptly under conditions dictated by the tube additive and test requirements to preserve sample integrity; for example, tubes with EDTA anticoagulant for complete blood count (CBC) analysis remain stable at room temperature for up to 24 hours, while serum tubes require centrifugation within 2 hours of collection to separate serum from cells. Refrigeration at 2–8°C is recommended for certain analytes sensitive to glycolysis, such as glucose, unless specified otherwise, and all transport adheres to guidelines from the Clinical and Laboratory Standards Institute (CLSI) to avoid hemolysis or contamination.[43][44] Patients receive clear post-procedure instructions to support recovery and monitor for minor complications like bruising, which may appear as discoloration at the site but typically resolves without intervention. They are advised to keep the bandage in place for at least 4–6 hours, avoid heavy lifting or strenuous arm use for 24 hours to prevent re-bleeding, and contact healthcare providers if excessive swelling, pain, or signs of infection develop.[39][45][46]Equipment and Supplies
Needles and Collection Devices
Phlebotomy needles are typically available in gauge sizes ranging from 20 to 25, with 21- to 23-gauge needles being the most common for adult venipuncture due to their balance of vein access ease and sufficient blood flow rates.[47][48] Thinner needles, such as 25-gauge or smaller, are preferred for pediatric patients or fragile veins to minimize trauma and hemolysis risk.[49] Multi-sample needles, often 21- to 22-gauge, feature a double-ended design with an integrated adapter compatible with evacuated tube systems like Vacutainer holders, allowing sequential blood draws without multiple punctures.[50] Blood collection can employ either syringe-based or vacuum extraction systems, each suited to specific clinical scenarios. Syringe systems, using a hypodermic needle attached to a manual syringe, provide precise control over draw pressure, making them ideal for patients with difficult or collapsed veins where over-aspiration might cause vein damage.[31] In contrast, vacuum systems utilize evacuated tubes that create negative pressure to automatically draw blood through the needle, enhancing efficiency in high-volume settings like routine laboratory draws by reducing procedural time and contamination risk during transfers.[50][47] Winged infusion sets, commonly known as butterfly needles, consist of a small-gauge needle (21- to 25-gauge) with stabilizing plastic wings and short flexible tubing, facilitating access to superficial or hard-to-reach veins such as those in the hands or in pediatric cases.[51] The winged design allows for better maneuverability and patient comfort during venipuncture, particularly when standard straight needles are impractical.[49] Recent innovations in phlebotomy equipment emphasize safety-engineered needles, which incorporate mechanisms like automatic shielding, retractable sheaths, or pivoting barriers to cover the bevel post-use, significantly reducing needlestick injury rates.[52] These devices align with OSHA's Bloodborne Pathogens Standard (29 CFR 1910.1030), which mandates the evaluation and adoption of safer sharps to protect healthcare workers from exposure to bloodborne pathogens.[53] The Centers for Disease Control and Prevention (CDC) estimates that 62 to 88 percent of sharps injuries can be prevented by using safer medical devices, significantly reducing percutaneous injuries in phlebotomy procedures when implemented alongside training.[54] As of 2025, emerging technologies include robotic venipuncture systems for automated blood draws and infrared vein finders to enhance visualization and accuracy.[55]Tube Types and Additives
Blood collection tubes are standardized with color-coded closures according to guidelines from the Clinical and Laboratory Standards Institute (CLSI), which specify recommendations for tube materials, additives, and labeling to ensure consistency in specimen collection across laboratories. These colors indicate the presence and type of additives, facilitating quick identification for specific laboratory tests and minimizing errors in sample processing. Common examples include red or gold-topped tubes for serum separation, lavender-topped tubes for hematology analyses, and light blue-topped tubes for coagulation studies.[56] Additives in these tubes serve critical functions in preserving blood components for accurate testing by either preventing clotting (anticoagulants) or promoting it (clot activators), while some inhibit metabolic processes to maintain analyte stability. For instance, ethylenediaminetetraacetic acid (EDTA) in lavender-topped tubes acts as an anticoagulant by chelating calcium ions, preserving whole blood morphology for complete blood count (CBC) tests.[56] Sodium citrate in light blue-topped tubes similarly anticoagulates by binding calcium, enabling plasma-based coagulation assays like prothrombin time (PT) and activated partial thromboplastin time (aPTT).[57] Lithium heparin in green-topped tubes prevents clotting via inhibition of thrombin, suitable for plasma chemistry panels where rapid processing is needed.[56] Gray-topped tubes contain sodium fluoride and potassium oxalate; the former inhibits glycolysis to stabilize glucose levels for up to 24 hours, while the latter anticoagulates, making them ideal for glucose tolerance testing.[57] Red-topped tubes typically lack additives or contain a clot activator like silica to promote rapid serum formation for immunoassays and electrolyte panels.[56] The following table summarizes key tube types, their color coding, additives, and primary uses based on CLSI standards:| Tube Color | Additive | Primary Use | Example Tests |
|---|---|---|---|
| Red/Gold | None or clot activator (e.g., silica) | Serum chemistry | Electrolytes, liver function[57] |
| Lavender | EDTA (K2 or K3) | Whole blood hematology | CBC, blood typing[56] |
| Light Blue | Sodium citrate (3.2%) | Plasma coagulation | PT, aPTT[57] |
| Green | Lithium heparin | Plasma chemistry | STAT electrolytes, ammonia[56] |
| Gray | Sodium fluoride/potassium oxalate | Plasma glucose preservation | Fasting glucose, lactate[57] |