Specimen collection and phlebotomy

In short

Specimen collection is the pre-analytical stage of laboratory testing — identifying the patient, choosing the right container and additive, drawing or receiving the sample, labelling it and delivering it in a stable condition to the bench. Phlebotomy is the skilled part of it: obtaining blood by venipuncture, capillary puncture or arterial puncture without harming the patient or the sample. It matters because roughly 60–70% of all laboratory errors arise before the analyser is ever switched on, and no instrument can correct a wrongly drawn or wrongly labelled sample. B.Sc MLT papers on clinical pathology and laboratory practice examine it heavily (order of draw, anticoagulants, blood-to-anticoagulant ratio, rejection criteria), and it is the first practical round in interviews at Dr Lal PathLabs, SRL, Metropolis, Thyrocare, Apollo, AIIMS and state medical college laboratories. NABL 112 / ISO 15189 require a documented primary sample collection manual, so every step below is also an auditable requirement.

Explained

Pre-analytical basics and patient preparation

• Pre-analytical phase — test request → patient identification → preparation → collection → labelling → transport → accessioning. Everything before analysis.
• Patient identification: minimum two independent identifiers (full name + unique ID / lab accession number / date of birth). Never identify by bed number or room alone. Ask the conscious patient to state their name rather than asking "Are you Mr X?"
• Informed consent: verbal consent is enough for routine venipuncture; written consent for HIV/HBV testing in many state protocols and for procedures on minors (guardian consents).
• Fasting: 8–12 h overnight fast (water allowed) for fasting glucose and lipid profile. Many Indian labs and current lipid guidelines now accept non-fasting lipids for screening — state the status on the form.
• Posture: 15 min seated/supine rest before draw; standing raises many analytes (aldosterone, renin, catecholamines, haematocrit) by haemoconcentration.
• Timing: cortisol (8 am), therapeutic drug monitoring (trough just before the next dose; digoxin ≥6–8 h post dose), blood cultures before antibiotics, GTT at exact intervals.
• Diurnal/physiological variation: cortisol, iron, serum potassium (rises with fist clenching), ACTH; exercise raises CK, AST, LDH.

Equipment, additives and the order of draw

• Systems: (1) evacuated tube system (Vacutainer / vacuette) — safest and preferred; (2) syringe and needle — for fragile or collapsed veins; (3) winged infusion set (butterfly), 23 G — paediatric and dorsal hand veins; (4) lancet for capillary puncture.
• Needle gauge: 21 G (green) adult routine, 22 G (black) small veins, 23 G butterfly paediatric; larger number = thinner needle. 16–18 G for blood donation (one unit, 350/450 mL).
• Additives: EDTA (dipotassium/tripotassium salt) chelates calcium; sodium citrate (3.2%, 1:9 ratio) chelates calcium reversibly; heparin (lithium, sodium, ammonium) activates antithrombin and inhibits thrombin; sodium fluoride is an antiglycolytic (not an anticoagulant) with potassium oxalate as the anticoagulant; clot activator (silica) and gel separator in serum tubes.
• Standard order of draw (CLSI H3 / NABL-adopted):
• Blood culture bottles (sterile first).
• Sodium citrate — blue (coagulation, PT/INR, APTT).
• Serum tube — red (plain) or gold/yellow (SST, gel + clot activator).
• Heparin — green (plasma chemistry, ABG, chromosome study, ammonia, lactate).
• EDTA — lavender/purple (CBC, ESR, HbA1c, blood group, HPLC for haemoglobinopathies).
• Fluoride/oxalate — grey (glucose, lactate).
• The order exists to prevent additive carry-over: EDTA carried into a chemistry tube falsely lowers calcium and magnesium and falsely raises potassium; heparin carried into an EDTA tube clumps platelets.
• Fill volume matters: citrate and EDTA tubes must be filled to the mark. Under-filled citrate → excess citrate → falsely prolonged PT/APTT. Under-filled EDTA → shrunken red cells, falsely low MCV and HCT.
• Mixing: 5–10 gentle end-over-end inversions immediately after filling; never shake (haemolysis) and never leave unmixed (clots/microclots).
• Special tubes: black (3.8% citrate 1:4, Westergren ESR), yellow ACD/SPS (HLA, culture), royal blue (trace metals), tubes with aprotinin/protease inhibitors for ACTH and gut hormones.

Venipuncture — step by step

1. Check the request form, test list, container requirement and patient preparation; verify identity with two identifiers.
2. Hand hygiene; wear gloves (mandatory under biomedical waste and lab-safety practice). Assemble labelled tubes, holder, needle, tourniquet, 70% isopropyl alcohol swab, gauze, tape, sharps container.
3. Position the arm extended and supported, palm up. Inspect both arms.
4. Site selection — antecubital fossa: median cubital vein first (large, well anchored, least painful), then cephalic (lateral, rolls more), then basilic (medial — last choice: median nerve and brachial artery lie close beneath). Then dorsal hand veins.
5. Apply tourniquet 7.5–10 cm (3–4 inches) above the site, snug enough to impede venous but not arterial flow; never more than one minute — longer causes haemoconcentration and raises potassium, total protein, calcium, lactate.
6. Palpate with the index finger (veins feel springy; arteries pulsate; tendons are hard and immobile).
7. Clean in concentric circles outward with 70% alcohol; allow to air dry (wet alcohol stings and haemolyses). For blood culture use chlorhexidine-alcohol or povidone-iodine with full 30–60 s contact instead; for blood alcohol/ethanol levels use a non-alcoholic antiseptic (povidone-iodine or aqueous benzalkonium chloride), never any alcohol-containing swab.
8. Anchor the vein below the site with the thumb; insert bevel up at 15–30° along the vein; advance a few millimetres after flashback.
9. Push tubes onto the holder in order of draw; let each fill by vacuum until flow stops. Release the tourniquet as soon as blood flows, and before the last tube is removed.
10. Remove the last tube from the holder first, then withdraw the needle in one smooth motion; apply gauze with pressure for 2–3 min (5–10 min if on warfarin/heparin); keep the arm straight — do not ask the patient to bend the elbow.
11. Activate the safety shield and discard the needle/holder as one unit in the puncture-proof white translucent sharps container — never recap, never detach by hand.
12. Invert tubes, verify labels at the bedside in the patient's presence, record time of collection and collector's identity, remove gloves, hand hygiene.
13. Labelling minimum: patient name, unique ID, date and time of collection, specimen type/site, collector's initials. Unlabelled or mismatched = rejection (except irreplaceable specimens, which follow a documented exception process).
14. Failed draw: reposition slightly, try a second tube (vacuum loss), or try the other arm. Maximum two attempts per phlebotomist, then escalate to a senior — this is an NABL-type documented rule in most Indian labs.

Capillary, arterial, paediatric and other specimens

• Capillary (skin) puncture: lateral or medial plantar heel in infants <6 months (never the central heel or the curve — calcaneus injury risk); side of the distal third of the 3rd/4th finger in older children and adults. Warm the site (≤42 °C), puncture depth ≤2.0 mm (heel), ≤1.5–2.4 mm per device, wipe away the first drop, let drops form freely — no milking/squeezing (tissue fluid dilution, haemolysis).
• Capillary order of draw is the reverse logic: blood gas → EDTA → other additives → serum, so the EDTA (CBC) sample is filled before platelets clump.
• Capillary blood is arteriolar-venous mixed: glucose slightly higher, potassium slightly lower and higher haemolysis-derived values than venous blood; results are not interchangeable with venous reference intervals.
• Arterial blood gas: radial artery first (collateral ulnar supply, confirmed by the modified Allen's test), then brachial, then femoral. Heparinised (dry lithium heparin) 2–3 mL syringe, 23–25 G, 45° to the skin, expel air bubbles, mix, cap; analyse within 15 min at room temperature or transport in ice slurry (plastic syringe on ice is discouraged for pO₂ — note local policy); firm pressure 5 min, 10 min if anticoagulated.
• Blood culture: skin antisepsis is the critical step; 2 sets from 2 different sites before antibiotics; adult 8–10 mL per bottle (blood-to-broth 1:5 to 1:10); paediatric 1–3 mL; disinfect bottle septum; never draw through an existing line unless catheter sepsis is suspected (then paired peripheral + line sample).
• Maximum blood volume in paediatrics: keep within about 1–5% of total blood volume in 24 h (neonatal blood volume ≈ 80–100 mL/kg) — a common viva question.
• Urine: midstream clean-catch for culture (sterile wide-mouth container, first morning preferred, ≤2 h at room temperature or 2–8 °C up to 24 h, or boric acid preservative); first morning for routine/microscopy and pregnancy tests; 24-h urine for creatinine clearance, VMA, protein, calcium — discard the first void, collect all urine including the same hour next morning, keep refrigerated with the correct preservative (HCl for VMA/catecholamines, acetic acid or thymol for others); catheter sample from the port, never the bag.
• Stool: clean dry container, no urine or water contamination; for ova/parasite 3 samples on alternate days; examine within 30–60 min for trophozoites or use PVA/formalin.
• Sputum: early morning deep cough, not saliva; for TB, India's NTEP accepts one spot sample for NAAT (CBNAAT/TrueNat) as the frontline test, with spot-and-morning microscopy where smear is used; sterile wide-mouth screw-capped container.
• Semen: 2–7 days abstinence, masturbation into a sterile wide-mouth container, deliver within 1 h at body temperature, complete sample (first fraction has most sperm).
• CSF: physician-collected by lumbar puncture into 3–4 sterile numbered tubes — tube 1 chemistry/biochemistry, tube 2 microbiology, tube 3 cell count/cytology (least contaminated by puncture blood), tube 4 extra/special tests; process immediately (cells lyse); never refrigerate a microbiology CSF (meningococci die).
• Swabs/body fluids: transport medium (Amies/Stuart) for swabs; sterile heparin or EDTA tube for synovial/pleural/ascitic fluid cell counts.

Specimen handling, transport, storage and rejection

• Separate serum/plasma from cells within 2 h of collection; glucose in a plain tube falls about 5–7% per hour by glycolysis (≈0.3–0.4 mmol/L/h) at room temperature — hence grey fluoride tubes.
• Light-sensitive: bilirubin, vitamin A, vitamin B6, porphyrins, carotene — amber tube or foil wrap.
• Chilled transport (ice slurry): ammonia, lactate, ACTH, PTH, gastrin, homocysteine, blood gases, renin.
• Keep at 37 °C: cryoglobulins, cold agglutinins, cryofibrinogen.
• Never refrigerate: blood for ESR/CBC beyond 24 h (store 2–8 °C up to 24 h for CBC; smears within 2–4 h for best morphology), CSF for culture, blood for potassium (cold causes leakage from cells → pseudohyperkalaemia).
• Transport: upright, leak-proof secondary container, triple packaging (primary vial, absorbent + secondary, rigid outer) with the biohazard symbol; Category B UN 3373 "Biological substance" for routine diagnostic shipping; cold chain with data logger for referred tests.
• Standard rejection criteria: unlabelled/mislabelled, mismatch between form and tube, wrong tube/additive, haemolysed (for K, LDH, AST, folate, haptoglobin), clotted EDTA/citrate sample, under- or over-filled coagulation tube, insufficient quantity (QNS), grossly lipaemic (reject only if assay-affected), sample drawn above an IV line, expired tube, excessive transport delay, leaked or broken container.
• Haemolysis causes: wet alcohol, too-thin needle, vigorous shaking, pulling a syringe plunger too fast, prolonged tourniquet, fist clenching, milking a finger, forcing blood through a needle into a tube, frozen-thawed whole blood, difficult draw. Effect: potassium, LDH, AST, phosphate, magnesium and iron falsely high; haptoglobin and some analytes falsely low; interferes with bilirubin and troponin.
• Drawing from a cannulated arm: always use the opposite arm; if unavoidable, stop the infusion 2 min, draw below the IV site and discard the first 5 mL. Never draw from the same side as a mastectomy, AV fistula, haematoma, burn, scar, oedema or paralysis.

Complications, safety and the Indian regulatory frame

• Local complications: haematoma (release tourniquet and withdraw at once, then pressure), pain, nerve injury (sharp shooting pain → withdraw immediately), inadvertent arterial puncture (bright red pulsatile blood → withdraw, 5–10 min pressure, inform physician), thrombophlebitis, infection, petechiae, allergy to latex/adhesive.
• Systemic: syncope — commonest; stop, lay the patient flat or head between knees, loosen clothing, cold compress, never leave alone, never use ammonia inhalants routinely; also nausea, vomiting, seizures.
• Iatrogenic anaemia from repeated draws in ICU/neonates — minimise volume and frequency.
• Needle-stick injury protocol: do not squeeze; wash with soap and running water (eyes/mucosa flush with water or saline); report immediately; risk assessment of source; PEP for HIV started ideally within 2 h and not beyond 72 h, three-drug regimen for 28 days under NACO guidance; hepatitis B — HBIG plus vaccine if unvaccinated/non-responder; baseline and follow-up testing at 6 weeks, 3 months and 6 months; record in the injury register.
• Transmission risk per percutaneous exposure (approximate): HBV up to ~30% in a susceptible host, HCV ~1.8%, HIV ~0.3%. Hepatitis B vaccination of all phlebotomists is standard.
• Standard precautions: treat every specimen as infectious; gloves for every draw, changed between patients; no recapping; sharps container replaced at three-quarters full.
• Waste segregation at the point of collection (Bio-Medical Waste Management Rules, 2016 as amended): needles/lancets/syringes with fixed needles → white translucent puncture-proof; blood-soaked cotton, gauze, gloves, blood bags → red (contaminated recyclable plastics: tubing, urine bags) and yellow (soiled waste, discarded blood/body fluids, laboratory waste requiring treatment); broken/discarded contaminated glass, including medicine vials and ampoules, and metallic body implants → blue. (Detailed treatment and disposal belong to the waste topic.)
• Quality and accreditation: NABL 112 (medical testing laboratories, to ISO 15189) requires a documented primary sample collection manual, trained and authorised collectors, unique identification, defined acceptance/rejection criteria, and monitored pre-analytical quality indicators (rejection rate, haemolysis rate, mislabelling rate, TAT).
• Other Indian provisions: Clinical Establishments (Registration and Regulation) Act, 2010 in adopting states; the Drugs and Cosmetics Act with blood-centre licensing for donor phlebotomy; HIV and AIDS (Prevention and Control) Act, 2017 — informed consent and confidentiality for HIV testing; MTP and PCPNDT rules where antenatal samples are involved. Occupational safety for lab workers now sits under the Occupational Safety, Health and Working Conditions Code, 2020, one of the four Labour Codes in force from 21 November 2025, which replaced the Factories Act, 1948 and related Acts.

Key points

• Pre-analytical phase — everything before analysis; source of about 60–70% of total laboratory errors.
• Two identifiers — name plus a unique ID, verified from the patient wherever possible; bed number is never an identifier.
• Order of draw — culture, citrate (blue), serum (red/gold), heparin (green), EDTA (lavender), fluoride (grey); prevents additive carry-over.
• EDTA — calcium chelator, the anticoagulant for CBC, ESR, HbA1c and blood grouping; about 1.5 mg per mL of blood.
• Citrate 1:9 — 3.2% sodium citrate for PT/INR and APTT; 3.8% citrate at 1:4 for the Westergren ESR.
• Heparin — antithrombin activator; plasma chemistry, ABG, ammonia, lactate, karyotyping; not for blood smears (blue-grey background).
• Fluoride-oxalate — fluoride is an antiglycolytic preservative for glucose, oxalate the anticoagulant.
• Tourniquet ≤1 minute — longer gives haemoconcentration: high potassium, protein, calcium, lactate.
• Median cubital vein first, basilic last (median nerve and brachial artery lie beneath it).
• Needle angle 15–30°, bevel up; release the tourniquet as soon as blood flows.
• Mix by 5–10 gentle inversions; shaking haemolyses, no mixing clots.
• Haemolysis falsely raises K, LDH, AST, phosphate and iron — the commonest rejection reason after labelling errors.
• Capillary puncture — lateral/medial plantar heel in infants, depth ≤2 mm, discard the first drop, never milk.
• Modified Allen's test before radial arterial puncture; ABG analysed within 15 minutes.
• CSF tubes numbered 1–4: chemistry, microbiology, cell count, extra; process immediately, never refrigerate for culture.
• Separate serum from cells within 2 h; glucose falls 5–7% per hour in a plain tube.
• Needle-stick — wash, report, PEP within 2 h and never beyond 72 h (NACO); hepatitis B vaccination of all phlebotomists.
• NABL 112 / ISO 15189 — mandates a primary sample collection manual and monitored rejection, haemolysis and mislabelling rates.

Formulas and examples

Example 1 — citrate adjustment for polycythaemia. A patient has HCT 68%; a 2.7 mL draw tube contains 0.3 mL of 3.2% citrate (total 3.0 mL).

• Required citrate C = 1.85 × 10⁻³ × (100 − 68) × 2.7 = 1.85 × 10⁻³ × 32 × 2.7 = 0.1598 ≈ 0.16 mL.
• So 0.14 mL of citrate must be removed from the tube before drawing 2.7 mL of blood (or a specially prepared tube used); otherwise the excess citrate binds extra calcium and the PT/APTT come out falsely prolonged.

Example 2 — EDTA requirement and an under-filled tube. A 4 mL K₂EDTA tube is designed for 4 mL of blood.

• Correct EDTA = 1.5 mg/mL × 4 = 6 mg in the tube.
• A technician fills only 2 mL. Effective concentration = 6 mg / 2 mL = 3.0 mg/mL — double the specification.
• Consequence: red cells shrink osmotically → MCV and HCT falsely low, MCHC falsely high; platelets may clump. Such a sample is rejected and re-drawn, not "corrected".

Example 3 — maximum safe paediatric draw. A 3 kg neonate; TBV at 85 mL/kg.

• TBV = 3 × 85 = 255 mL.
• Safe limit at 1% in 24 h = 2.55 mL; at the upper 5% limit = 12.75 mL.
• A requested panel needing 6 mL is within the 5% ceiling but well above the conservative 1% guidance — collect by capillary/micro-tubes, prioritise tests, and consult the paediatrician. Repeated 6 mL draws over days cause iatrogenic anaemia.

Example 4 — creatinine clearance from a 24-h urine. Volume 1,500 mL, urine creatinine 90 mg/dL, plasma creatinine 1.2 mg/dL.

• Urine creatinine excreted = 90 mg/dL × (1,500/100) dL = 1,350 mg in 24 h.
• CrCl = (90 × 1,500) / (1.2 × 1,440) = 135,000 / 1,728 = 78.1 mL/min.
• Interpretation note: an incomplete collection (a missed void) lowers V and gives a falsely low clearance — which is why collection instructions are part of the pre-analytical procedure.

Example 5 — glucose loss in the wrong tube. Blood is drawn in a plain red tube at 9:00 am with a true glucose of 110 mg/dL and separated only at 12:00 noon at room temperature, with glycolysis at 6% per hour.

• Loss over 3 h ≈ 110 × (1 − 0.94³) = 110 × (1 − 0.8306) = 110 × 0.1694 ≈ 18.6 mg/dL.
• Reported value ≈ 91 mg/dL — a diabetic screening result turned normal by a pre-analytical error. A grey fluoride tube or separation within 2 h prevents it.

Where it is used

• Diagnostic chains and collection centres: Dr Lal PathLabs, SRL Diagnostics, Metropolis, Thyrocare, Agilus, Apollo Diagnostics — phlebotomist and home-collection roles; pre-analytical rejection rate is a monitored KPI and often a pay-linked metric.
• Hospital central laboratories and ICUs: AIIMS, PGIMER, CMC Vellore, state medical colleges — ward rounds for morning draws, ABG sampling with critical-care teams, CSF and body-fluid handling.
• Blood centres and voluntary camps: donor selection, 16–18 G donor phlebotomy into 350/450 mL CPDA/SAGM bags with a mixer, pilot tubes for grouping and TTI screening under Drugs and Cosmetics licensing and NBTC guidelines.
• Public-health programmes: NTEP sputum collection for CBNAAT/TrueNat, NACO ICTC/HIV sample collection with pre- and post-test counselling, NVHCP hepatitis screening, dried blood spot collection in newborn screening programmes.
• Clinical trials and CRO work: Syngene, Lambda, Veeda — strict time-point sampling, chain-of-custody and GCP documentation for pharmacokinetic draws.
• Job roles: phlebotomist, home-collection technician, laboratory technician/technologist, pre-analytical or accessioning supervisor, quality coordinator preparing for an NABL 112 assessment.

Interview questions

• Q: Why is the median cubital vein the first choice? A: It is large, superficial, well anchored by fascia so it does not roll, relatively painless, and it is not lying directly over the brachial artery or the median nerve.
• Q: Why must a blood culture be collected before any other tube? A: To keep it sterile — drawing it first avoids skin flora and additive carry-over from non-sterile tubes, which would give a false-positive culture.
• Q: What happens if a coagulation tube is only half filled? A: The blood-to-citrate ratio falls below 9:1, so excess citrate binds the calcium added in the assay and the PT and APTT are falsely prolonged; the sample must be rejected.
• Q: Why should a tourniquet not stay on for more than a minute? A: Venous stasis causes haemoconcentration and local anaerobic metabolism, falsely raising potassium, total protein, calcium, lactate and haematocrit.
• Q: Name five effects of haemolysis on results. A: Falsely high potassium, LDH, AST, phosphate and iron (also magnesium), with falsely low haptoglobin and interference in bilirubin and troponin assays.
• Q: A doctor asks for CBC, PT and glucose from one draw — which tubes and in what order? A: Light blue citrate first, then lavender EDTA, then grey fluoride — citrate before EDTA so no EDTA carries over into the coagulation tube.
• Q: Why must the central area of an infant's heel never be punctured? A: The calcaneus lies close to the skin there and can be injured, causing osteochondritis or osteomyelitis; the lateral or medial plantar surface is safe.
• Q: What is the modified Allen's test and when is it done? A: Occluding both radial and ulnar arteries, then releasing the ulnar and watching the palm flush within about 5–15 seconds; it confirms collateral circulation before a radial arterial puncture.
• Q: The only accessible vein is in an arm with a running IV drip — what do you do? A: Prefer the other arm; if there is no choice, stop the infusion for about two minutes, draw distal to (below) the IV site, discard the first 5 mL and record the circumstance.
• Q: Why is glucose collected in a grey-top tube? A: Sodium fluoride inhibits glycolysis by red cells and leucocytes, which otherwise consumes about 5–7% of the glucose per hour at room temperature.
• Q: You have failed twice on the same patient. What next? A: Stop and hand over to a senior or another trained phlebotomist — most laboratory SOPs, in line with NABL 112 expectations, limit one collector to two attempts.
• Q: What are the first steps after a needle-stick injury? A: Do not squeeze the wound; wash with soap and running water, report immediately, get a risk assessment and baseline testing, and start HIV PEP within two hours where indicated — never beyond 72 hours.

Common mistakes

• Writing the order of draw with EDTA before the citrate or serum tube, or omitting the blood culture from the sequence altogether.
• Confusing additive functions — calling fluoride an anticoagulant on its own, or heparin a calcium chelator.
• Leaving the tourniquet on until the last tube is filled, or letting the patient pump the fist (potassium rises).
• Puncturing before the alcohol dries, then reporting a haemolysed sample as a "patient problem".
• Labelling tubes away from the bedside or after leaving the patient — the root cause of most misidentification events.
• Topping up an under-filled EDTA or citrate tube from a second draw, or decanting blood between tubes, instead of re-collecting.
• Recapping needles or detaching them by hand, and dropping sharps into the red/yellow bag instead of the puncture-proof sharps container.

Related topics

• Laboratory quality control and NABL · Laboratory safety · Biomedical waste management · Laboratory instruments · Haematology: CBC and blood smear · Clinical biochemistry: serum and plasma analytes.