Phlebotomy: Order of Draw, Tube Types, and Common Lab Panels

Capillaries and gas diffusion

• Capillaries: thin-walled vessels where gases diffuse between blood and tissues.
• Diffusion rate: Capillaries diffuse gases quickly, not slowly; the idea that diffusion is slow is false. An analogy used: diffusion is faster through thinner material (like a thin cloth) than through a thick one, which is why diffusion can be rapid in capillaries.

Order of Draw (clinical sampling sequence)

• Blood culture tubes must be collected first because they are sterile and to avoid contamination of other tubes.
• Common order discussed: Yellow (blood cultures) → Light Blue → SST (Gold/Tiger Top) → Green (Heparin) → Lavender (EDTA) → Gray (Potassium Oxalate/Fluoride).
• Rationale: The order minimizes cross-contamination of additives between tubes which can affect test results.
• If using a butterfly needle with a light blue tube, labs may require discarding the first tube to remove air from the tubing so subsequent samples are filled properly.
• Filling rules: Light blue tube must be filled to the correct volume; some instances require fully filling the tube to maintain proper blood-to-anticoagulant ratio.
• Lab priority: Some tests are very sensitive to contamination or partial fills; labs may flag “quantity insufficient” if tubes aren’t filled correctly.
• Air and tubing considerations: When air remains in the line or if air pockets are not cleared, the sample can be rejected or yield erroneous results.
• In real-world practice, some tests (e.g., lab-critical tests) may require specific handling or order preferences beyond the basic mnemonic.

Tube additives and handling

• Yellow top: Blood cultures (sterile) — aerobic and anaerobic bottles; designed to keep cultures from clotting and to preserve pathogens.
• Light Blue top: Sodium citrate anticoagulant; used for coagulation testing; must be filled to the correct volume.
• SST / Gold / Tiger Top: Serum Separator Tubes; contain clot activator and serum separator gel; used for a wide range of chemistry and serology tests.
• Green / Light Green top: Heparin (usually plasma is collected); used for chemistry panels and other tests where plasma is preferred.
• Lavender top: EDTA anticoagulant; used for CBC and certain hematology tests; forms a white blood cell/differential and platelet counts.
• Gray top: Potassium oxalate with fluoride; used for glucose testing and some others; important to avoid contamination because potassium in gray tubes can skew potassium-related tests in other tubes if drawn out of order.
• Glass red top tubes: Older style; if glass, wrap in foam to prevent breakage; if plastic, less concern about breakage.
• Red/Gold/SST vs glass considerations: SSTs are red/gold-like tubes; their coating and separation gel can impact certain assays if not compatible with the test.
• Contamination caution: Mixing two additives is like oil and water; it can contaminate specimens and distort results.
• In practice, some tests must be run on dedicated tubes (example below), even if other tests could be combined on the same draw.

Special handling notes for certain tests

• Some tests must be drawn alone (must be by themselves):
  • Digoxin level (often SST) – needs full, undiluted blood for accurate measurement.
  • Vancomycin troughs (Vanco trough) – used to monitor antibiotic dosing; requires precise timing and isolation from other tests.
• Other tests can be drawn from the same tube when compatible, but the system may require separate tubes if the test is highly sensitive to contamination or if the assay requires a specific matrix (serum vs plasma).
• Example of compatibility: Digoxin and Vanco troughs generally require isolated handling; other common panels can share a tube if test requirements align (e.g., some SSTs carrying multiple serology/chemistry tests).
• Lab guidance: The order and combination of tests are often dictated by the automated lab system’s prompts; the system can indicate how many SSTs/Lavender tubes are needed for a given order.

Common tests by tube color and typical panels

• SST (Gold/Tiger Top):
  • BNP (B-type Natriuretic Peptide)
  • CMP (Comprehensive Metabolic Panel) / “Chemistry Panel”
  • Electrolytes
  • Hepatic function panels; hepatitis panels
  • TSH (Thyroid-Stimulating Hormone), T4 and free T4
  • BUN (Blood Urea Nitrogen) and Creatinine (kidney function)
  • Amylase and Lipase (pancreatic enzymes)
  • Iron and Ferritin (anemia workups)
  • PSA (Prostate-Specific Antigen)
  • ANA (Antinuclear Antibody) discussed later; may be run on SST depending on protocol
  • RPR (Rapid Plasma Reagin for syphilis)
  • Folate (often paired with iron)
  • C-reactive protein, calcium, and other chemistry markers
• Lavender (EDTA):
  • CBC (Complete Blood Count)
  • HbA1c (Hemoglobin A1c) – measures average blood glucose over ~3 months
  • Other hematology panels depending on needs
• Light Blue (Sodium Citrate):
  • Coagulation studies; e.g., PT/INR, aPTT
• Gray (Potassium Oxalate/Fluoride):
  • Glucose testing and certain glucose-related panels; can affect potassium measurements if contamination occurs
• Red (Glass) / Red-Top (Plastic, serum):
  • Previously used for many serology and chemistry tests; many labs now use SST for these tests
• Urine tests:
  • Routine urinalysis (dipstick and microscopic)
  • Microalbumin (kidney function, especially in diabetics)
  • Urine culture sometimes ordered separately; not part of routine blood draw per se

Common clinical panels and frequency

• Routine panel frequently ordered every 3 months for many patients:
  • CBC (Lavender)
  • CMP (SST/Gold) or BMP (Basic Metabolic Panel; often 7 tests) – chemistry panel
  • HbA1c (often included in routine diabetes monitoring)
  • Lipids (often part of CMP; cholesterol and triglycerides)
  • TSH (chemistry panel)
• HbA1c: measures average blood glucose over approximately the last 3 months; used to screen for and monitor diabetes; lower HbA1c indicates better glucose control.
• Urinalysis and microalbumin: commonly included to monitor kidney function, particularly in diabetics or hypertensive patients; microalbumin measures kidney function earlier in diabetic nephropathy.
• CMP vs BMP:
  • BMP (Basic Metabolic Panel): typically 7 tests; basic organ function and electrolyte status.
  • CMP (Comprehensive Metabolic Panel): typically 14 tests; broader panel including liver enzymes and protein levels in addition to the BMP set.

Practical testing examples and cross-test considerations

• HbA1c vs glucose at visit time:
  • HbA1c reflects the average glucose over ~3 months, not just the most recent readings; a patient may feel well for a few weeks, but HbA1c will reveal past elevated glucose levels.
• Glucose and potassium handling in gray tubes:
  • If a gray top is drawn first, potassium oxalate residue can contaminate subsequent samples (e.g., CMP or BMP), falsely elevating potassium readings; this is a major concern because elevated potassium can be life-threatening.
  • To prevent this, labs may require drawing gray top last or using dedicated tubes for tests sensitive to potassium levels.

Urine collection and ordering logic

• In real-world practice: urine collection is often intended to occur before blood draws, but in some classroom or clinic scenarios, urine may be collected last.
• Reasons for collecting urine first in real-world settings:
  • Reduces risk of contaminating the patient’s blood draw with urine or vice versa.
• Reasons to collect urine last in a training setting:
  • To avoid delaying other tests or patient workflow; but it can increase risk of hand contamination if patients do not wash hands.
• Contamination risks discussed:
  • If a patient does not wash hands, cross-contamination can occur between samples or with surfaces (e.g., chairs, counter tops); this is why some sites collect urine separately or use separate areas/equipment to minimize contamination.
• Occupational safety considerations:
  • Hand hygiene, chair disinfection, and minimizing cross-contact with samples are emphasized to reduce infection risk for healthcare workers.

Safety, OSHA, and proper disposal

• Needle disposal: needles are biohazard and must be disposed of in sharps containers.
• Safety devices: needles must be disposed of with the safety device engaged; adapters must remain on during disposal.
• OSHA and fines: improper disposal practices (e.g., leaving adapters off, gauze, alcohol swabs, or uncapped needles in sharps containers) can result in fines.
• Example penalties: $10,000 fine per incident if sharps container is not properly engaged or if non-sharps materials are disposed of improperly in sharps containers; multiply by number of items and incidents for a total fine estimate.
• Best practices:
  • Use the correct sharps container and ensure safety mechanisms are activated during disposal.
  • Do not place non-sharps (gauze, alcohol swabs) in sharps containers.
  • Periodically check containers for compliance during OSHA inspections.

Mnemonics to remember the order of draw

• First mnemonic (as presented):
  • "Young little boys giggle giggle like girls" → Yellow, Light Blue, SST, Green, Lavender, Gray.
• Second mnemonic (alternative):
  • "Young little boys really gossip like girls" → Yellow, Light Blue, SST, Green, Lavender, Gray.
• Notes:
  • Both mnemonics help recall the basic sequence of tube colors and their general category (blood cultures, coagulation, serum chemistry/serology, plasma/chemistry, hematology, chemistry with oxalate).
  • The lavender (EDTA) sits after green and before gray in the order, and blue (sodium citrate) sits early to preserve clotting information.

Practice scenario and workflow tips

• Example doctor’s order: PT/INR, CBC, ANA, CMP, and other tests.
  • Determine tube colors needed: Light blue (PT/INR), SST (CMP), Lavender (CBC, possibly HbA1c depending on protocol), and additional tubes as needed.
  • Decide order of draw: Blue first, then Lavender, etc., consistent with the mnemonics and lab requirements.
  • Some tests can be drawn from the same tube (e.g., CBC and HbA1c sometimes share a lavender tube depending on lab protocol), but others must be isolated (e.g., Digoxin, Vanco trough) due to assay requirements.
• Real-world lab prompts: Modern automation often indicates how many SSTs/Lavender tubes are needed for a given order and which tests must be run on separate tubes.
• Education-focused practice: A class activity included a Kahoot exercise to reinforce the order and tube selection through interactive questions.

Real-world implications and ethical considerations in phlebotomy practice

• Accuracy is critical: improper order of draw or contaminated samples can lead to misdiagnosis, unnecessary treatment, or missed diagnoses (e.g., false high potassium).
• Patient safety: correct needle disposal and adherence to safety protocols protect healthcare workers from sharps injuries and reduce infection risk.
• Regulatory compliance: OSHA fines and institutional penalties enforce strict compliance with disposal and handling protocols.
• Patient communication: explaining the order of draw and the need to fill tubes correctly helps patients understand why the procedure takes time and why accuracy matters for their care.

Quick recap of key takeaways

• Capillaries diffuse gases quickly; diffusion is not slow in capillaries.
• The order of draw matters to prevent contamination and erroneous results; follow the mnemonics and lab-specific guidelines.
• Yellow (blood cultures) must be first; Light Blue is for coagulation; SST/Gold/Tiger Top for many chemistry/serology tests; Green, Lavender, Gray follow in that order.
• Some tests must be drawn alone (Digoxin, Vancomycin troughs); others can share tubes depending on compatibility.
• Ensure tubes are filled to the correct volume, especially Light Blue; discard the first draw if using butterfly needles when required by protocol.
• Glass red top tubes require foam wrapping if broken; plastics are safer for handling.
• Urine collection order and hand hygiene are important to prevent cross-contamination.
• Safety devices and proper disposal are essential to avoid OSHA fines and protect staff.
• Common panels to know: CBC (Lavender), CMP and BMP (SST), HbA1c, Lipids, TSH, Renal/Metabolic tests, PSA, ANA, RPR, Folate, CRP, Calcium, Iron/Ferritin, Amylase/Lipase, and Urinalysis with microalbumin.
• Understanding how tests map to tubes helps in planned order and efficient blood collection during patient visits.

Practice prompt to apply knowledge

• If a doctor orders PT/INR, CBC, and ANA for a patient, which tubes and in what order would you draw according to the mnemonics and discussion? Consider: light blue for PT/INR, lavender for CBC (and possibly ANA depending on protocol), and SST for ANA if compatible; determine whether ANA can be drawn in the same SST as CMP depending on the lab’s rules and whether any test must be isolated.
• Discuss why Digoxin level and Vancomycin troughs must be drawn separately and how this affects the draw plan.