Tube stopper color, additive, specimen type, and typical CLSI draw-order position for widely used evacuated blood collection tubes. Based on CLSI GP41 and manufacturer reference knowledge.
Details vary by manufacturer and facility — always verify against your institution’s SOP. Pending NP clinical review.
| Stopper color | Also known as | Additive | Specimen | CLSI draw order | Common uses |
|---|---|---|---|---|---|
| Gold | SST, serum separator tube | Clot activator + gel separator | Serum | 3rd (after citrate) | Chemistry panels (CMP, BMP), +4 more |
| Red | Plain red, tiger top (older style) | None (or clot activator without gel) | Serum | 3rd (same position as gold) | Select chemistry and serology tests, +2 more |
| Lavender / Purple | EDTA tube | K2 EDTA (anticoagulant) | Whole blood or EDTA plasma | 5th | CBC with differential, +3 more |
| Light blue | Citrate tube, sodium citrate tube | 3.2% sodium citrate (anticoagulant) | Citrated plasma | 2nd (first after blood cultures) | PT / INR, +4 more |
| Green | Heparin tube | Lithium heparin or sodium heparin | Plasma (heparinized) | 4th | STAT chemistry panels, +3 more |
| Gray | Fluoride/oxalate tube | Sodium fluoride + potassium oxalate | Plasma (glycolysis-inhibited) | 6th (last) | Fasting glucose, +2 more |
| Royal blue | Trace element tube | Varies — none (serum), K2 EDTA, or sodium heparin: check the label | Serum or plasma (trace element-grade) | As required by test | Heavy metals (lead, mercury), +2 more |
| Pink | Blood bank EDTA tube | K2 EDTA | Whole blood (EDTA) | 5th (same position as lavender) | Blood bank type & screen, +2 more |
The gel migrates during centrifugation to form a physical barrier between serum and clot. Allow adequate clot time before centrifuging — commonly 30 minutes for SST/gel tubes; plain red tubes without additive may require longer. Follow manufacturer labeling.
Plain red tubes have no additive and no gel. Some versions contain a clot activator without gel. Note: many type & screen and crossmatch workflows at blood banks use pink EDTA tubes rather than red or tiger-top tubes — verify the required tube with your blood bank before drawing.
EDTA chelates calcium to prevent clotting. Mix with 8–10 gentle inversions immediately after collection. EDTA can interfere with calcium and magnesium assays if there is carryover.
Fill volume is critical — the 9:1 blood-to-citrate ratio must be exact or results are invalid. With a butterfly needle, draw a discard tube first to purge air from the tubing.
Mix with 8–10 gentle inversions immediately after collection. Do not use for coagulation tests — heparin falsely prolongs PT/PTT. Lithium heparin is the most common form; use sodium heparin only when lithium would interfere with the assay.
Sodium fluoride blocks glycolysis so cells cannot consume glucose during transport. Not appropriate for most other chemistry tests — fluoride inhibits many enzyme-based assays.
Stopper and interior surfaces are manufactured to very low trace-element specifications. Additive version varies — always confirm against the test requisition before drawing. Draw order depends on the additive: plain (serum) royal blue tubes follow the same position as other serum tubes; EDTA royal blue tubes follow the same position as other EDTA tubes; heparin royal blue tubes follow the same position as other heparin tubes.
Functionally identical to lavender EDTA, but color-coded specifically for blood bank specimens at many facilities to reduce transfusion-related labeling errors. Usage varies by institution.
An SST (serum separator tube) is used to collect serum for most routine chemistry tests. It contains a clot activator to speed clotting and a gel separator that migrates during centrifugation to form a physical barrier between serum and clot. Common tests include comprehensive and basic metabolic panels, lipid panel, thyroid function (TSH, T4), hepatic function, and most immunology assays. SST tubes typically have a gold stopper; allow 30 minutes of clot time before centrifuging.
"Tiger top" or "marble top" is used inconsistently across facilities and manufacturers. At some institutions it refers to the older red-and-black striped tube without gel; at others it is used interchangeably with SST or gold top. Always confirm which tube is actually stocked at your facility and whether it contains a gel separator before substituting one for the other.
EDTA (ethylenediaminetetraacetic acid) prevents clotting by chelating calcium ions, a required cofactor in the coagulation cascade. Without calcium, blood cannot clot, so cells remain intact and suspended in plasma — making EDTA tubes ideal for CBC, differential, and blood smear evaluation where intact cell morphology matters. Mix immediately after collection with 8–10 gentle end-over-end inversions.
A gold top tube is a serum separator tube (SST) containing a clot activator and a gel separator. It is the standard tube for most chemistry, endocrinology, and immunology panels — CMP, BMP, lipid panel, thyroid, hepatic function, and many specialized tests. At labs that have standardized on the gold stopper, "gold top" and "SST" are used interchangeably.
The light blue citrate tube is drawn before the green heparin tube to prevent heparin carryover. Even trace amounts of heparin can inhibit clot formation and falsely prolong clot-based coagulation results such as PT/aPTT. When using a butterfly needle, draw a plain discard tube before the light blue tube to purge dead air from the tubing so the citrate tube fills to the correct volume and maintains the critical 9:1 blood-to-citrate ratio.
Serum is the liquid remaining after blood has clotted and the clot has been centrifuged out; it contains no fibrinogen or clotting factors. Plasma is the liquid remaining after anticoagulated blood is centrifuged; it retains fibrinogen and other coagulation proteins. Serum tubes (red, gold/SST) have no anticoagulant or use a clot activator. Plasma tubes (lavender, green, light blue, gray) contain an anticoagulant. Many assays specify one or the other — substituting the wrong tube type can alter results.
A gray top tube is used primarily for glucose and lactate testing. It contains sodium fluoride (which blocks glycolysis so red cells cannot consume glucose during transport) and potassium oxalate (an anticoagulant). It is not appropriate for most other chemistry tests because fluoride inhibits many enzyme-based assays.
Royal blue top tubes are used for trace element, heavy metal, and toxicology testing (zinc, copper, selenium, lead, mercury, and similar analytes) where contamination from standard tube additives would corrupt the result. The stopper and tube surfaces are manufactured to very low trace-element specifications. Royal blue tubes come in different additive versions — no additive (serum), K2 EDTA, or sodium heparin — so always check the tube label and the test requisition before drawing.
Additive carryover occurs when trace amounts of the additive from one tube transfer to the needle hub and enter the next tube drawn, potentially altering its results. For example, EDTA from a lavender tube can chelate calcium and falsely lower ionized calcium in a subsequent serum tube. The CLSI-recommended order of draw (blood cultures → citrate → serum → heparin → EDTA → fluoride) sequences tubes to minimize the analytical harm of any carryover that does occur.
Inverting tubes immediately after filling mixes blood with the additive. Anticoagulant tubes (EDTA, heparin, citrate, fluoride) must mix promptly to prevent micro-clots; clot activator tubes (SST, gold top) must mix so the activator contacts all the blood evenly. Most tubes require 5–10 gentle end-over-end inversions (EDTA and heparin tubes typically 8–10); follow manufacturer labeling for the specific tube in use. Do not shake vigorously — that causes hemolysis and interferes with many assays.
CLSI guidelines recommend this sequence for evacuated tube collection: (1) blood culture bottles, (2) sodium citrate / light blue, (3) serum tubes — plain red or gold/SST, (4) heparin / green, (5) EDTA — lavender or pink, (6) fluoride/oxalate / gray. Individual institutions may have facility-specific modifications — always follow your own SOP. With a butterfly needle, draw a discard tube before the light blue tube to account for dead air volume in the tubing.
Source & scope: This guide reflects CLSI GP41 phlebotomy guidelines and widely published manufacturer reference materials (BD Vacutainer, Greiner Bio-One). Yellow/ACD and black/ESR tubes are not covered here. Tube specifications, additive formulations, and draw order may vary by facility — always verify against your institution’s standard operating procedure and the ordering lab’s specimen collection manual. Pending NP clinical review; not yet approved for publication. Last updated July 2026.