Written and maintained by CASRAI Editorial Board
Last updated
This page describes products and general use; it is not medical advice.
Who uses it: clinic and laboratory staff, buyers and students who need to know what is inside a gray top (grey cap or stopper) blood collection tube. After reading you should be able to name the two additives, say what the regulator-listed tube descriptor means, and see how listed products differ.
What the gray top tube additive is
A gray top tube contains sodium fluoride and potassium oxalate. Registered product records in the FDA-supplied AccessGUDID data (openFDA, checked 2026-10-30) describe these tubes by name as “Sodium Fluoride / Potassium Oxalate”. Potassium oxalate acts as the anticoagulant and sodium fluoride as the antiglycolytic agent.
The GMDN term attached to most of these records is “Evacuated blood collection tube IVD, anticoagulant/antiglycolytic”. Its definition describes a sealed tube holding a pre-measured vacuum, an anticoagulant (examples include potassium oxalate) and an antiglycolytic agent (examples include sodium fluoride), intended for collecting, preserving and transporting blood for analysis, with blood glucose or lactate determinations given as examples. It is a single-use device.
How it is built and regulated
The tube is a glass or plastic tube sealed with a stopper, with the additive pair already inside. In the United States, blood collection tubes fall under 21 CFR 862.1675, which defines a blood specimen collection device and lists blood collection tubes, vials, systems, serum separators and vacuum sample tubes among generic types. It is a Class II device. In the FDA product classification database, the code JKA is named “Tubes, Vials, Systems, Serum Separators, Blood Collection” and the code GIM is named “Tubes, Vacuum Sample, With Anticoagulant”; both list regulation 862.1675, Class 2.
Types and variants
The table compares gray-tube records listed in the FDA data (checked 2026-10-30). Every row comes from the product’s own registered description.
| Manufacturer and product | Additive amounts as listed | Size as listed | FDA product code | GMDN term in record |
|---|---|---|---|---|
| BD, Vacutainer Sodium Fluoride/Potassium Oxalate | “5mg/4mg” in the product name | Not stated in the record | JKA | Anticoagulant/antiglycolytic |
| Greiner Bio-One, VACUETTE FX Sodium Fluoride / Potassium Oxalate, grey cap-white ring | Not stated in the record | 2 ml, 13×75 | JKA | Anticoagulant/antiglycolytic |
| Greiner Bio-One, VACUETTE FX Sodium Fluoride / Potassium Oxalate, grey cap-black ring | Not stated in the record | 4 ml 13×75; 5.5 ml and 6 ml 13×100 | JKA | Anticoagulant/antiglycolytic |
| Cardinal Health, Monoject silicone coated gray stopper | 12.5 mg sodium fluoride and 10 mg potassium oxalate (5 mL draw) | 5 mL: 13 mm diameter, 75 mm length | GIM | Non-evacuated blood collection tube IVD, no additive |
| Cardinal Health, Monoject silicone coated gray stopper | 25 mg sodium fluoride and 20 mg potassium oxalate (10 mL draw) | 10 mL: 16 mm diameter, 100 mm length | GIM | Non-evacuated blood collection tube IVD, no additive |
Two points follow from the table. Additive amounts differ between manufacturers and between draw volumes, so the figure on one product does not transfer to another. And the registry descriptor is not uniform: the Monoject records carry a GMDN term reading “no additive” even though their descriptions name both additives, so the product’s own labelling is the reference for what is inside.
Yellow top tubes
People who search for gray top tubes often also search for yellow top tubes. Cap colours are manufacturer naming, as the records above show (“grey cap-white ring”, “grey cap-black ring”, “gray stopper”), and “yellow” is used for more than one tube type. In the FDA-supplied AccessGUDID data (openFDA, checked 2026-10-31) two yellow-labelled additive systems appear. BD Vacutainer ACD Solution A (8.5 mL) and ACD Solution B (6.0 mL) tubes carry “YEL” in the product description and the GMDN term “Evacuated blood collection tube IVD, anticoagulant”; ACD stands for acid citrate dextrose. The BD Vacutainer tube for microbiological studies (description “TUBE SPS … YEL BC”, 3.32 mL) carries the GMDN term “Evacuated blood collection tube IVD, anticoagulant/cell preservative”; SPS in the description refers to sodium polyanethol sulfonate. A gray tube (sodium fluoride and potassium oxalate) is therefore a different additive system from either yellow tube, and only the product’s own labelling should be used to match colour to contents. For the light blue top tube see blue top tube additive.
Yellow also appears as a ring or secondary colour on other tubes. Greiner Bio-One VACUETTE records describe, for example, lithium heparin separator tubes as “green cap-yellow ring” and serum separator tubes as “black cap-yellow ring” or “red cap-yellow ring”, and a Cardinal Health Corvac serum separator tube has a “Red/Yellow Stopper”. A yellow ring or stopper element does not by itself identify a yellow top tube.
Gray top tube versus yellow top tube
| Gray top tube | Yellow top tube (as listed) | |
|---|---|---|
| Additives named in the record | Sodium fluoride and potassium oxalate | ACD solution (ACD Solution A and B tubes) or SPS (microbiological tube) |
| GMDN term in record | Anticoagulant/antiglycolytic | Anticoagulant (ACD); anticoagulant/cell preservative (SPS) |
| Cap colour wording | “grey cap”, “gray stopper” | “YEL” in the BD product descriptions |
Safe use and handling basics
The GMDN definition describes the tube as single-use, so a tube is used once and not reused or refilled. Order of draw, mixing and storage follow the tube manufacturer’s instructions for use and your laboratory’s procedures; this page does not give collection steps. A comparison of all common tube colours is in blood draw tube colors. A broader checklist of tubes and supplies is in the phlebotomy lab supply checklist, a different additive system is described in PAXgene tube, and tube standardization across sites is covered in specimen collection kit standardization in multi-site trials.
Common mistakes
- Assuming every gray cap means the same additive amounts. The records above list 5mg/4mg, 12.5/10 mg and 25/20 mg for different products.
- Treating cap colour as a standard. Colour descriptions in registered records are manufacturer-specific.
- Matching a yellow tube to its contents by colour alone instead of reading the product label; yellow can mean ACD or SPS, and a yellow ring appears on unrelated tubes.
Frequently asked questions
What is in a gray top tube?
Sodium fluoride and potassium oxalate. The FDA-supplied product records describe these tubes as “Sodium Fluoride / Potassium Oxalate”, with potassium oxalate as the anticoagulant and sodium fluoride as the antiglycolytic agent.
Is the additive amount the same in every gray tube?
No. The listed products show 5mg/4mg (BD), 12.5 mg sodium fluoride with 10 mg potassium oxalate (Monoject 5 mL draw) and 25 mg with 20 mg (Monoject 10 mL draw). Check the product label.
Is a gray top tube the same as a yellow top tube?
No. A gray top tube holds sodium fluoride and potassium oxalate. In the FDA-supplied records, yellow-labelled BD tubes are ACD solution tubes (anticoagulant) or an SPS tube for microbiological studies (anticoagulant/cell preservative). Match colour to contents using the product’s own labelling.
What is in a yellow top tube?
It depends on the product. The FDA-supplied records list ACD (acid citrate dextrose) in BD Vacutainer ACD Solution A and B tubes and sodium polyanethol sulfonate (SPS) in the BD tube for microbiological studies, all described with “YEL”. Read the label of the tube in hand.
How is a gray top tube regulated in the United States?
Blood collection tubes fall under 21 CFR 862.1675 as Class II devices; product codes JKA and GIM both list that regulation.
Sources
- openFDA Device UDI API (AccessGUDID data), device records for sodium fluoride / potassium oxalate tubes and ACD Solution A: https://api.fda.gov/device/udi.json, checked 2026-10-30.
- openFDA Device Classification API, product codes JKA and GIM: https://api.fda.gov/device/classification.json, checked 2026-10-30.
- openFDA Device UDI API (AccessGUDID data), yellow-labelled records for BD Vacutainer ACD Solution A and B and the SPS tube for microbiological studies: https://api.fda.gov/device/udi.json, checked 2026-10-31.
- 21 CFR 862.1675, Blood specimen collection device: https://www.law.cornell.edu/cfr/text/21/862.1675, checked 2026-10-30.
