A suture pack carries five pieces of information you need to read correctly: size, material, thread length, needle and sterility data. This guide explains the USP size system, from 7-0 up to sutures thicker than 0, how it maps to metric size, the difference between absorbable and non-absorbable sutures, how needles are described and what to check on the pack before you order.
In short
- For sizes ending in “-0”, a higher number means a thinner thread: 7-0 is thinner than 2-0.
- Above 0 the scale goes up: 1, 2, 3 and 4 are progressively thicker.
- Metric size gives the minimum diameter in tenths of a millimeter: metric 1.5 means at least 0.15 mm.
- Absorbable in the catalog: polyglycolic acid (PGA), polyglactin 910, polydioxanone; non-absorbable: silk, nylon (polyamide), polypropylene.
- The needle is described by curvature (1/2 or 3/8 circle), point (round, cutting, Tapercut) and length in mm.
How to read USP sizes
The USP system, from the United States Pharmacopeia, starts at size 0. Thinner sutures are written 2-0, 3-0, 4-0 and so on, sometimes as 2/0, 3/0: the higher the first number, the thinner the thread. Above 0, thick sutures are numbered 1, 2, 3 and 4. The USP monographs require the size on the suture label to be given both as a metric size and as a USP size.
The metric size, shown on some packs as “EP” or “Metric”, reads directly: the number is the minimum diameter of the thread in tenths of a millimeter. A metric 2 suture is at least 0.20 mm thick, a metric 1.5 suture at least 0.15 mm.
| USP size | Metric size | Minimum diameter | Materials in the catalog |
|---|
| 7-0 | 0.5 | 0.05 mm | not in the catalog |
| 6-0 | 0.7 | 0.07 mm | PGA |
| 5-0 | 1 | 0.10 mm | PGA, silk, polyamide, polypropylene |
| 4-0 | 1.5 | 0.15 mm | PGA, polyglactin, silk, nylon, polypropylene |
| 3-0 | 2 | 0.20 mm | PGA, polydioxanone, silk, nylon, polyamide, polypropylene |
| 2-0 | 3 | 0.30 mm | PGA, polydioxanone, silk, nylon, polypropylene |
| 0 | 3.5 | 0.35 mm | PGA, polydioxanone, silk, polypropylene |
| 1 | 4 | 0.40 mm | PGA, polydioxanone, silk, polypropylene |
| 2 | 5 | 0.50 mm | PGA, silk |
| 3 and 4 | 6 | 0.60 mm | PGA (USP 3) |
The diameters are those in the USP tables for synthetic absorbable and non-absorbable sutures; each size has a range, and the table shows its lower limit. Collagen (catgut) sutures have a separate table: for them the same USP size corresponds to a larger metric number, so 2-0 means metric 3.5, not metric 3.
Absorbable or non-absorbable
The US Pharmacopeia defines an absorbable suture as a sterile strand that can be absorbed by living tissue, and a non-absorbable suture as one that resists the action of living tissue. Which suture is used for a given wound or procedure is the doctor’s decision; for purchasing, what matters is the material, the construction and the sizes you need.
| Material | Type | Construction | What the catalog sheet states |
|---|
| Polyglycolic acid (PGA) | absorbable | braided multifilament, coated | 70–80% of strength retained in the first 14 days, 50% at 21 days, complete absorption usually within 60–90 days |
| Polyglactin 910 | absorbable | braided multifilament, coated | copolymer of 90% glycolide and 10% L-lactide |
| Polydioxanone (PDO) | absorbable | monofilament | synthetic violet thread |
| Silk | non-absorbable | braided multifilament, silicone-coated | moderate tissue reaction |
| Nylon (polyamide 6.0) | non-absorbable | monofilament | blue thread; polyamide is also in the catalog as a black multifilament |
| Polypropylene | non-absorbable | monofilament | blue thread |
The PGA product sheets in the catalog also state the limits of use: they are intended for approximation and ligation of soft tissue, including plastic and ophthalmic procedures, but not for cardiovascular or neurological tissue. Read the exact indications and contraindications in each product’s instructions, because they differ from one suture to another.
Absorbable and non-absorbable sutures
Monofilament or multifilament
A monofilament suture is made of a single fiber, a multifilament suture of several fibers braided or twisted together. The construction is shown on the pack and on the data sheet. The braided sutures in the catalog are coated: PGA with a blend of caprolactone and calcium stearate, silk with silicone. The USP monograph allows non-absorbable sutures to be treated to reduce capillarity, the tendency to wick fluid along the fibers.
The needle: curvature, point and length
- Curvature is given as a fraction of a circle. A 1/2 needle forms half a circle, a 3/8 needle three eighths of a circle. Both are available in the catalog.
- Length is given in millimeters and measured along the body of the needle, by manufacturers’ convention. In the catalog, needles range from 13 to 40 mm.
- Point and cross-section:
- round (RB for “round body”, or taper point): round body that passes through tissue without cutting edges;
- triangular or cutting: triangular cross-section with cutting edges;
- reverse cutting (RC): also triangular in cross-section, labeled this way on the polyamide and polydioxanone sheets in the catalog;
- Tapercut: round body with a cutting tip.
- Needle attachment: the sheets use the term “atraumatic needle”, meaning the needle is fixed into the end of the thread, without an eye, so only a single strand passes through the tissue.
Some manufacturers summarize these details in a code printed on the pack, and the codes differ from one manufacturer to another. In the catalog of the manufacturer Assut, for example, HR-22 means a 1/2-circle needle (H) with a round body (R) and a length of 22 mm, and an added letter G marks the heavier version of the needle. When you switch supplier, compare curvature, point and length, not the code.
Thread length and packaging
The needled sutures in the catalog are 70, 75 or 90 cm long, and those without a needle, used for example for ligatures, 150 cm; for veterinary use there are also 25 m reels. Many sutures are sold in boxes of 12 packs, and the exact quantity is given in the product name or sheet. Thread color also differs: PGA is dyed violet, with an undyed version, silk and multifilament polyamide are black, and the nylon and polypropylene in the catalog are blue; the manufacturers’ descriptions link color to the visibility of the thread in the surgical field. When comparing prices, work from the price per pack, not per box.
What to check on the pack and the box
Take as examples the 75 cm PGA 4-0 suture with a 16 mm 3/8 cutting needle or the silk 3-0 suture with a 22 mm 1/2 round needle. On the pack and box, look for:
- Size, as USP and metric size.
- Material and construction: monofilament or multifilament, coated or not, thread color.
- Thread length in centimeters and the number of packs in the box.
- Needle: curvature, point, length in millimeters and the manufacturer’s code.
- Sterility and method: “STERILE EO” for ethylene oxide or “STERILE R” for irradiation.
- Lot and expiry date, at least year and month, plus the symbols for single use, “do not resterilize” and “do not use if package is damaged”.
- CE mark followed by the notified body number, present on sterile devices.
The USP monographs require each pack label to state the material, size, construction and length of the suture, whether it is sterile or non-sterile, the type of needle, the number of sutures, the lot and the manufacturer. Regulation (EU) 2017/745 adds, for sterile devices, the sterile condition and sterilization method and the date until which the device can be used safely.
Common ordering mistakes
- Confusing 3-0 with 3. 3-0 is a thin suture, metric 2, while USP 3 is a thick one, metric 6; the only difference is the dash and the zero.
- Comparing catgut with synthetic sutures by metric number. At the same USP size, collagen sutures have a different metric number from synthetic ones.
- Ordering by thread and size only. The same thread in the same size with a different needle is a different product: specify the needle curvature, point and length.
- Forgetting the thread length. A 75 cm needled suture and a 150 cm suture without a needle are different products, meant for different tasks.
- Not checking the expiry date on large orders: sterile sutures have an expiry date, and stock is rotated by it.
Instruments for suturing
To place and remove sutures you need a needle holder, for example Mayo-Hegar or Olsen-Hegar, the latter with built-in scissors, Adson-type surgical forceps and scissors. The 9.5 cm PRIMA Littauer scissors have a notch designed for cutting and removing sutures; like any reusable instrument, they are used again only after cleaning, disinfection and sterilization. For wound closure without thread there are sterile skin staplers with 35 staples, staple removers and sterile skin closure strips.
All sutures, by material and size, are in the surgical sutures category, divided into absorbable sutures and non-absorbable sutures.
Frequently asked questions
What does 4-0 mean on a suture?
4-0 (also written 4/0) is the suture size in the USP system. It corresponds to metric size 1.5, a diameter of at least 0.15 mm, and is thinner than 3-0.
Which is thicker, 2-0 or 3-0?
2-0. For sizes ending in “-0”, a higher number means a thinner thread: 2-0 corresponds to metric size 3 (at least 0.30 mm) and 3-0 to metric size 2 (at least 0.20 mm).
What does “metric 2” or “EP 2” on the pack mean?
It is the metric size: the minimum diameter of the thread in tenths of a millimeter, here 0.20 mm. For synthetic and non-absorbable sutures it corresponds to USP 3-0; for collagen (catgut) sutures the correspondence is different.
Which sutures are absorbable?
In the catalog, polyglycolic acid (PGA), polyglactin 910 and polydioxanone sutures are absorbable. Silk, nylon (polyamide) and polypropylene sutures are non-absorbable.
What do 1/2 and 3/8 mean on a suture needle?
They show the needle curvature as a fraction of a circle: a 1/2 needle forms half a circle, a 3/8 needle three eighths of a circle. The needle length in millimeters is given next to the curvature.
What is the difference between a round and a cutting needle?
A round needle (RB or taper point) has a round body and passes through tissue without cutting edges. A cutting needle has a triangular cross-section with cutting edges; the Tapercut type combines a round body with a cutting tip.
