Heparin Lock Flush: 10 vs. 100 Units/mL, Why Prefilled Syringes Won, and How to Keep It Away From Therapeutic Heparin

Heparin lock flush is low-concentration heparin, typically 10 or 100 units/mL, used to keep IV catheters open. It isn't anticoagulation. Therapeutic heparin vials come in concentrations like 1,000, 5,000, and 10,000 units/mL. That's as much as a 1,000-fold difference, and some of the most notorious medication errors on record happened because a flush vial and a therapeutic vial looked alike.

So the purchasing rule is simple: buy flush in a form that can't be confused with therapeutic heparin, and store them apart. Here's why, and how.

What went wrong before?

Pennsylvania's patient safety reporting system documented the pattern in 2006 (PA PSRS, Dec 2006):

• In an Indiana hospital, heparin 10,000 units/mL vials were stocked where 10 units/mL vials belonged. Nurses used them to prepare infant line flushes, and the advisory reports three premature infants died. The vials looked very similar.
• Another report described 1,000 and 10,000 units/mL vials stored side by side, which led to a tenfold overdose that was caught and reversed.
• A third report described 5,000 units/mL heparin stocked alongside 100 units/mL flush in the same dispensing cabinet.

A 2009 AHRQ case review described an anesthesiologist who drew heparin from a 10 units/mL vial, believing it was 1,000 units/mL, because the two vials were similar shades of yellow (AHRQ PSNet, 2009).

Notice that none of these were exotic failures. They were stocking and look-alike failures. That's purchasing's territory.

What do the safety recommendations say?

Both sources land in the same place:

• Use prefilled syringes for heparin flushes. PA PSRS recommends using prefilled syringes for all heparin flushes. AHRQ's reviewer says to eliminate vials intended for catheter flushes and use manufacturer- or pharmacy-prepared syringes instead of drawing flushes from concentrated vials.
• Limit the concentrations on hand. Keep as few therapeutic concentrations in patient-care areas as you can, and tightly control or remove concentrated floor stock (PA PSRS; AHRQ).
• Separate look-alikes physically, and flag any product moved to a new location (PA PSRS).
• Double-check restocking. Have a second person, or barcode scanning, verify what goes into each bin (PA PSRS; AHRQ).

What's in a prefilled flush syringe?

As an example, one heparin lock flush product in FDA's device database is a 10 mL syringe containing a 5 mL fill of 100 USP units/mL (500 units total), labeled single-use, stored at 20°C to 25°C, and to be protected from freezing (FDA GUDID listing). That product is listed in FDA's medical device database, with a 510(k) premarket number (K133446).

The point isn't the brand. It's the format. A 10 mL flush syringe doesn't look like a 1 mL vial of therapeutic heparin, and nobody has to draw it up.

Ordering checklist

• Buy flush as prefilled syringes, not vials.
• Order by concentration and NDC. 10 and 100 units/mL flush are different products, and your clinicians or protocols decide which. Here's how NDCs work.
• Store flush and therapeutic heparin in different places, not adjacent bins.
• Never substitute across concentrations without the clinician and pharmacist signing off, and tell everyone when a product changes.
• Recheck bins after every restock. Most of the errors above started with a restock.

Order heparin lock flush from Premier

Premier Pharma supplies licensed clinics, infusion centers, surgery centers, and pharmacies, and every invoice lists the lot number and expiration date for each item. We carry heparin lock flush 100 units/mL, 5 mL in 10 mL prefilled syringes. Open a free account. Credential review typically takes 1–2 business days.

Sources

• Pennsylvania Patient Safety Reporting System. Let's Stop the Bleeding: Preventing Errors with Heparin Therapy. PA PSRS Patient Saf Advis. 2006 Dec;3(4):31.
• Vanderveen T. Vial Mistakes Involving Heparin. AHRQ PSNet WebM&M, May 2009.
• U.S. FDA / NLM. AccessGUDID: Heparin Lock Flush, USP, 100 USP units/mL, 5 mL in 10 mL syringe.