How to read an insulin syringe

Start with the numbers printed on the barrel. Then count the small lines between two numbers, so you know what each line is worth.

• 0.3 mL syringe (30 units): each small line is 1 unit, with a longer line every 5.
• 0.5 mL syringe (50 units): each small line is 1 unit, with a longer line every 5.
• 1 mL syringe (100 units): each small line is 2 units, with a longer line every 10.

These are the lines Claritide draws. Markings can differ between makers, so count the lines on your own syringe before you trust one.

To read a draw, look at the plunger tip, the dark rubber part inside the barrel. Line up the edge of the tip closest to the needle with your mark. The instructions for the approved tirzepatide vial measure the same way: the plunger tip goes to the line.

You can only set the plunger on a line. On a 1 mL syringe, an odd number like 7 falls halfway between the 6 and 8 lines. A smaller syringe, with a line for every unit, puts it right on a line.

When a number lands between two lines, there are three ways out:

• Round to the nearest line.
• Use a smaller syringe, with a line for every unit.
• For a vial you mix yourself, change the amount of bac water so the dose lands on a line.

Rounding changes the dose a little, and on a small dose a little is a lot. Rounding 2.5 units down to 2 is a fifth less.

Claritide's free calculator rounds to the nearest line. On an exact tie it rounds down, so it never tells you to draw more than you asked for. It also warns when a draw is under 2 units, where one line is a big share of the dose. If rounding matters for your dose, ask your prescriber or pharmacist how they want it handled.

All three sizes are U-100, so a unit is the same amount of liquid on each. What changes is the room each unit gets. A 0.3 mL syringe has only 30 units along its barrel, so each one gets its own line and more space. A 1 mL syringe fits 100 units, with a line every 2.

So a small draw is easier to read on a small syringe. A draw of more than 30 or 50 units needs a bigger barrel, because it will not fit. FDA has linked dosing mistakes to small doses, such as 5 units, drawn with a 1 mL syringe. It asks prescribers and compounders to hand out a syringe size that fits the dose.

Four slips are worth knowing before they happen:

• One extra zero. 8 units and 80 units are both easy to say, type and misread. On a 1 mL syringe, 8 units sits just short of the 10 line. 80 units fills most of the barrel. If a draw looks much bigger or smaller than last time, stop and check.
• Counting lines as units on a 1 mL syringe. There, each small line is 2 units, so counting 10 lines draws 20 units.
• Mixing up mL and units. 0.1 mL is 10 units, not 1.
• Picking up a U-40 syringe. Syringes for pet insulin are U-40, where 40 units fill 1 mL. Each of their units holds 2.5 times the liquid of a U-100 unit. Check that the box and the barrel both say U-100.

FDA has reported people taking 5 to 20 times the dose they meant to, after mix-ups between mL, mg and units. Each of these slips is easy to catch once you know it is there.

While the needle is still in the vial, yes. Push the plunger slowly back up until its tip sits on your line. The instructions for the approved tirzepatide vial work the same way. Draw a little past the line, tap any air bubbles to the top, then push back up to it.

Once a needle has been in your skin, it never goes back into the vial. Use a new needle and syringe for every shot. CDC tells health care providers to use a new needle and syringe every time they draw from a multi-dose vial.

Already injected more than you meant to? The tirzepatide medication guide says to call your healthcare provider or Poison Help right away, at 1-800-222-1222. Or go to the nearest emergency room.