The GTT medical abbreviation most often means drop, the unit used for eye, ear and some oral liquid medicines, and gtts is the plural, drops. Both come from the Latin gutta, drop, with guttae as the plural.
In hospital speech and notes, gtt has a second life as shorthand for a continuous intravenous drip, as in "heparin gtt" or "insulin gtt." And in lab and pregnancy care, GTT in capitals usually means glucose tolerance test. Context sorts these out quickly: a number of drops next to an eye abbreviation, a drug name followed by a rate, or a lab order. This page walks through each use with real looking lines and notes where it sits among other prescription abbreviations.
At a glance
Stands for
Drop (gtt) or drops (gtts)Latin origin
Gutta, drop; plural guttaeWritten as
gtt, gtts, GTT, gtt.Other meanings
Continuous IV drip (heparin gtt); glucose tolerance test (lab)Where you see it
Eye and ear drop orders, ICU notes, lab and prenatal ordersRelated terms
OU, OS, OD for eyes; mL/hr for drip ratesPlural or forms
gtts for drops; gtt alone for one drop or a drip
What the GTT medical abbreviation means on a drop order
On a prescription for eye drops, ear drops or a few oral liquids, gtt is the unit of measure. "1 gtt" means one drop, and "2 gtts" means two drops. The order then names where the drops go and how often. A pharmacist turns that into plain language on the label, such as "Instill 1 drop into each eye twice daily."
Drops are small and vary a bit by bottle, which is why oral liquids are usually measured in mL instead. Eye and ear products, however, are designed around the drop, so gtt remains the natural unit for them.
Decoding drop orders
| Order | Meaning |
|---|---|
| Timolol 0.5% 1 gtt OU BID | One drop in both eyes twice a day |
| Prednisolone acetate 1% 1 gtt OS QID | One drop in the left eye four times a day |
| Ofloxacin otic 5 gtts AD BID | Five drops in the right ear twice a day |
Notice how much rides on the two letters after gtt. OD, OS and OU (eyes) and AD, AS and AU (ears) are on the ISMP error-prone list because they get swapped, so many labels write right eye, left ear and so on in full. These lines show format only.
Gtt as a drip: heparin gtt, insulin gtt
In intensive care and hospital wards, clinicians often say or write "gtt" for a medicine running continuously through an IV pump. The idea comes from the old drip chamber, where fluid falls drop by drop. Heparin is so often run this way that staff shorten it further to hep gtt.
ICU progress note: "Heparin gtt at 18 units/kg/hr, titrate per protocol; insulin gtt off since 0600." Here gtt means continuous infusion, not drops. Note that units is written in full, since the letter U for units is banned in orders.
Drip orders give a rate, usually in mL per hour or a dose per kilogram per hour. If you read "drip" or "gtt" next to a drug name and a rate, it means an ongoing infusion.
Drop factor: gtt/mL on IV tubing
Students meet gtt again in IV math. Gravity IV tubing is labeled with a drop factor, written gtt/mL, that tells how many drops make one milliliter. Macrodrip sets commonly deliver 10, 15 or 20 gtt/mL, and microdrip sets deliver 60 gtt/mL.
Nurses use the drop factor to set a manual drip rate in drops per minute when a pump is not used. For example, 1,000 mL over 8 hours with a 15 gtt/mL set works out to about 31 drops per minute. Most hospitals now run IV fluids on pumps, but the calculation still appears on exams.
GTT as a glucose tolerance test
In lab orders and prenatal care, GTT in capitals usually means glucose tolerance test, often written OGTT for oral glucose tolerance test. The person drinks a measured glucose solution, and blood sugar is checked at set times afterward. It is used to diagnose gestational diabetes and sometimes other forms of diabetes.
The giveaway is that it shows up as a test, not a dose: "1 hr GTT ordered at 26 weeks" or "3 hour GTT results pending." Each lab sets its own cutoffs and preparation instructions, such as fasting beforehand.
Gtts pharmacy abbreviation tips for readers and students
- Lowercase gtt or gtts beside a number and a body site almost always means drops.
- Gtt next to a drug and a rate per hour means a continuous drip.
- Capital GTT in a lab list or pregnancy note means glucose tolerance test.
- If the site letters after gtt are unclear, the plain words on the pharmacy label are the version to follow.
When writing, many teachers suggest spelling out drop or drops on anything a patient will read.
This page covers general meanings only. How many drops to use, how to put them in and how to space two different eye drops are details your pharmacist or eye care clinician can show you.
Frequently asked questions
What does gtt mean on eye drops?
Gtt means drop, so 1 gtt is one drop. The letters after it, such as OU or OS, tell which eye, and the frequency term says how often.
What is the difference between gtt and gtts?
Gtt is singular, one drop, and gtts is plural, drops. Both come from the Latin gutta.
What does heparin gtt mean?
It means heparin is running as a continuous IV infusion, a drip, usually on a pump at a set hourly rate. In that setting gtt does not mean drops.
What does GTT mean in pregnancy?
In prenatal care, GTT usually means glucose tolerance test, a blood sugar test after drinking a glucose solution. It is used to check for gestational diabetes.
What does 15 gtt/mL mean on IV tubing?
It is the drop factor: 15 drops from that tubing equal one milliliter. Nurses use it to calculate drip rates when fluid runs by gravity.