What does TDS mean on a prescription?

Three times a day. The US equivalent is TID.

As needed — from the Latin pro re nata. There is usually still a limit on how much and how often, shown on the label.

What does 1/52 mean on a hospital letter?

One week. The number after the slash is the unit: /7 days, /52 weeks, /12 months.

ABBREVIATIONS

Discharge summary abbreviations: what TDS, BD, PRN and the rest mean

Discharge summaries are written for other clinicians, so they use shorthand: OD means once a day, BD twice a day, TDS three times a day, QDS four times a day, PRN as needed, PO by mouth, and 1/52 one week. The list below covers the abbreviations people most often ask about.

Why it’s confusing

Many abbreviations come from Latin (bis die, ter die sumendum, pro re nata), and UK and US hospitals use different ones for the same thing — UK BD and TDS, US BID and TID.

The same letters can mean different things in different contexts, and these documents are often the only written record of what changed with your medicines.

How to read it

How often: OD or QD — once a day; BD or BID — twice a day; TDS or TID — three times a day; QDS or QID — four times a day; PRN — as needed; nocte — at night; mane — in the morning; stat — straight away (usually given in hospital).

How it is taken: PO — by mouth; IV — into a vein; SC or SubQ — under the skin; IM — into a muscle; PR — rectally; inh — inhaled; top — on the skin.

Time: 1/7 — one day; 1/52 — one week; 1/12 — one month. So “review in 6/52” means in six weeks.

Notes: PMH — past medical history; Hx — history; Dx — diagnosis; Rx — treatment or prescription; c/o — complaining of; NAD — no abnormality detected; NBM — nil by mouth; TTO or TTA — medicines to take home; f/u — follow-up.

Scans are often shortened too — CXR for chest X-ray, CT, MRI, US or USS for ultrasound. For the wording inside a radiology report itself, see Radily’s phrase guides.

What it does not mean

That an abbreviation’s meaning is always the same. If one is unclear on your own summary, ask the ward, your GP or a pharmacist.
That PRN means “take as much as you like”. A PRN instruction usually still has a maximum — check the label or ask the pharmacist.
That the summary replaces the instructions on your medicine labels. Follow the labels and ask if they differ.

Where you’ll see it

Hospital discharge summaries and letters to your GP.
Medicines lists, prescription labels and clinic letters.

Questions worth asking

Ask the ward or your pharmacist

What does this abbreviation mean on my summary?
Which medicines are new, changed or stopped?
Is there a maximum for my as-needed medicine?

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Common questions

What does TDS mean on a prescription?: Three times a day. The US equivalent is TID.
What does PRN mean?: As needed — from the Latin pro re nata. There is usually still a limit on how much and how often, shown on the label.
What does 1/52 mean on a hospital letter?: One week. The number after the slash is the unit: /7 days, /52 weeks, /12 months.

Sources

Reading a scan report rather than a blood test or letter? Radily’s radiology report phrase guides explain the wording radiologists use.