PR has several different meanings in medicine, and the one that applies depends entirely on the context. The most common uses are “per rectum” (a route for administering medication or a type of physical exam), “pulse rate” (a vital sign), “progesterone receptor” (relevant in breast cancer), and “PR interval” (a measurement on a heart tracing). Less frequently, it can stand for “partial response” in cancer treatment or “pulmonary regurgitation” in cardiology.
Per Rectum: Medication Route and Exams
In prescriptions and medication orders, PR stands for “per rectum,” meaning a drug is meant to be given through the rectum rather than swallowed or injected. Suppositories and certain enemas are common examples. You might see this abbreviation on a prescription label or in discharge instructions.
PR also shows up when doctors refer to a “PR exam,” which is a digital rectal examination. During this exam, a clinician visually inspects the area around the rectum and then uses a gloved, lubricated finger to feel for abnormalities inside. It’s used to evaluate symptoms like abdominal pain, constipation, rectal bleeding, or changes in bowel habits. It also plays a role in screening for prostate and colorectal cancers, since the examiner can feel for unusual lumps or masses and check a stool sample for hidden blood.
Pulse Rate: A Basic Vital Sign
On a hospital monitor, bedside display, or pulse oximeter, PR typically means pulse rate. A normal resting pulse rate for adults falls between 60 and 100 beats per minute. Your actual number varies with age, fitness level, medications, stress, sleep quality, and even body position.
Pulse rate and heart rate are related but not identical. Heart rate is measured directly from the heart’s electrical activity using an ECG. Pulse rate is measured at a peripheral point like your fingertip or wrist, where it picks up the mechanical wave of blood pushing through your arteries. In most healthy people the two numbers are nearly the same, but they can diverge. Breathing, for instance, creates small fluctuations in the pulse wave at your fingertip that don’t appear on an ECG tracing. For routine monitoring, the difference rarely matters, but in patients with pacemakers or certain heart conditions, clinicians rely on the ECG signal for more precise readings.
PR Interval: Heart Rhythm on an ECG
When reading an electrocardiogram (ECG or EKG), the PR interval is the stretch of time between the moment the upper chambers of the heart (atria) start their electrical signal and the moment the lower chambers (ventricles) begin theirs. It normally lasts between 120 and 200 milliseconds.
A PR interval shorter than 120 ms can suggest the electrical signal is taking a shortcut through the heart, which happens in conditions like Wolff-Parkinson-White syndrome. A PR interval longer than 200 ms points to a delay in conduction, commonly called a first-degree heart block. Both findings show up on routine ECGs and help clinicians decide whether further evaluation is needed.
Progesterone Receptor: Breast Cancer Testing
In oncology, PR stands for progesterone receptor. When a breast tumor is biopsied, pathologists test whether the cancer cells have receptors for the hormones estrogen (ER) and progesterone (PR). Roughly 70% of breast cancers are hormone receptor-positive, meaning the cells use one or both of these hormones to grow.
PR status matters because it influences both prognosis and treatment. Tumors that are ER-positive and PR-positive tend to respond well to hormone-blocking therapies and generally carry a better outlook. Tumors that are ER-positive but PR-negative are associated with a higher risk of recurrence and tend to respond less well to hormone therapy alone, so chemotherapy is more likely to be added to the treatment plan. About 83% of hormone receptor-positive breast cancers are ER-positive/PR-positive, while around 15% are ER-positive/PR-negative.
A small subset, roughly 2%, are ER-negative but PR-positive. These are more often found in younger patients (under 49) and have outcomes that fall between the ER-positive group and the fully hormone receptor-negative group. Your pathology report will list PR status as positive or negative, sometimes with a percentage score indicating how many cancer cells expressed the receptor.
Partial Response: Cancer Treatment Outcomes
In clinical trials and treatment monitoring for solid tumors, PR can mean “partial response.” Under the standard criteria used by oncologists and the FDA, a partial response is defined as at least a 30% decrease in the combined size of target tumors compared to baseline measurements. It means the cancer is shrinking with treatment but hasn’t disappeared completely. The other categories on this scale are complete response (tumor gone), stable disease (no significant change), and progressive disease (tumor growing).
Pulmonary Regurgitation: A Heart Valve Issue
In cardiology, PR can refer to pulmonary regurgitation, a condition where blood leaks backward through the pulmonary valve from the pulmonary artery into the right ventricle during the resting phase of each heartbeat. The most common causes are pulmonary hypertension and congenital heart defects, particularly tetralogy of Fallot. It also frequently develops after surgical repair of those defects.
Mild pulmonary regurgitation is common and often harmless. Severity is graded by echocardiogram based on the width of the leaking blood jet relative to the valve opening. When the jet fills more than 50% of the outflow tract, it’s classified as severe, and valve replacement may be considered if the heart chambers start to enlarge or weaken.
How to Tell Which Meaning Applies
Context almost always makes the meaning clear. If you see PR on a prescription or medication instructions, it means per rectum. On a vital signs monitor, it’s pulse rate. In a pathology or biopsy report, it refers to progesterone receptor status. On an ECG readout, it’s the PR interval. In imaging reports tracking tumor size, it likely means partial response. And in an echocardiography report, it points to pulmonary regurgitation. If your medical records use PR and you’re unsure which definition fits, the surrounding text or the specialty of the provider will almost always resolve it.