Where Is the Radial Artery and How Do You Find It?

The radial artery runs along the thumb side of your forearm, from just below the elbow crease to the base of the thumb, and you can feel its pulse most easily at the inner wrist about a centimeter or two from the bony bump on the thumb side. That wrist spot is where nurses check your pulse, where blood is drawn for arterial blood gas tests, and increasingly where cardiologists thread catheters for heart procedures. But the radial artery is more than just a pulse-check location. Its accessible position, its connections to the hand’s backup blood supply, and the variations it shows from person to person all have real clinical consequences worth understanding.

The Course of the Radial Artery From Elbow to Hand

The radial artery typically branches off from the brachial artery at the cubital fossa, the shallow depression on the inside of your elbow. From there, it travels down the lateral (thumb-side) aspect of the forearm, running beneath the brachioradialis muscle in the upper forearm and becoming progressively more superficial as it approaches the wrist. By the time it reaches the lower third of the forearm, it sits just beneath the skin and a thin layer of connective tissue, which is why you can feel its pulsation so readily.

At the wrist, the artery passes over the radius bone and gives off a branch called the superficial palmar branch, which joins a branch from the ulnar artery to form the superficial palmar arch in the hand. The radial artery itself then curves around the wrist and crosses through a small hollow between tendons on the back of the hand known as the anatomical snuffbox. It eventually dives into the palm between the thumb and index finger, forming the deep palmar arch that helps supply blood to all five fingers.¹ This dual-arch system is an important safety net: even if one artery is blocked, the other can often keep the hand perfused.

How to Feel the Radial Pulse at the Wrist

To find the radial pulse, turn your palm face-up and look at the wrist crease closest to your hand. Place the pads of your index and middle fingers on the groove just medial to (inside of) the bony ridge on the thumb side. You should not use your thumb, because it has its own perceptible pulse that can confuse what you are feeling. Press gently but firmly. In most people, the pulse is easy to detect within a few seconds. If you press too hard, you will compress the artery shut and lose the signal entirely.

A palpable pulse at the wrist correlates with arterial diameter. A study that measured the radial artery with ultrasound found the average diameter at the standard wrist location was roughly 2.3 mm in men and about 2.0 mm in women, and that a stronger palpable pulse corresponded to a wider vessel.² Body surface area was the best single predictor of radial artery size: taller, heavier individuals tend to have larger arteries that are easier to feel. People who are slim, dehydrated, or in shock may have a faint or nearly absent radial pulse even though the artery is right where it should be.

The Anatomical Snuffbox and Distal Radial Access

There is a second place where the radial artery is accessible to the touch, and it has become increasingly important in cardiology. The anatomical snuffbox is the triangular depression you can see on the back of your hand at the base of the thumb when you extend the thumb outward. The radial artery passes through this space, and it can be punctured there for catheter-based heart procedures.

The advantage of going in at the snuffbox rather than the standard wrist spot is that the artery at that point has already sent off its superficial palmar branch. That means even if the vessel becomes blocked after a procedure, blood flow to the hand through the palmar arch is preserved. Clinical data suggest this distal approach produces fewer puncture-site complications and faster hemostasis because the artery is very superficial and sits right on top of bone, making it easy to compress afterward.³ The downside is that the artery there is about 12% narrower than at the standard wrist site, so threading a catheter through can be more technically demanding.²

Not Everyone’s Radial Artery Is in the Same Place

Textbook anatomy describes the radial artery branching off the brachial artery at the elbow, but a meaningful fraction of people have a variant. A large meta-analysis estimated the global prevalence of radial artery variants at roughly 12%, with women showing a higher rate (about 18%) than men (about 3%).⁴ European populations had a higher prevalence than Asian populations in the same analysis.

A cadaver study that examined 200 limbs found the standard origin at the cubital fossa in about 85% of cases. In the remaining 15%, the radial artery branched off higher up: from the upper, middle, or lower portions of the brachial artery, or even from the axillary artery in the armpit.⁵ Another study of 120 limbs found a high origin in about 9% of cases, with the artery sometimes branching directly from the axillary artery and sometimes from the upper brachial artery.⁶

Course variations matter too. Tortuosity in the distal forearm was the most common course variant in the cadaver study, followed by a superficial course that crosses in front of the bicipital tendon at the elbow.⁵ For a person simply checking their pulse, these variants are invisible. But for a surgeon harvesting the artery for bypass grafting or a cardiologist navigating a catheter, an unexpected tortuous segment or an unusual branching point can change the game plan entirely.

Embryological research shows that these variants are not random defects but traces of normal fetal development. The arterial system in the arm starts as a web of tiny capillaries. During weeks five through eight of gestation, selected channels enlarge while others regress, and the definitive radial, ulnar, and interosseous arteries emerge in a proximal-to-distal sequence. Variations occur when parts of the initial capillary network that would normally disappear instead persist and enlarge.⁷

Checking Collateral Circulation With the Allen Test

Before any procedure that might compromise the radial artery, clinicians want to confirm that the hand has adequate backup blood supply through the ulnar artery. The modified Allen test is the traditional bedside tool for this. You clench your fist while someone compresses both the radial and ulnar arteries at the wrist, then open your hand and the examiner releases the ulnar artery. If the palm flushes with color within a few seconds, the ulnar supply is sufficient. A delayed or absent return suggests poor collateral flow and is typically a red flag for radial artery procedures.

The test is simple and costs nothing, which is why it remains widely used as a screening step before radial artery access or harvest.⁸ But its accuracy has legitimate critics. A recent study examining whether the Allen test’s reperfusion time reliably reflects the dominant vessel in the forearm found no significant correlation between artery size and the time it took blood flow to return.⁹ The authors concluded that relying on the Allen test alone could underestimate or overestimate collateral flow. When the test is abnormal, supplementing it with Doppler ultrasound gives a more reliable picture.⁸ Abnormal results are also more common in older adults, a population that is more likely to have diminished arterial compliance.

How Medicine Uses the Radial Artery

The radial artery’s accessibility makes it one of the most frequently accessed arteries in medicine, used for at least three distinct purposes.

The most routine use is arterial blood gas sampling. When a doctor needs to measure the oxygen and carbon dioxide levels in your blood, venous blood is not accurate enough. A needle into the radial artery at the wrist provides the arterial sample needed. This is typically quick but can be painful, and interestingly, a randomized trial found that local lidocaine injection beforehand did not reduce the median pain of the puncture compared with no anesthetic.¹⁰ Patient anxiety appeared to amplify the perceived pain more than the physical puncture itself did.

In intensive care, critically ill patients often need continuous blood pressure monitoring and frequent blood draws, which means an arterial catheter rather than repeated needle sticks. The radial artery is the preferred site for this catheter, again because of its superficial position and robust collateral hand circulation.¹¹

The third and fastest-growing use is cardiac catheterization. Cardiologists have traditionally accessed the heart through the femoral artery in the groin, but radial access has largely overtaken the femoral route for coronary angiography and stenting. A systematic review comparing the two found that radial access produced about 80% fewer entry-site complications than femoral access, with similar rates of major adverse cardiac events, although the radial approach had a higher procedural failure rate in earlier studies.¹² A separate randomized trial that directly compared radial, brachial, and femoral approaches found zero major entry-site complications with the radial route, compared with about 2% for each of the other two.¹³ Patients also prefer it because they can sit up and walk immediately afterward instead of lying flat for hours with groin pressure.

The Radial Artery as a Bypass Graft

Beyond being an access point, the radial artery can be surgically harvested and used as a bypass conduit in coronary artery bypass grafting. A five-year follow-up study found that radial artery grafts remained open in about 98% of cases, compared with roughly 86% for saphenous vein grafts taken from the leg.¹⁴ A patient-level meta-analysis published in the New England Journal of Medicine confirmed the advantage, showing the radial artery graft was associated with about half the risk of graft occlusion compared with vein grafts at a mean follow-up of roughly four years.¹⁵

The advantage is not unconditional. An eight-year study found the gap between radial and vein graft patency narrowed over time and was no longer statistically significant at the eight-year mark. Radial grafts performed worse when the target coronary vessel was only mildly narrowed (less than 75% blockage) and in patients with peripheral vascular disease.¹⁶ Surgeons consider these factors when deciding which conduit to use and where to take it from.

When the Radial Artery Is Hard to Find

Sometimes locating the radial artery by touch alone is difficult. Obese patients, those with low blood pressure, people with arterial disease, and patients on vasopressor medications can all have a weak or absent palpable pulse. In these cases, ultrasound guidance has become a reliable backup. A systematic review covering both adults and children found strong evidence that ultrasound improved first-attempt success rates for radial artery cannulation compared with the traditional palpation technique.¹⁷

A prospective trial comparing ultrasound short-axis, long-axis, and palpation-only techniques for radial catheter placement found first-attempt success rates of roughly 87%, 77%, and lower for palpation alone, with the short-axis ultrasound method also achieving the fastest average cannulation time at about 35 seconds versus 52 seconds for palpation.¹⁸ For routine blood gas draws in patients with a strong pulse, ultrasound may not help much: one trial in easy-to-palpate patients found no advantage in pain or satisfaction.¹⁹ But in difficult cases, ultrasound nearly tripled the first-attempt success rate and roughly halved the puncture time.²⁰

Radial Artery Access in Children

Infants and small children present a specific challenge. Their radial arteries are tiny, and the pulse is often hard to feel even under ideal conditions. A meta-analysis of randomized controlled trials in pediatric populations found that ultrasound guidance increased both first-attempt success and overall success rates compared with palpation alone.²¹ First-pass success is especially valuable in this group, because failed attempts cause hematomas that further compress the already small vessel and make subsequent tries even harder.²²

What Can Go Wrong After Radial Artery Procedures

The most common significant complication of transradial catheterization is radial artery occlusion, where the artery clots shut afterward. Reported incidence varies widely. A meta-analysis of over 31,000 patients found that about 8% of arteries were occluded within 24 hours of the procedure, dropping to roughly 5.5% at follow-ups beyond one week as some clots resolved on their own.²³ Most people with radial artery occlusion never develop hand ischemia, because the ulnar artery and the palmar arches keep the hand supplied. But occlusion does mean the artery cannot be used for future procedures or as a surgical conduit.²⁴

Higher doses of blood-thinning medication during the procedure and shorter compression times afterward were the most effective strategies for reducing occlusion risk.²³ Independent risk factors for occlusion in one recent study included prior coronary artery disease, multiple puncture attempts, a puncture that took longer than 15 minutes, and arterial spasm during the procedure.²⁵

Rarer complications include pseudoaneurysm (a contained leak at the puncture site) and arterial perforation. Pseudoaneurysms after radial access occur in about 0.05% of cases, a tiny fraction of the 0.2% to 3% rate seen with femoral artery access.²⁶ Compartment syndrome and perforation are rare but can require surgical intervention if not caught quickly.²⁷

Wearable Sensors and the Radial Pulse

Outside the hospital, the radial artery is attracting attention from engineers building wearable health monitors. The wrist is already the dominant location for consumer fitness trackers, but most of those devices use optical sensors that estimate heart rate by detecting blood volume changes in tiny capillaries. A newer generation of devices aims to capture the actual pressure waveform of the radial artery pulse, which contains much richer physiological information. The shape of that waveform reflects arterial stiffness, cardiac output, and vascular resistance, and researchers are developing methods to estimate central blood pressure from a single radial pulse recording.²⁸

One challenge is building sensors flexible and sensitive enough to pick up the subtle pressure variations. Recent prototypes using piezoelectric materials and structured conductive membranes have demonstrated the ability to capture fine details of the radial pulse waveform, including the dicrotic notch that marks the closing of the aortic valve.²⁹ The goal is a wrist-worn device that could serve as a screening tool for cardiovascular disease in everyday life, although the technology remains largely at the research stage. Positioning the sensor precisely over the radial artery turns out to be a nontrivial engineering problem, because even a millimeter of displacement from the optimal spot degrades the signal.³⁰ Anyone who has worn a wrist-based heart rate monitor and gotten suspicious readings during exercise has bumped into a consumer version of this same problem.