Capillary refill time (CRT) is a simple, non-invasive assessment used to check how well blood flows to the extremities. It is performed by briefly pressing on a capillary bed, such as a fingernail, until the skin turns pale, and then timing the return of color. This measurement offers a rapid indication of peripheral circulation, or the perfusion of blood to the body’s smaller vessels. The test is common in emergency and clinical settings, providing immediate feedback about circulatory status.
What Capillary Refill Measures
The capillary refill time provides an indirect assessment of peripheral perfusion, which is the blood flow to the capillary beds nearest the skin’s surface. When pressure is applied, blood is temporarily squeezed out of these tiny vessels. The time it takes for the color to return reflects the efficiency of the body’s circulatory system in refilling those capillaries.
The speed of this blood return depends on the driving pressure generated by the heart, the tone of the small arteries (arterioles), and the overall volume of circulating blood. A fast refill indicates adequate blood volume and strong blood pressure reaching the periphery. A delayed time suggests the body compensates for reduced blood volume or poor cardiac output by constricting peripheral vessels to prioritize flow to vital organs.
A prolonged refill time is an early sign of poor tissue perfusion. Measuring CRT is a rapid way to assess a person’s hydration status and overall circulatory function. It is a useful clinical indicator, but it should be used as part of a broader physical assessment, not as a standalone diagnostic tool.
Performing the Capillary Refill Test
To perform the test, the testing site, typically a fingertip, should be held at or slightly above the level of the heart to prevent results from being skewed by gravity. Select a digit free of nail polish, edema, or restrictions like a tight ring, as these interfere with the reading. For infants, the skin over the sternum or forehead is sometimes used as an alternative site.
Apply firm, moderate pressure to the nail bed or the soft pad of the finger. The pressure must be enough to cause the area to blanch, or turn white, as the blood is expelled from the capillaries. Hold this pressure consistently for at least five seconds to ensure the capillaries are fully emptied.
Immediately upon releasing the pressure, observe the blanched area and begin timing the return of the natural pink color. A stopwatch or a watch with a second hand is recommended for the most accurate measurement. The time recorded, in seconds, is the capillary refill time.
Interpreting the Results
The time it takes for the color to return is compared against established normal ranges. In a healthy adult, a capillary refill time of less than two seconds is considered normal, indicating good peripheral blood flow. Some guidelines suggest that a return to color in up to three seconds may be acceptable in certain populations.
A result of three seconds or longer is considered a prolonged or delayed capillary refill time, suggesting decreased peripheral perfusion. This delayed return indicates potential issues such as dehydration, hypovolemia, or shock. In these conditions, the body initiates vasoconstriction, narrowing peripheral blood vessels to redirect blood centrally, which slows the refill time.
A prolonged CRT is an important finding that may prompt further investigation into cardiovascular status. While the test is not a specific diagnosis, it serves as a warning sign of compromised circulation. Conversely, a very rapid refill time may suggest increased blood flow or peripheral vasodilation.
Variables That Affect Accuracy
The accuracy of the capillary refill test can be affected by several external and physiological factors that should be controlled during the assessment. Cold ambient temperatures cause the body to constrict blood vessels in the extremities, which artificially prolongs the refill time. Therefore, the test should be performed in a warm environment, ideally between 20°C and 25°C.
Poor lighting conditions make it difficult to accurately observe the moment the color returns. The patient’s age influences the result, as older individuals often have a slightly longer normal CRT due to vascular changes. Edema or thick nail polish can also interfere with obtaining a reliable reading.