Are Bruises Blanchable?
No, bruises are not blanchable—this is a fundamental distinguishing feature that separates bruises (extravasated blood in tissue) from blanchable erythema (reactive hyperemia from pressure or inflammation).
Understanding the Blanch Response
Blanchable erythema occurs when blood remains within intact vessels, allowing pressure to temporarily displace the blood and cause visible blanching when compressed 1, 2.
Bruises represent extravasated red blood cells that have leaked out of ruptured vessels into the surrounding connective tissue, making them non-blanchable because the blood is no longer within compressible vessels 3.
The blanch test works by applying light finger pressure to assess whether redness disappears temporarily—if it does, the blood is still in vessels (blanchable); if it doesn't, the blood has extravasated into tissue (non-blanchable) 2.
Clinical Significance in Assessment
Non-blanchable erythema has different blood perfusion patterns than normal skin, with altered blood flow distribution profiles that can be measured using laser Doppler imaging 1.
The distinction between blanchable and non-blanchable lesions has important clinical implications—non-blanchable erythema (such as Stage I pressure ulcers) represents actual tissue damage, while blanchable erythema may be reversible 4.
In dark-skinned individuals, visual assessment of blanching can be challenging due to high melanin concentration, though spectroscopy techniques can detect blood volume changes associated with blanching regardless of skin color 5.
Practical Assessment Technique
The transparent disk method is preferred over the finger method for assessing non-blanchable erythema, as it provides more reliable observations with substantial interrater reliability 2.
When assessing a bruise, apply light pressure with a transparent disk or finger—the discoloration will persist because the blood has already extravasated into the tissue and cannot be displaced by external pressure 2.