**Question:** Which is not true regarding the colour of bruise -

A. A bruise appears immediately after an injury
B. The colour of a bruise changes over time due to blood breakdown products
C. The colour of a bruise is primarily determined by the presence of blood in the area
D. A bruise always resolves completely within a week

**Core Concept:**
Bruises are a common clinical finding resulting from blood leakage and accumulation beneath the skin following tissue trauma. The colour change of a bruise reflects the degradation of blood breakdown products, primarily hemoglobin, which is catalysed by enzymes like heme oxygenase-1 (HO-1). The process begins with the immediate release of heme from damaged red blood cells, followed by the production of biliverdin, bilirubin, and eventually iron.

**Why the Correct Answer is Right:**
Option D is incorrect as the resolution time of a bruise depends on the extent of tissue damage and the individual's healing capabilities. In general, smaller bruises can resolve within a week, but larger or more severe bruises may take weeks to months to heal.

**Why Each Wrong Option is Incorrect:**
A. While a bruise does appear after an injury, it is not true that it appears immediately. The latency period is due to the time required for blood leakage and accumulation beneath the skin.
B. The colour change of a bruise is not solely determined by the presence of blood. It is primarily due to the degradation of blood breakdown products, which alters the colour based on the stage of hemoglobin breakdown.
C. Although blood is present in the area during the initial stages, the colour change is primarily due to the degradation of blood products, not the presence of blood itself.

**Clinical Pearl:**
Understanding the colour changes of a bruise can be useful in assessing the severity of tissue damage and the stage of healing. These changes can help differentiate between a superficial contusion and a deeper laceration, for example. Additionally, the colour changes can indicate the need for further evaluation or management, such as in cases of delayed resolution or excessive discoloration.