A crisis in a patient with sickle cell disease is most likely to be cause by
**Core Concept**
Sickle cell disease (SCD) is a genetic disorder characterized by the production of abnormal hemoglobin, leading to deformity of red blood cells (RBCs) under certain conditions. This abnormality causes RBCs to change shape, leading to vaso-occlusion and tissue ischemia.
**Why the Correct Answer is Right**
In a crisis, the sickled RBCs cause obstruction of blood flow in small vessels, leading to ischemia and pain. This is often triggered by dehydration, infection, or exposure to cold temperatures. The sickled cells are more prone to sticking together and adhering to the endothelium, further exacerbating the vaso-occlusive process.
**Why Each Wrong Option is Incorrect**
**Option A:** Infection is a common precipitating factor for sickle cell crisis, but it is not the primary cause. Infections can trigger a crisis by increasing the production of pro-inflammatory cytokines, which can further damage the endothelium and increase the stickiness of RBCs.
**Option B:** Dehydration is a known risk factor for sickle cell crisis, as it can increase the concentration of RBCs and reduce their deformability. However, it is not the primary cause of the crisis.
**Option C:** Cold temperatures can trigger a sickle cell crisis by causing the RBCs to sickle more easily. However, this is not the most common cause of a crisis.
**Clinical Pearl / High-Yield Fact**
Patients with sickle cell disease are more prone to infections due to functional asplenia, which results from the autosplenectomy caused by chronic vaso-occlusion in the spleen.
**Correct Answer:** D.