An unconscious 50 year old known case of diabetes mellitus is brought to the ER. His medical records show he is on warfarin for atrial fibrillation. Which of the following investigations will not be done in this patient for work up?
**Core Concept**
In the context of an unconscious patient with diabetes mellitus and a history of atrial fibrillation on warfarin, the primary concern is to rule out bleeding as a cause of altered mental status. Warfarin, a vitamin K antagonist, increases the risk of bleeding due to its anticoagulant effects.
**Why the Correct Answer is Right**
Given the patient's history of diabetes mellitus and warfarin use, the first step in the workup would be to investigate for bleeding as a cause of altered mental status. A non-contrast head CT would be the preferred imaging modality to quickly assess for intracranial hemorrhage (ICH) without the risk of contrast-induced nephropathy, which is a concern in patients with renal impairment, often seen in diabetic patients. Furthermore, a non-contrast head CT is more sensitive and specific for detecting acute hemorrhage compared to other imaging modalities.
**Why Each Wrong Option is Incorrect**
* **Option A:** Lumbar puncture (LP) would not be the first-line investigation in this patient due to the risk of precipitating or exacerbating a potential subarachnoid hemorrhage, which could lead to a fatal outcome.
* **Option B:** MRI might be useful in detecting other types of intracranial pathology, such as ischemic strokes or tumors, but it would not be the initial investigation of choice in a patient with a high suspicion of bleeding.
* **Option D:** CT angiography might be useful in detecting vascular abnormalities or aneurysms, but it would not be the initial investigation of choice in a patient with a high suspicion of bleeding.
**Clinical Pearl / High-Yield Fact**
In a patient with altered mental status and a history of anticoagulation, a non-contrast head CT is the preferred imaging modality for quickly assessing for intracranial hemorrhage.
**Correct Answer: A. Lumbar puncture would not be done in this patient for workup.**