**Core Concept**
Lead poisoning is a toxic condition caused by exposure to lead, which can occur through various routes, including inhalation, ingestion, or skin contact. The effects of lead poisoning can range from mild to severe and are influenced by the duration and intensity of exposure.

**Why the Correct Answer is Right**
The least common complication of lead poisoning in adults is **Abdominal X-ray abdominal calcification**. This is because lead poisoning primarily affects the nervous, hematological, gastrointestinal, and renal systems. While abdominal calcification can occur due to chronic lead exposure, it is relatively rare compared to other complications such as anemia, peripheral neuropathy, and encephalopathy.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Gastrointestinal symptoms** are common in lead poisoning, including abdominal pain, nausea, and vomiting. However, they are not the least common complication.
* **Option B:** **Neurological symptoms**, such as peripheral neuropathy and encephalopathy, are more common than abdominal calcification in lead poisoning.
* **Option C:** **Renal impairment** is a known complication of lead poisoning, but it is not the least common.

**Clinical Pearl / High-Yield Fact**
Chronic lead exposure can also cause anemia, which is often diagnosed through a complete blood count (CBC) showing microcytosis (small red blood cells) and basophilic stippling (inclusion bodies within red blood cells).

**Correct Answer: D. Abdominal X-ray abdominal calcification**