**Question:** Detected by stool examination except -

A. Blood
B. Bile
C. Viruses
D. Parasites

**Core Concept:** Stool examination is a diagnostic tool used to detect various substances or pathologies present in the stool sample. It helps in the diagnosis of gastrointestinal disorders, infections, and diseases.

**Why the Correct Answer is Right:**

The correct answer, **B. Bile**, is not detected by stool examination because bile is a digestive fluid produced in the liver and stored in the gallbladder. It is secreted into the small intestine to aid in the digestion and absorption of fats. Stool examination primarily focuses on detecting pathogens, parasites, blood, and substances originating from the gastrointestinal tract.

**Why Each Wrong Option is Incorrect:**

A. **Blood** can be detected in stool examination during gastrointestinal bleeding or colorectal cancer.
C. **Viruses** are generally not detected in stool examination, as they primarily infect cells via the gastrointestinal tract and are diagnosed through viral culture or PCR tests.

D. **Parasites** can be detected in stool examination through the examination of stool samples under a microscope or using various staining techniques.

**Clinical Pearl / High-Yield Fact:**

Stool examination is a crucial diagnostic tool in identifying gastrointestinal infections and diseases. It enables the detection of various substances, including blood, parasites, and specific proteins or antigens associated with pathogens. Knowledge of the correct methodologies, such as wet mount or concentration techniques, is essential for accurate stool examination.

**Correct Answer:** C. Viruses

**Explanation:** Viruses are not typically detected in stool examination, as they primarily infect cells via the gastrointestinal tract and are diagnosed through viral culture, antigen detection, or PCR tests. Stool examination focuses on analyzing substances originating from the gastrointestinal tract, such as blood, parasites, and proteins or antigens associated with pathogens.