**Question:** All are tests done on blood, except: TN 11

A. Coagulation Tests (e.g., PT, APTT, and INR)
B. Serum Biochemistry Tests (e.g., Glucose, Creatinine, and Urea)
C. Hematology Tests (e.g., Hb, RBC, and WBC count)
D. Microbiology Tests (e.g., Culture and Sensitivity, and Serology)

**Correct Answer:** D. Microbiology Tests (e.g., Culture and Sensitivity, and Serology)

**Core Concept:** Blood tests are a crucial tool for evaluating a patient's health status, diagnosing diseases, and monitoring treatment responses. These tests can be categorized into different types based on their purpose and sample source.

**Why the Correct Answer is Right:**

Blood tests can be broadly classified into four categories: Coagulation tests, Serum Biochemistry tests, Hematology tests, and Microbiology tests. The correct answer, Microbiology tests, is not performed on blood samples, but rather on blood cultures, which are used to identify and determine the antibiotic sensitivity of pathogenic microorganisms. Microbiology tests rely on observing bacterial growth and susceptibility patterns, typically on agar plates.

**Why Each Wrong Option is Incorrect:**

A. Coagulation tests (PT, APTT, and INR) assess blood coagulation factors and clotting mechanisms, evaluating the patient's risk of bleeding or thrombosis. These tests involve measuring coagulation times and ratios, not blood cultures.

B. Serum Biochemistry tests assess liver, kidney, and other organ functions, electrolyte balance, and glucose levels. These tests analyze blood serum, not blood cultures.

C. Hematology tests (Hb, RBC, WBC count) measure blood cell concentrations, size, and shapes, providing information on anemia, infection, and inflammation. These tests analyze blood samples, not blood cultures.

**Clinical Pearls:**

1. Coagulation tests and serum biochemistry tests are essential for evaluating a patient's overall hemostasis and organ functions.
2. Hematology tests are crucial for assessing blood cell abnormalities, infections, and inflammation.
3. Microbiology tests, as explained, are performed on blood cultures, not blood samples.

**Explanation of Option D (Microbiology Tests):**

Microbiology tests are performed on blood cultures, which are obtained by inoculating blood samples into culture media and incubating them to grow microorganisms and determine their antibiotic sensitivity. The results of microbiology tests aid in identifying pathogens causing infections and determining the most effective antibiotics for treatment. Since the question specifically mentions "not performed on blood," we can deduce that it is discussing blood cultures and not the other types of microbiology tests performed on various body fluids or tissue samples.