**Question:** In a sepsis patient with Total Leucocyte Count (TLC) of 15,000, Neutrophil count is 40%, Eosinophil count is 7%, Band cells count is 15%, Metamyelocytes count is 5%, and Lymphocytes count is 35%. What is the Immature to Total Leucocyte Ratio (I:T ratio)?

**Core Concept:** The Immature to Total Leucocyte Ratio (I:T ratio) is a clinical parameter used to assess the degree of myeloid maturation in a sepsis patient. It is calculated by dividing the sum of immature cells (Band cells and Metamyelocytes) by the total leucocyte count.

**Why the Correct Answer is Right:** In this case, we need to calculate the I:T ratio by following these steps:

1. Add the percentages of Band cells and Metamyelocytes: (15% + 5%) = 20%.
2. Divide this sum (20%) by the total leucocyte count (15,000): 20% / 15,000 = 0.0133.

The I:T ratio is 0.0133.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because it does not consider the sum of immature cells (Band cells and Metamyelocytes) in the total leucocyte count.

B. This option is incorrect as it does not calculate the actual sum of immature cells (Band cells and Metamyelocytes) before dividing it by the total leucocyte count.

C. This option is incorrect because it only considers the neutrophil count (40%) without considering the immature cells (Band cells and Metamyelocytes).

D. This option is incorrect because it does not calculate the actual sum of immature cells (Band cells and Metamyelocytes) before dividing it by the total leucocyte count.

**Clinical Pearl:** The I:T ratio can help differentiate between bacterial and fungal infections in patients with neutropenia. In bacterial infections, the I:T ratio is typically higher, while in fungal infections, it is lower. A value above 0.1 suggests bacterial infection, while a value below 0.05 suggests a fungal infection. However, this ratio should be interpreted in conjunction with clinical findings and other laboratory parameters.