**Question:** In estimation of bilirubin, the solution is examined at

A. 410 nm
B. 540 nm
C. 550 nm
D. 630 nm

**Correct Answer:** D. 630 nm

**Core Concept:**
Bilirubin is a yellow-colored pigment produced as a result of the breakdown of heme in red blood cells. It is primarily responsible for the yellow color of the skin, sclera, and urine in jaundice. Bilirubin is measured in blood tests to assess liver function and hemolysis.

**Why the Correct Answer is Right:**
The correct answer, 630 nm, is chosen because it is the wavelength at which bilirubin exhibits its maximum absorbance in the ultraviolet-visible spectrum. Absorbance of light at this wavelength corresponds to the concentration of bilirubin in the sample. By comparing the absorbance of the sample to a standard curve of known bilirubin concentrations, the concentration of bilirubin in the test sample can be determined.

**Why Each Wrong Option is Incorrect:**

A. 410 nm: Bilirubin exhibits minimal absorbance at this wavelength, making it unsuitable for measuring bilirubin concentrations.
B. 540 nm: Bilirubin has a moderate absorbance at this wavelength, but 630 nm provides a more accurate measurement due to higher absorbance.
C. 550 nm: Bilirubin has a peak absorbance at 540 nm, but 630 nm provides a more accurate measurement due to higher absorbance.

**Clinical Pearl:**
The use of the correct wavelength ensures accurate estimation of bilirubin levels in patient samples, which is crucial for diagnosing and monitoring conditions like hyperbilirubinemia, Gilbert's syndrome, and neonatal jaundice. Misreading bilirubin levels can lead to misdiagnosis and suboptimal management of these conditions. Understanding the relationship between wavelength and bilirubin absorbance is essential for medical professionals to provide accurate medical care.