## Core Concept
The estimation of total serum protein is a crucial laboratory test that helps in assessing the nutritional status, liver function, and overall health of an individual. Various assays are employed for this purpose, each with its specific principle and application. The question requires identifying an assay not used for estimating total serum protein.

## Why the Correct Answer is Right
The Biuret test is a widely used method for estimating total serum protein. It is based on the reaction of peptides or proteins with copper(II) sulfate in an alkaline solution, resulting in a purple-colored complex. The intensity of the color is directly proportional to the protein concentration.

## Why Each Wrong Option is Incorrect
* **Option A:** The Kjeldahl method is indeed used for estimating total serum protein. It involves the digestion of proteins with sulfuric acid to convert them into ammonia, which is then estimated. This method is accurate but time-consuming and labor-intensive.
* **Option B:** Refractometry is another technique used for estimating total serum protein. It measures the refractive index of serum, which correlates with protein concentration. This method is quick and useful for a rapid assessment.
* **Option D:** The Dumas method, similar to the Kjeldahl method, is used for protein estimation. It involves the combustion of the sample and measurement of the nitrogen released.

## Why Option C is Incorrect (Correct Answer)
* **Option C:** The Bradford assay is primarily used for estimating protein concentration in solutions but is more specific to quantifying proteins in a purified form or in samples where the protein of interest needs to be quantified. It is not typically used for estimating **total serum protein** because it can be affected by the presence of various substances in serum.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while various methods can estimate total serum protein, each has its limitations and specific applications. For instance, the Biuret test is commonly used in clinical settings due to its simplicity and speed.

## Correct Answer: C. Bradford assay.