Nephritis - Rat Urinary Protein Assay

The rat urinary protein assay kit uses the turbidity method in a 96-well fl at bottom plate, which offers a solution for assaying a large number of rat urine samples within a short time. This kit requires a minimal volume (less than 10 μl) of urine sample, and is ideal for studying nephritis in various strains of rats that do not secrete a sufficient volume of urine during a 16-hour collection period.

Rat Urinary Protein Assay Kit and Standard

Turbidity Assay and Bradford Assay
The turbidity assay method has been widely used to determine urinary protein levels in human specimens, because it is accurate, easy to use, and economical. However, the current turbidity method requires large sample volumes, and cannot be used for assaying urine specimens from certain strains of rats, because of low urine volumes. Please note that the16-hour urine volume varies significantly from 0.1 to 20 ml depending on rat strains. Furthermore, reading turbidity (OD 450 nm) of individual test tubes using a spectrophotometer is time consuming. 

Protein concentrations in urine samples can be determined by Bradford assay methods.  However, the turbidity assay method using 3% sulfosalicyclic acid dihydrate is more convenient than the Bradford method because of the wider range (0.5 – 4.0 mg/ml) of the dose response curve (Figure 1). Importantly, regardless of which assay method is used, bovine serum albumin (BSA) cannot be used as a standard. The dose response curve of BSA significantly differs from the dose response curve of serum proteins in the turbidity assay. More importantly, the OD value of globulins by the Bradford assay method is only 70% of the value of BSA. Therefore, a standard protein solution prepared from normal rat serum is ideal for assaying urinary protein levels regardless of the assay method.

Figure 1 - Standard curve of rat urinary protein assay by the turbidity method in 96-well plate