Question

C‐reactive protein (CRP) is a protein found in blood plasma that is a marker of inflammation. In healthy patients, its concentration is less than 0.000976 %wt in blood plasma. However, in patients with a bacterial infection, CRP levels are typically 0.0039 – 0.0195 %wt in blood plasma.

To detect CRP, a BCA assay was performed (similar to the one you did in lab), in which a given volume of protein solution was mixed with 1.000 mL of the BCA working reagent, the mixture was heated at 37 °C for 30 minutes, and the resulting purple solution’s absorbance was measured at 562 nm in a 1.000 cm pathlength cuvette.

When 100 L of a 501 ppm CRP solution were analyzed by the above procedure, the measured absorbance was 0.888.

A patient’s blood sample was analyzed in the following way: 1.000 mL of blood plasma was subjected to several types of chromatography to purify CRP from the other proteins and small molecules in blood and concentrate the contents to 145.0 L in a buffer solution. Then 100.0 L of the resulting solution were analyzed by the above procedure. The absorbance was found to be 0.604.

When 100 L of buffer were analyzed by the above procedure, the measured absorbance was 0.015. Assume all solutions (including blood) in this experiment have the same density.

Given the above information, determine the concentration of CRP in the patient’s blood plasma in units of %wt. Without performing any statistical tests, do you think the patient has a bacterial infection?

Answer 1

1) DETERMINATION OF ABSORPTIVITY FOR PURPLE SOLUTION INDICATOR OF THE PRESENCE OF CRP.

This interaction is described for Beer- Lamber Law:   

A= absorbance (adimentional) ; a: absorptivity (l/g.L); b=pathlength (cm) ; c: concentration (g/L)

A(562nm)=0,888

b= 1.000 cm

c=

then,    ========

Absorptivity is 1,77 L/g.cm

B) DETERMINATION OF CONCENTRATION OF CRP IN PATIENT`S BLOOD

A(solution CRP + buffer)= 0,604

A(buffer)=0,015

A(CRP)= 0,064-0,015=0,589

a=1,77L/g.cm

b=1cm

Using Beer-Lamber

in 100 mL CRP concentration is 0,033g = 0,033%wt in patients blood

THE PATIENT HAS A CRITICAL BACTERIAL INFECTION BECAUSE CRP CONCENTRATION IS MORE THAN 0,0195% wt