A new turbidimetric method for assaying serum C-reactive protein based on phosphocholine interaction.
BACKGROUND
C-reactive protein (CRP) is able to bind phospholipids (mainly phosphocholine) in the presence of calcium ions. We investigated the use of this property for developing an affordable turbidimetrical CRP assay based on diluted soy oil.


METHODS
Serum (or heparinized plasma) was mixed with Intralipid 20% in Tris-calcium buffer (pH 7.5). After 30 min of incubation at 37 degrees C, the CRP-phospholipids complexes were measured by turbidimetry (660 nm/700 nm) with a Cobas 6000 analyzer (Roche). Results were compared with those obtained using a typical immunoturbidimetric method (Roche).


RESULTS
Good correlation (r(2)=0.931) was obtained between the functional and the immunoturbidimetric CRP assay. Within-run and between-run %CV values for the functional assay were 2.4% (100 mg/L); 6.0% (50 mg/L); 10% (20 mg/L), and 3.6% (100 mg/L); 8.0% (50 mg/L); 11% (20 mg/L), respectively. The limit of detection was 7 mg/L. Results were not affected by serum calcium, triglyceride, or phospholipid concentrations.


CONCLUSIONS
The functional CRP assay allowed measurement of CRP in serum and plasma in the range of 7 mg/L-400 mg/L. The assay is particularly suited in conditions where resources are restricted. Since the assay is species independent, the described functional CRP assay could be used for veterinary purposes as well.
Department of Clinical Chemistry, Ghent University Hospital, Ghent, Belgium.
Pierrot L
PL
Tugirimana
Astrid L
AL
Holderbeke
Jos A
JA
Kint
Joris R
JR
Delanghe
D001665:Binding Sites; D002097:C-Reactive Protein / Q000032:analysis* / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D005434:Flow Cytometry; D006801:Humans; D007477:Ions / Q000737:chemistry; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D010743:Phospholipids / Q000032:analysis* / Q000737:chemistry*; D012680:Sensitivity and Specificity
D007477:Ions; D010743:Phospholipids; D002097:C-Reactive Protein; D002118:Calcium