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Abstract
Background:
Recently developed full-range C-reactive protein (CRP) tests, which are based on the immunoturbidimetric method, have wider analytical measurement ranges (AMR) than previously used tests. We evaluated the AMR of 3 full-range CRP tests-2 new and 1 previously used test.
Methods:
We analyzed the precision and AMR of 2 full-range CRP tests (Sekisui, Nanopia CRP, N-CRP and Iatron, IATRO CRP-EX, I-CRP) and compared the values obtained for these tests with those obtained for the conventional full-range CRP test (Sekisui, PureAuto S CRP, P-CRP). We evaluated the tests for the limit of quantification and for linearity. We also compared these results of these tests by using the comparative test (Dade Behring, cCRP) for cardiovascular risk assessment.
Results:
Coefficients of variation (CVs) of all the full-range CRP tests were less than 10% for concentrations greater than 0.6 mg/L, and CVs of N-CRP and I-CRP were lower than those of P-CRP for concentrations less than 1 mg/L. N-CRP (0.1-467 mg/L) and I-CRP (0.1-280 mg/L) had wider AMR than P-CRP (3-233 mg/L). All the full-range CRP tests showed more than 90% agreement with the cCRP values for the assessment of cardiovascular risk.
Conclusions:
The 3 full-range CRP tests, by virtue of their wide AMR, may be used for the detection of acute inflammation as well as for the assessment of cardiovascular risk. N-CRP and I-CRP may be more useful than P-CRP for determining the CRP concentration, especially for the detection of concentrations close to the lower or upper limit of the analytical range, without the need for repetition of the test.
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Fig. 1.
Linearity of the 3 full-range CRP tests. The closed shapes are excluded from the linearity calculations and the open shapes (N-CRP, 10%-100%; I-CRP, 10%-60%; P-CRP, 10%-50%) indicate statistically linear range (P<0.05) with 2.5% of allowable nonlinearity.
Abbreviations: CRP, C-reactive protein; cCRP, cardiophase CRP; N-CRP, Nanopia CRP; I-CRP, IATRO CRP-EX; P-CRP, PureAuto S CRP.
Fig. 2.
Method comparison between cCRP and each of the 3 full-range CRP tests in 91 patient samples (0.2-8.0 mg/L) for cardiovascular risk assessment. (A) Linear regression analysis. The blue solid lines indicate the regression line, and the dashed lines indicate identity. S, I and the numbers in parenthesis indicate slope, intercept, and 95% confidence intervals (CI). (B) Bland-Altman analysis. The blue solid lines indicate the mean (m) of the difference, and the dashed lines (numbers in parenthesis) indicate 95% CI for the differences.
Abbreviations: See Fig. 1.
Fig. 3.
Method comparison among the 3 full-range CRP tests in 51 patient samples (10-300 mg/L). (A) Linear regression analysis. The blue solid lines indicate the regression line, and the dashed lines indicate identity. S, I and the numbers in parenthesis indicate slope, intercept, and 95% Confidence intervals (CI). (B) Bland-Altman analysis. The blue solid lines indicate mean (m) of the difference, and the dashed lines (numbers in parenthesis) indicate 95% CI for the differences.
Abbreviations: See Fig. 1.
Table 1.
Imprecisions of the cCRP test and 3 full-range CRP tests
| Pool | Full range | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| cCRP | N-CRP | I-CRP | P-CRP | ||||||
| Mean∗ (mg/L) | CV%† | Mean (mg/L) | CV% | Mean (mg/L) | CV% | Mean (mg/L) | CV% | ||
| 1 | (N=20) | 0.19 | 8.7 (8.7) | 0.24 | 9.1 (9.0) | 0.16 | 19.2 (18.0) | 0.15 | 35.0 (33.2) |
| 2 | (N=20) | 0.26 | 9.0 (8.8) | 0.42 | 8.9 (8.8) | 0.25 | 10.4 (10.4) | 0.24 | 17.2 (16.1) |
| 3 | (N=40) | 0.36 | 5.0 (4.8) | 0.48 | 5.5 (5.0) | 0.33 | 7.4 (7.1) | 0.35 | 13.8 (12.1) |
| 4 | (N=40) | 0.52 | 4.8 (3.5) | 0.56 | 5.1 (4.9) | 0.39 | 8.0 (6.5) | 0.47 | 15.0 (14.5) |
| 5 | (N=40) | 0.58 | 4.5 (4.0) | 0.70 | 4.2 (4.2) | 0.49 | 5.0 (4.7) | 0.56 | 9.7 (9.0) |
| 6 | (N=20) | 0.86 | 4.0 (4.0) | 1.12 | 3.2 (3.0) | 0.72 | 3.5 (2.9) | 0.82 | 5.0 (4.8) |
| 7 | (N=20) | 2.46 | 4.3 (3.9) | 2.49 | 1.8 (1.0) | 2.21 | 1.7 (1.5) | 2.47 | 1.7 (1.5) |
| 8 | (N=20) | 17.20 | 5.2 (3.5) | 17.00 | 1.5 (0.9) | 17.50 | 2.1 (1.8) | 17.60 | 1.1 (0.9) |
| 9 | (N=20) | 119.67 | 5.5 (5.0) | 129.16 | 1.0 (1.0) | 130.58 | 1.7 (1.6) | 160.59 | 2.0 (1.8) |
| 10 | (N=20) | NT | NT | 430.00 | 2.0 (2.0) | NT | NT | NT | NT |
Table 2.
Agreement of relative cardiovascular risk categories by cCRP test and 3 full-range CRP tests
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