Prognostic utility of biochemical markers of cardiovascular risk: impact of biological variability.

BACKGROUND

Although a variety of biochemical markers are used to help predict the risk of cardiovascular disease, the prognostic utility of any marker used as a risk assessment tool is dependent on the long- and short-term biological variability that the marker shows in different individuals.

METHODS

We measured total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol; triglycerides; high-sensitivity C-reactive protein (hsCRP); total fibrinogen; and γ' fibrinogen in blood samples collected from 15 apparently healthy individuals over the course of 1 year. Repeated measures variation estimates were used to calculate short- and long-term intraclass correlation coefficients (ICC), within- and between-subject coefficients of variation (CVI and CVG, respectively), validity coefficients, and indices of individuality for each marker.

RESULTS

HDL cholesterol demonstrated the lowest variability profile, with an ICC of 0.84 and CVI of 11.1 (95% CI: 8.3, 17.0). hsCRP showed the highest levels of short- and long-term within-subject variability [CVI (95% CI): 54.8 (32.8, 196.3) and 77.1 (53.3, 141.3), respectively]. Stated differently, it would require five separate measurements of hsCRP, performed on samples collected over multiple days, to provide the risk assessment information provided by a single measurement of HDL cholesterol. γ' Fibrinogen demonstrated an ICC of 0.79 and CVI of 14.3 (95% CI: 10.6, 21.9).

CONCLUSIONS

hsCRP showed very high biological variability, such that a single measurement of hsCRP lacks sufficient clinical utility to justify routine measurement. The variability profile of γ' fibrinogen was not markedly different than HDL cholesterol, necessitating only a limited number of measurements to establish an individual's risk of cardiovascular disease.