High-sensitivity CRP (hs-CRP) measures very low concentrations of C-reactive protein in the blood using a more sensitive assay than standard CRP testing. While standard CRP detects moderate-to-large elevations from acute illness or infection (above 5 mg/L), hs-CRP measures concentrations below 3 mg/L that are below the detection threshold of standard assays.

These low levels of chronic low-grade inflammation, previously considered clinically insignificant, are now recognised as independent predictors of cardiovascular disease risk. The Reynolds Risk Score and other cardiovascular risk calculators incorporate hs-CRP. People with hs-CRP persistently above 3 mg/L have significantly elevated cardiovascular risk, even when standard lipid panels appear normal.