CRP and ESR are two of the most commonly ordered blood tests, and both measure the same broad thing: inflammation somewhere in the body. They're useful clues, but they're also easily over-interpreted — a raised result tells you something is going on, not what. Here's how to read them sensibly.
What inflammation markers do
When there's inflammation — from an infection, an injury, or an inflammatory condition — the body produces certain substances that these tests pick up. They act like a smoke alarm: excellent at telling you there may be a fire, useless at telling you where it is or how big.
CRP, explained
CRP (C-reactive protein) is made by the liver and rises quickly — within hours — when inflammation appears, then falls quickly once it settles. That speed makes it handy for tracking something active, like whether an infection is responding to treatment. A high CRP suggests significant inflammation; a normal CRP makes a major active inflammatory process less likely.
ESR, explained
ESR (erythrocyte sedimentation rate) measures how fast red blood cells settle in a tube — they settle faster when inflammation-related proteins are present. ESR rises and falls more slowly than CRP, so it reflects a longer time window. It's also influenced by age, sex, anaemia and pregnancy, which is why it's always read in context.
Lots of things raise them
Because these markers are non-specific, many ordinary things push them up — a recent cold, a minor injury, a dental infection. That's why doctors don't diagnose from them alone. Instead, they use them to gauge how much inflammation is present and to follow whether it's improving or worsening over time.
What a result does and doesn't mean
A raised CRP or ESR is a reason to look further, guided by your symptoms — not a diagnosis in itself. A normal result is reassuring but doesn't completely rule out every problem. As with most lab values, the trend across several tests is far more meaningful than a single number, so keep your results together and review them with your doctor.