13/10/2026
**ESR, CRP or Procalcitonin? A clinical guide to interpretation**
ESR, CRP and procalcitonin (PCT) are commonly used in clinical practice, but they answer different questions. Knowing when to order them—and how to interpret the result in context—is just as important as the value itself.
**ESR** changes relatively slowly and is influenced by factors such as age, anaemia, pregnancy and renal disease. It may be useful in selected chronic inflammatory conditions, but is less suited to assessing rapid changes.
**CRP** responds more quickly to inflammation and can help assess the clinical trajectory. However, infection is only one of many causes of an elevated CRP, and a low early result does not exclude an evolving infection.
**Procalcitonin (PCT)** can support antibiotic-stewardship decisions in selected patients. In adults with sepsis or septic shock, the 2026 Surviving Sepsis Campaign suggests using PCT alongside clinical evaluation to help guide antibiotic discontinuation when the optimal duration is unclear and source control is adequate. PCT should not replace clinical assessment when deciding whether to initiate antibiotics.
In practice, interpret all three markers alongside the history, examination, microbiology, timing of sampling and response to treatment. An isolated result rarely tells the whole story.
