The Erythrocyte Sedimentation Rate (ESR; Sed Rate) and C-Reactive Protein (CRP) are blood tests known as “inflammatory markers.” This means that they are elevated when there’s general inflammation occurring in the body, a definition which is very vague. It may be an acute infection, either mild (“the Flu”) or severe (septic shock), or a chronic infection (HIV, TB, etc.). The inflammation may be from an auto-immune disease like rheumatoid arthritis, lupus, Crohn’s etc., or even from a heart attack, or metastatic cancer.
In a certain sense, these tests don’t diagnose anything specific. One lecturer I heard said, “A high Sed Rate proves for sure the lab was open that day.” So why do we order them?
Say a patient has joint aches all over the body. A high ESR or CRP could suggest a disease like rheumatoid arthritis, leading us to pursue diagnostics. If it’s normal, it doesn’t rule out the illness, but makes it less likely. A patient with chronic diarrhea probably has Irritable Bowel Syndrome, but a high ESR or CRP would lead us to consider Inflammatory Bowel Disease, like Ulcerative Colitis or Crohn’s. We sometimes diagnose Fibromyalgia in people with muscle aches all over, but a high ESR would lead us to question that diagnosis. By the way, click the link if you’d like an explanation of the word “syndrome.”
The ESR is normally less than 20 or 30. It can rise a little with age. But an ESR of 100 is very unusual, & makes us wonder about diseases like Active TB, blood cancers (especially Multiple Myeloma), Temporal Arteritis, HIV, Endocarditis, and several other severe infections. Sorting those out depend on the symptoms the patient had in the first place, but still, an ESR that high raises our eyebrows.