science Tuesday, September 7, 2010. Post by David Bradley
A while back my doctor did some routine tests for some vague symptoms I reported (all came back negative thankfully) and yes, I know you can get drugs to treat hypochondria.
Anyway, of those tests was an ESR (erthythrocyte sedimentation rate, also known as sed rate). A test for patients with wide-ranging symptoms that may be inflammatory in origin. From what I read when she ordered this test, it seems that it can provide a first pass test for arthritis, rheumatic problems, and even cancer. A negative result presumably rules out any disease state that’s at an advanced stage and so causing inflammation. But, I wondered how early the ESR could detect the first signs of arthritis, cancer etc, and couldn’t it be a generic screening test that everyone could have when they reach a certain age and every 5 or 10 years thereafter?
Having come up with this idea, I discovered a paper from some time back, that seems to suggest that the sed test could not be used as a general test for disease, but that paper is from 1999…
But, despite that paper, the sed test could spot the quite early stages of a disease then it could preclude the need for mammography, bowel screen, prostate testing etc. Maybe I’ve got ESR all wrong, but a quick blood test would be so much faster and cheaper than large, national screening programs.
I asked a physician friend about my idea. ESR is a test that we used to order a lot but we tend to use CRP (C-reactive protein) now, he told me. The ESR is a marker for acute phase proteins which reflect inflammatory processes. As I understand it the presence of more of these proteins affect the ability of red blood cells to form rouleaux – clumps of cells. So the rate at which red cells settle in a column is affected.
The ESR is a good marker for inflammation but not a diagnostic. Moreover, it goes up with age and anaemia. So I quite often may see a result of an ESR which is raised in an elderly person – if there is no previous result I am left thinking “Is this new or has it been up for a while?” CRP can be a useful adjunct, i.e. if the ESR is raised but the CRP normal then it is likely that the ESR is age related.
The CRP is one of the acute phase proteins so it tends to be more sensitive and go up and down more quickly. If I get a discharge summary from the hospital and the junior doctor has had time to write a bit then it is often the CRP that they quote (high when a patient went in and reducing on discharge).
As with ESR, CRP has many uses: screening for organic disease, monitoring disease activity in rheumatoid arthritis, infection or malignancy, as a marker for acute pancreatitis, to distinguish bacterial from viral infections.
ESR doesn’t fit the criteria for a screening test, but it is a screening tool. My contact adds that, “If I have a patient with vague symptoms returning to see me on a number of occasions then a blood screen that has a raised ESR (or CRP) is useful to alert me that there is something that needs pursuing. Conversely, most of the time, if it is “normal” then I will be partially reassured and keep monitoring the situation.”
So, it seems to be a useful tool, but I’d be interested in your qualified thoughts on whether it might be used as a universal screening tool for non-specific disease even in the absence of symptoms.
Brigden ML (1999). Clinical utility of the erythrocyte sedimentation rate. American family physician, 60 (5), 1443-50 PMID: 10524488
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