It can be confusing can’t it? Where do we start trying to work out what these different blood results mean to us as patients? This is not a comprehensive analysis of each test but should give you some background as to the reason why the ESR, CRP and/or PV tests are done. Of course, in the overall assessment other blood markers may be equally important in assessing health such as WBC (white blood cell count), HB (haemaglobin), Neutrophils (gobble up the bugs so if you haven’t got any neutrophils you are not in a good place!) etc. but in this blog I have set out to discuss only the inflammatory markers.
ESR (Erythrocyte Sedimentation Rate), CRP (C-reactive protein) and PV (Plasma Viscosity) are all markers of inflammation.
The ESR is the rate at which red blood cells sediment in a period of 1 hour. To perform the test, anti-coagulated blood is placed in an upright tube and the rate at which the red blood cells fall is measured and reported in mm/h. When an inflammatory process is present, the high proportion of fibrinogen in the blood causes red blood cells to stick to each other and settle, thereby increasing the ESR level.
Generally, ESR does not change as rapidly as does CRP, either at the start of inflammation or as it goes away. Both tests are elevated in the presence of inflammation; however, CRP appears and then disappears sooner than changes in the ESR. However, because ESR is an easily performed test, many doctors still use it as a long term monitoring test to assess the amount of inflammation caused by RA.
The ESR is an easy, inexpensive, nonspecific test that has been used for many years to help monitor conditions associated with acute and chronic inflammation, including autoimmune diseases such as RA. ESR is said to be nonspecific because increased results do not tell the doctor exactly where the inflammation is in the body or what is causing it, and also because it can be affected by other conditions besides inflammation. Used on its own the ESR is not a reliable marker of active RA disease and the results must be used alongside the doctor's other clinical findings, the patient's health history, and results from other appropriate laboratory tests.
A rising ESR may mean an increase in inflammation and/or a poor response to a therapy; a decreasing ESR may mean a good response. Levels of ESR regarded as within normal range are between 1-7mm/hour. However, this increases with age and females tend to have a higher basal ESR anyway with menstruation and pregnancy sometimes causes temporary elevations.
C-reactive protein (CRP) is a protein found in the blood, the levels of which rise in response to inflammation. Measuring and charting CRP values can prove useful in determining disease progress and/or the effectiveness of treatments.
While the CRP test is not specific enough to diagnose a particular disease, it does serve as a general marker for inflammation in RA. It is ordered as a regular monitoring device and repeated to determine whether treatment is effective. This is particularly useful for inflammation problems since CRP levels drop as inflammation subsides and rise as inflammation increases. CRP levels can be elevated in the later stages of pregnancy as well as with use of birth control pills or hormone replacement therapy (i.e. oestrogen). Higher levels of CRP have also been observed in the obese. The ‘normal’ values for CRP are <6mg/L.
PV is technically a more challenging test, and not offered by many NHS laboratories which tend to go with either ESR or CRP. Plasma viscosity is used to monitor inflammation and treatment efficacy in the same way as the ESR/CRP and whilst it is regarded by some as a more superior test it doesn't seem to be considered any more reliable than the ESR because levels can be slow to change. It is however more sensitive and more specific than either ESR or CRP when monitoring the activity of RA. Smokers have slightly higher PV than non-smokers. Normal values at 37degrees are 1.05-1.30, High 1.3-1.6 (usually found in active RA), 1.47 and above synonymous with other conditions.
This is intended as general information only and not specific to any given person. My ESR is ‘acceptable’ when it’s between15-20mm/hr. Others may have a ‘normal’ reading that equates to ‘5’ or even ‘40’. We are all very different. It is important that blood results are not taken out of context but used with symptoms and a person’s well being to assess the overall picture. A ‘one off’ high or low blood result can be a rogue, don’t get yourself into a pickle if this happens, have the test repeated a few weeks later. Interestingly, I have had an ESR of 122 and a CRP of 1 at the same test … make of that what you will, the rest of us were very puzzled