Hey everyone,

This week I went through more patient charts, but I want to hold off sharing the trends that I have noticed until I gather a bit more information.

Since I have only mentioned the names of a few of the laboratory tests that are normally ordered when there is suspicion of infection, this week I decided that I would introduce the first three tests that are usually preformed in more detail.

The first two tests I want to talk about is the Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) tests. These tests are usually the first ones doctors order when their is suspicion of infection. Both tests are different ways to measure for inflammation. This ESR test measures the rate at which red blood cells sediment in a period of one hour. This test is done by taking a sample of blood from a patient and putting it in a tube. Then the tube will be placed vertically and allowed to sit, untouched, for period of one hour. During this hour the red blood cells will sink to the bottom of the tube, and the plasma will rise. The more the red blood cells sink, the greater the inflammation.

As seen in the picture, there are five samples of blood from five different patients. The red blood cells in the third tube have settled to the bottom of the tube faster than the red blood cells in the other tubes. This indicates that the third tube has the highest level of inflammation.

The CRP test measures for inflammation by determining how much c-reactive protein is in the plasma of a patients blood. The level of c-reactive protein rises when there is inflammation throughout the body. These two tests are helpful indicators of infection, but the problem with these test is that it only indicates that their is inflammation somewhere in the body, it cannot pin-point the exact location of inflammation. So if a patient has a cut, which will cause inflammation, than an ESR and a CRP test could give a false positive result. These test are especially not useful for patients that have rheumatoid arthritis (RA), since RA causes inflammation, it will most likely give a false positive result.

Another blood test that is usually ordered with the ESR and CRP test is a white blood cell count. Since white blood cells fight infections, an abnormally large presence of white blood cells would be a strong indication of infection. But similarly to the ESR and CPR tests, if the patient has other reasons for a high white blood cell count, such as being sick, it could give a false positive result. 

While the ESR, CRP, and WBC tests have their issues, they are still often the first few tests a doctor will order. These laboratory tests are only part of the first step to diagnosing an infection. If these tests all come back elevated, doctors generally still do not diagnose a patient as having an infection, instead they order a few more laboratory tests. Since this post is starting to get a bit long, I will talk about the following steps to diagnosing an infection on the next blog post. 

See you then, Komal