Hey there, 

I hope you all had a lovely week. I had a very busy week that included family gatherings, an eight hour track meet, and, of course, my internship. But I can’t complain, I enjoyed each event, and I got to spend a lot of time with my baby cousin, who is almost 11 months old.

At my internship, I continued to look through patient charts and collect data. I have noticed things like nearly every single patient with a TKA infection has hypertension (high blood pressure). I have done some research on hypertension, and found that 64% of men, aged from 65-74, are hypertensive and 69.3% of women, aged 65-74, are hypertensive. Also, 66.7% of men ,aged 75 and older, are hypertensive and 78.5% of women ,aged 75 and older, are hypertensive (http://www.cdc.gov/bloodpressure/facts.htm). So far, 84% of the patients with a TKA infection are hypertensive. Using this information, doctors can inform patients with hypertension before the surgery, that they have a slightly higher risk of getting an infection. In the future, as I collect more data, I will distinguish which percent of men versus women have hypertension. 

I have also noticed a high amount of patients who have diabetes. According to American Diabetes Association, 25.9% of Americans aged 65 and older have diabetes, while 41% of the patients with a TKA infection have diabetes. This shows that people with diabetes have a higher risk of infection.

One thing I wish I had access to was patients who had a total knee arthroplasty surgery, but never got an infection. This way I could collect data and see what percent of patients did have hypertension and/or diabetes, but never got infected. But, unfortunately, this is not an option for me, and it will remain one of the flaws of my project. 

In the following weeks I will be sharing more data with you guys! See you then!

Komal Majhail

Hello again,

On last weeks post I talked about three laboratory tests: a white blood cell count, a c-reactive protein (CRP) count, and a erythrocyte sedimentation rate (ESR). As I said in the last post, I have found that these three test are usually the first tests to be ordered when their is suspicion of an infection. But if the results are elevated, doctors can not conclude a patient has an infection quite yet, they must proceed with laboratory tests that tend to be a little more invasive, such as a knee aspiration (aka arthrocentesis). You might be wondering, whats the point of the first three tests if you can’t even use them for diagnosing an infection. Well the point is to confirm a doctors suspicion that the knee is not doing well with the prosthesis, and that much more invasive clinical procedures and laboratory tests need to be performed. 

A knee aspiration is the clinical procedure of using a syringe to draw fluid from the knee. As you can imagine this is much more painful than getting your blood drawn (a blood sample is all that is needed for the CRP, ESR, and WBC count tests). I will go more in detail about knee aspirations and how they pertain to TKA infections after mentioning some trends I have noticed. 

I have seen that a knee aspiration is usually the next step after the CRP, ESR, and WBC count tests. But, sometimes the knee aspiration is the first step, and this could be because the infection is a bit more obvious in that patient, or because the laboratory test results were never imported into the patients chart (missing information is one of the flaws of this project). 

Anyways, the fluid from knee aspirations are sent to a laboratory where the fluid sample is placed in a dish and watched to see if bacteria, fungi, or viruses grow. If these germs are detected, than there is a strong chance of an infection. 

In an earlier post, I mentioned a certain set of criteria many doctors follow when diagnosing an infection. I will include it in this post too, so you don’t have to go back. 

1) There is a sinus tract communicating with the prosthesis; or
2) A pathogen is isolated by culture from at least two separate tissue or fluid samples obtained from the affected prosthetic joint; or
3) Four of the following six criteria exist:

a) Elevated serum erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) concentration,

b) Elevated synovial leukocyte count,

c) Elevated synovial neutrophil percentage (PMN%),

d) Presence of purulence in the affected joint,

e) Isolation of a microorganism in one culture of periprosthetic tissue or fluid, or

f) Greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification.

Number 2 and letter e are both talking about knee aspirations. If a pathogen is isolated it means that something grew in the dish and there is a strong chance of infection. Based on this set of criteria, if a pathogen is isolated from two separate fluid samples, than it is safe to say the patient has an infection. But if only a single fluid sample grows a germ, than three other criteria must be met to diagnose a patient with a TKA infection. 

I’m going to stop here, but In next weeks blog I will go over the last few laboratory tests that are used in diagnosing a TKA infection. 

See you then, Komal.

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