The Medical Laboratory’s role in Systemic Inflammatory Response Syndrome

In 1992, a new syndrome was introduced by the American College of Chest Physicians (ACCP) and the Society of Critical Care Medicine (SCCM), called Systemic Inflammatory Response Syndrome (SIRS). It is defined as 2 or more of the following variables:
- Temperature of more than 38° C or less than 36° C
- Heart rate of more than 90 beats per minute
- Respiratory rate of more than 20 breaths per minute or a PaCO2 level of less than 32 mm HG
- WBC count of >12,000/μL or < 4,000/μL or > 10% bands.
So what happens in SIRS?
Basically some insult occurs to the body which responds by having the basic inflammatory response. Part of that response is the release of cytokines that have the goal of returning the body back to a healthy state. However, if whatever caused the inflammatory response is not treated, or worsens, the amount of cytokines released cause destruction, not healing. This is known as a ‘cytokine storm’, resulting in hypotension leading to end organ dysfunction.
So what can the lab do to help diagnose SIRS?
Measuring cytokines such as Interleukin 6 would help, but this is not practical in most labs.
Being aware of the WBC count is the first step. As noted above, that is one of the criteria that has to be filled in the diagnosis of SIRS. While an elevated WBC is usually indicative of infection, the haematologist must also beware that other causes can cause an increase in the WBC count, such as leukemia and stress. A decrease in WBC isn’t usually associated with sepsis, but because infection can cause the increased transfer (or pooling) of neutrophils to the infection before the bone marrow can respond by releasing more into circulation.
Then there’s the subject of bands. Immature neutrophils, referred to as bands because that’s what the nuclear material in the cell looks like, a band. Under the eye of an experienced haematologist, bands can be identified when a manual differential is done.
Unfortunately, when it comes to the topic of band identification, sometimes it’s easier for theologians to discuss how many angels can stand on the head of a pin than it is for experience haematologist to agree to what a band cell is. Some labs avoid this minefield altogether by lumping in the neutrophil and band count together and leaving it up to a pathologist to comment if there are an increased number of bands present. Trivial point here, the term ‘shift to the left’, was used to indicate an increased number of bands present.
An arterial blood gas can be used to measure the PaCO2 level. If the level is <32 mmHG, that can be indicative of SIRS as well.
One of the cytokines released, Interleukin 6, will stimulate the release of C-Reactive Protein (CRP). An increase of CRP could also help diagnose SIRS.
A positive blood culture could also be a warning sign that SIRS is happening. Sepsis is one of the causes of SIRS.
Not the only cause though, and that is something the lab has to be aware of. Other causes of SIRS include ischemia, trauma or a combination of other insults, such as serious burns.
The important thing to remember is this, SIRS can become a serious threat to the well being of the patient. It is the laboratory’s job to be aware of it, and to help diagnose it.