Infection, Septicaemia, Septic Shock and Sepsis

What is the difference?


An infection is when viruses, bacteria, fungi, parasites, or other microbes enter the body, start to multiply and then they start to damage the body’s cells.  Signs and symptoms of the infection appear as an illness and we feel unwell.

In response to an infection, our body’s immune system springs into action and normally releases chemicals into the bloodstream to fight the infection.


Septicaemia is a serious bloodstream infection.  Septicemia is caused by an infection in another part of your body.  It occurs when an infection spreads via the bloodstream from elsewhere in the body, such as the skin, lungs, kidneys or bladder.  This is dangerous because the infecting organism and their toxins can be carried through the bloodstream to your entire body.  Septicaemia can quickly become life threatening.  If left untreated, septicaemia can progress to sepsis or septic shock.


Sepsis is the body’s extreme response to an infection.  Sepsis occurs when your body has a strong immune response to the infection.  Sepsis is not an infection but a condition caused by the body’s response to an infection.  This leads to widespread inflammation throughout the body.  This inflammation causes blood clots and block oxygen from reaching vital organs, resulting in organ failure.  It is a life-threatening medical emergency.  Without timely treatment, sepsis can rapidly lead to tissue damage, organ failure, and death.

When this widespread inflammation occurs with extremely low blood pressure, it’s called septic shock.  Septic shock is fatal in many cases.

The role of a CRP (C-Reactive Protein) test

A c-reactive protein (CRP) test measures the level of c-reactive protein (CRP) in a sample of your blood.  CRP is a protein made by the liver.  Normally, you have low levels of c-reactive protein in your blood.  Your liver releases more CRP into your bloodstream if you have inflammation in your body.  High levels of CRP mean you have a health condition that causes inflammation.

A CRP test may be used to help find or monitor inflammation in acute or chronic conditions, including:

  • Infections.
  • Inflammatory bowel disease, disorders of the intestines that include Crohn’s disease and ulcerative colitis.
  • Autoimmune disorders, such as lupus, rheumatoid arthritis, and vasculitis.
  • Lung diseases, such as asthma.

The role of a Procalcitonin (PCT) test

A CRP test indicates inflammation.  It doesn’t provide proof of an infection or distinguish between bacterial or viral infections.

This is where a Procalcitonin (PCT) test is helpful.  A procalcitonin (PCT) test measures the level of procalcitonin in your blood.  Normally, you have very low levels of procalcitonin in your blood.  But if you have a serious bacterial infection, the cells in many parts of your body will release procalcitonin into your bloodstream.  A high level of procalcitonin in your blood may be a sign of a serious bacterial infection or sepsis.  PCT is a biomarker used to predict the likelihood of a patient having a bacterial infection and how severe that infection might be.

A procalcitonin test is mostly used if you are seriously ill and your provider thinks you may have a systemic infection (an infection that affects your entire body).  The test also helps find out whether bacteria or a virus is causing your infection.  For example, a procalcitonin test can help tell the difference between bacterial and viral pneumonia.  This matters because antibiotics may help bacterial infections, but not viral infections.

A PCT test helps to:

  • Diagnose or rule out a bacterial/viral infection.
  • Diagnose sepsis.
  • Find out how serious a sepsis may be.
  • Make treatment decisions.
  • Monitor how well treatment is working.
  • Manage antibiotic dosage and length of duration.
  • Provide useful treatment information leading to wise and informed decisions.