Diagnosing sepsis can be difficult. The criteria for diagnosis include high or low body temperature, fast heart rate and respiratory rate, plus a probable or known infection.
There is no single test that can identify sepsis. Healthcare practitioners typically order a combination of tests to help diagnose sepsis, distinguish it from other conditions, detect the inflammation associated with sepsis, and to evaluate and monitor the function of the affected person's organs, blood oxygenation, and acid-base balance.
Some tests that may be done to detect sepsis and identify an infection include:
- Procalcitonin – may be used in conjunction with clinical evaluations and other tests to determine the risk that seriously ill patients will develop sepsis, or their risk of progressing to severe sepsis, septic shock and risk of dying. This test can help distinguish sepsis from other conditions that cause similar symptoms and can help guide treatment. The level of procalcitonin in the blood increases rapidly and significantly when a person has sepsis.
- Gram stains and cultures – these tests are done in conjunction with one another. Cultures grow the bacteria that may be in a sample taken from the site of suspected infection, so they can be precisely identified and their susceptibility to various antibiotics determined. Gram stains are used to detect the presence and identify the general type of bacteria. A Gram stain may be done relatively quickly but is not definitive—it provides only presumptive results.
- Blood culture – one type of culture used to detect bacteria in the blood and evaluate their susceptibility to antibiotics
- Urinalysis and urine culture – to identify whether the source of infection is a urinary tract infection
- Cerebrospinal fluid (CSF) analysis, including a culture – may sometimes be done if it is thought that the person has an infection of the central nervous system (meningitis or encephalitis).
- Sputum culture – to help diagnose bacterial pneumonia
- Cultures of other body fluids may be done as needed to detect the source and type of infection.
Some general, non-specific tests that may be done include:
- Complete blood count (CBC) – to evaluate red and white blood cells and platelets
- Lactate – increased levels can indicate organ dysfunction
- Blood gases – to evaluate oxygen in the blood and acid-base balance
- Comprehensive metabolic panel (CMP) – to monitor the health of organs, such as the kidneys and lungs, and monitor electrolyte balance and blood glucose level
- Prothrombin time (PT) and/or partial thromboplastin time (PTT) – these tests may be done along with other clotting tests to help evaluate the person's coagulation system—the process that the body uses to form blood clots and stop bleeding.
- C-reactive protein (CRP) – to detect inflammation in the body
These tests may be ordered to evaluate the health of organs, detect complications, and to help locate an infection:
- ECG – to evaluate heart rhythm or injury
- CT (computed tomography) scan
- MRI (magnetic resonance imaging)
For more on imaging studies, see the web site RadiologyInfo.org.