Testing for Sepsis

Unlike diseases or conditions like diabetes or kidney stones, there is no one test that can tell if you have sepsis. Diagnosis is made after your doctor evaluates your symptoms, your history, and other tests that may indicate you have an infection. This can then lead your doctor to suspect you have sepsis.

Here are some of the tests that may be done to help determine if you do have sepsis.

Blood tests

Blood test results show healthcare providers many things about your body, from the possibility of an infection to how well your body’s organs are working. These are some of the more common blood tests that may be done when a patient presents with possible signs and symptoms of sepsis. None of these tests can diagnose sepsis, but when the test results are combined with information about your illness and a physical examination, they can help your doctor determine if you have sepsis:

Complete blood count (CBC): A CBC is a common blood test. It measures how many white blood cells are circulating in your blood, among other things. White blood cells (also called leukocytes) fight bacteria, viruses, and other organisms your body identifies as a danger. A higher than normal amount of WBCs in your blood could mean that you have an infection. Too few WBCs can indicate that you’re at risk of developing an infection.

Lacate: Your organs may produce lactic acid when they are not receiving enough oxygen. This can be caused by intense exercise, heart failure, or serious infection, among other conditions. A high level of lactic acid caused by infection can be an important clue that you have sepsis.

C-reactive protein (CRP): C-reactive protein is produced by your body when there is inflammation. The inflammation can be caused by several conditions, including infections.

Blood culture: A blood culture test is done to try to identify what type of bacteria or fungi has caused an infection in the blood. Blood cultures are collected separately from other blood tests and often they are taken more than once from different veins. It can take several days to get the results of a blood culture.

Prothrombin time and partial thromboplastin time (PT and PTT), platelet count, and d-dimer: Sepsis can have serious affects on the blood clotting in your body. If the PT and PTT are too high it can indicate that your blood is not clotting well. Platelets are tiny cells in your blood that help to form blood clots. If your platelet count is too low, it can mean that your body is forming many unseen clots in tiny vessels all over your body, and this can be an important sign of sepsis. The d-dimer test also indicates that blood clotting is happening in your body. The level of d-dimer can be high if you have one large clot, or it can be high if your body is making many tiny clots, as happens in sepsis.

Confirmatory Tests

The following three tests are what doctors call confirmatory tests. The test results give the medical team more information when they suspect sepsis. Patients and their doctors need to first recognize the clinical signs and symptoms for the tests to be ordered, however. If your doctor suspects sepsis, treatment (with fluids and antibiotics) should begin right away, while waiting for these confirmatory test results.

Endotoxin is a component of certain bacteria and is released when the bacteria cell disintegrates. It should not be in your blood, so its presence confirms that there are gram negative bacteria in your bloodstream, although this test cannot identify which type. This test is not a replacement for blood cultures.

Procalcitonin (PCT): Procalcitonin is a protein in your blood that rises if you have a bacterial infection. It cannot tell what type of bacterial infection you may have. If you have low levels of PCT, your doctor may rule out that your illness is caused by a bacterial infection and may be caused by a viral infection or an illness not related to an infection.


Urine tests

Urinalysis: Like the CBC, this simple urine test can tell your doctor a lot about your health, including if you have a urinary tract infection (UTI) or problems with your kidneys, such as a kidney stones. There is no special preparation to provide a urine sample for a urinalysis.

Urine culture: A urine culture is performed to determine what bacteria or fungi has caused a UTI. Urine for a culture must be obtained midstream. You will be given a special cleanser to wipe your genitals before you start urinating. Once you have cleaned the area as instructed, urinate for a few seconds into the toilet and then place the container under the flow and collect the sample.

Tests for specific infections

In addition to blood and urine tests, your doctor may want you to undergo other tests to identify where the infection may be. Here are some examples:


Chest x-ray: A chest x-ray will show if you have pneumonia or if there is damage around the lungs. A chest x-ray can’t tell your doctor what type of infection you have.

Pulse oximetry. A pulse oximeter measures the oxygen saturation level of your blood. This tells your doctor how well your lungs are taking oxygen from the air and putting it into your bloodstream. This simple test is done by placing a clip on your finger or ear lobe. The clip uses a light to measure the oxygen levels as your blood flows past.

Sputum test. If necessary, your doctor may ask for a sputum (phlegm) sample to be cultured.


Computerized tomography (CT) scan: A CT scan of your head may show if there is any swelling or inflammation caused by meningitis.

Magnetic resonance imaging (MRI): An MRI of your head may be done instead of a CT scan, to check for swelling or inflammation.

Lumbar puncture: Also called a spinal tap, a lumbar puncture allows your doctor to obtain a sample of cerebral spinal fluid (CSF), fluid that circulates around your spine and brain. Your doctor inserts a needle into your spinal cord, in your lower back, to remove a small amount of fluid to send for testing.

Strep throat

There are two tests for strep throat, the rapid antigen test and the throat culture. For the rapid antigen test, your doctor or nurse uses a swab to get a sample from the back of your throat. This test takes only minutes to show if there is bacteria that causes strep throat. A throat culture is done the same way, but using a special swab that is sent to a lab to be tested, similar to a blood culture or urine culture.


Influenza, the flu, is usually diagnosed by your symptoms. There are tests called rapid influenza diagnostic tests that may indicate what type of influenza you have, but they are not always accurate. To perform this test, a sample is taken with a swab swiped inside your nose or the back of your throat.

Skin infections

If your doctor suspects you have an infection on your skin, such as cellulitis or MRSA, a culture is needed to determine what type of infection you may have. This is done by injecting a small amount of saline solution under your skin, then withdrawing it and sending it for culture.

The symptoms of early sepsis are vague and may be easily dismissed. If you have had any invasive procedures (such as a surgery), had an invasive device inserted (such as an IV), or any type of break in your skin (such as a bug bite or cut), and you experience any of the symptoms, be sure to mention this to your healthcare provider.