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Common Blood and other Pathology Tests in the Intensive Care Unit


In order to identify actual or impending problems and to monitor the effects of treatment, critically ill patients will have a wide variety of pathology tests on different body fluids (E.g. blood and urine).

Why do intensive care patients have lots of blood tests?

Patients in intensive care are seriously ill and their condition changes often. In order to identify actual or impending problems and to monitor the effects of treatment, critically ill patients will have a wide variety of pathology tests on different body fluids (E.g. blood and urine).

Why so many different tests and so often?

The types of tests and how often these tests are performed depend on why the patient is in ICU and how stable the patient is. Most commonly, testing is on admission to the ICU and then on a daily basis. However, in a number of different circumstances, some tests will be repeated quite frequently.

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How are the tests done?

Most tests are done using the same techniques as an outpatient pathology service. However, because of the increased frequency of blood taking, an arterial line is often used to minimise patient discomfort from repeated needles. Unfortunately, some tests cannot be done using an arterial line. All staff taking blood tests are trained to minimise patient discomfort when performing these tasks. These pages will describe the common tests.

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Who will explain the results to me?

Under most circumstances the explanation given will be general, stating whether the results were normal or abnormal. It is probably not useful for you to become preoccupied with the day-to-day results of most blood tests. A proper understanding of the results is difficult without a background in medicine or the related sciences. However results that are of a critical concern will usually be related to you, examples could include a low Hb (known as anaemia) or worsening kidney function.

If you have further questions please ask the nurses and doctors caring for your loved one.

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Blood Tests

EUC – Electrolytes (Sodium/Potassium/Chloride)/Urea/Creatinine

This test involves taking between1-4 mls of blood from either a vein or an artery. This test looks at the basic chemical balance of the blood as well as kidney function. An imbalance in the chemical makeup of the blood will occur in a number of circumstances. This test will also indicate whether replacement of a body salt is required. Urea and creatinine are a direct measure of how well the kidneys are working.

This test is usually performed on admission to the ICU and on a daily basis. If there is a concern regarding the kidney function or chemical balance the EUC will be repeated more often. For example when a patient is on dialysis this test is usually done 4 times a day. If potassium (an essential body salt) is replaced the test may be repeated to see if enough has been given. An arterial line is often inserted because of the need to take a number of these tests.

The results are usually available in 1-2 hrs.

This is a picture of a patient having blood taken from a vein in the elbow. It was found using a google image search at this Website.

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Arterial Blood Gas - ABG

This test involves taking a small amount of blood, around 1-2 mls from an artery. This test is extremely important for several reasons.

  • Firstly, it tells the medical staff how well the lungs are functioning (indicates the oxygen and carbon dioxide levels).
  • Secondly, it will show whether or not the respiratory support the patient is receiving is sufficient.
  • Lastly it gives an indication of the acid-base balance in the body.

Examples of conditions where this is important could include pneumonia, poorly controlled diabetes, cardiac failure and renal failure.

This is a picture of a patient having an ABG taken from the radial artery. Picture found using google image search at this Website

Most patients in ICU will require at least one ABG, usually on admission. This test is done more frequently than EUC, especially if the lung function is impaired and/or the patient is receiving respiratory support (Eg BiPAP, ventilator or oxygen mask). An ABG is done using a smaller needle than other blood tests but blood must be takenfrom an artery. The most common arteries used are those in the patient’s wrists because these arteries are easily accessible. Some bruising may result after this test is done. An arterial line is often inserted because of the need to take a number of ABGs. The results are usually available in a short time.

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Liver Function Tests - LFTs

Blood to do this test is included in a sample taken for EUC. As the name suggests this test evaluates the function of the liver. The liver cleanses the blood of waste products and is quite susceptible to poor function in a number of critical conditions. The test is usually done daily with results available in 1-2 hours.

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Cardiac Enzymes - CE

There are a number of cardiac enzymes that are released into the blood when there is damage to the heart muscle. CPK and troponin are the two most commonly measured. C.Esare usually done several times in the first 24 hours if a cardiac incident is suspected. For patients admitted to the coronary care unit (CCU) CE are usually done on a regular basis.

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Full Blood Count - FBC

This blood test involves taking approximately 4 mls of blood from a vein or artery. As the name suggests this test ‘counts’ the number of each of the different blood cells in the blood.

Haemoglobin or ‘Hb’ is an indication of those parts of the blood cells, which carry oxygen around the body. A low Hb is called anaemia. A blood transfusion may be required if the Hb is considered to be too low. The white cell count (WCC) is an indication of infection or inflammation in the body. Platelets form an integral part of the clotting mechanism of the blood.

A FBC is usually done on admission and then daily. If blood transfusions are required or there is a concern regarding bleeding the FBC will be done more frequently.

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Coagulation Studies - Coags

This blood test evaluates the blood’s clotting status. Blood clotting is a complex process that can be affected by a number of critical illnesses. Regular coagulation studies are required when a patient is receiving anti-clotting drugs such as heparin or warfarin. The test requires around 4 mls of blood from a vein or artery. The test is done on admission and then daily unless the coagulation status is abnormal. When starting a heparin infusion or commencing warfarin therapy frequent testing may be required before the right dosage is established. This may mean a number of tests per day. If in place an arterial line can be used.

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Blood sugar level - BSL

A BSL can be done in different ways. The blood specimen may be obtained from a specimen used for a EUC or an ABG or using the finger prick method. The test is generally done at the patient’s bedside using a small glucometer. The BSL is becoming a more important blood test. Unless there is a concern over the level of sugar in the blood the BSL is usually done 1 to 2 times a day. The BSL will be done more frequently if the patient is diabetic, the BSL is unstable, the patient is receiving a medication that could affect the BSL or if keeping the BSL within a tight range is required.

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Other Tests


A urinalysis is a routine test performed by the nursing staff in intensive care. It involves taking a small amount of urine and inserting a test strip into it. This strip can indicate a number of abnormalities including infection, dehydration, abnormal kidney or liver function, presence of glucose or ketones or blood. There is no risk to the patient.

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Pathology Tests to identify possible infection

A septic workup involves taking a number of specimens from an intensive care patient in whom an active infection is suspected. This will normally involve blood cultures, a sputum and urine specimen as well as samples from any other sites such as wounds. A septic workup is usually done on patients with a high or increasing temperature or patients who have been in ICU for a lengthy period.

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Blood Cultures

Blood cultures are done when an infection is suspected and to monitor the progress of antibiotic treatment. Usually two sets of tests will be done initially, followed by further tests as required. Some units do routine surveillance blood cultures on long-term patients to idetify impending infections early.

This test involves taking 10-20 mls of blood from a vein under sterile conditions. This blood is placed into specific specimen bottles and sent to the laboratory. Here small amounts of blood are placed onto special plates to see what organisms may be growing in the blood. The test is done when the patient has the symptoms of an infection, such as a raised temperature, a low blood pressure or a wound that appears infected. Specimens for a blood culture must be taken from a sterile site so an arterial line is unsuitable.

A preliminary result will be available within several hours however the final results from a blood culture can take several days. If a patient is quite sick with a suspected infection antibiotics will be started before the full test results are available. This antibiotic regime may then be adjusted when the full results are available. Unfortunately, it is not always possible to identify the cause of the infection.

This is picture of typical blood culture bottles found through a google image search. Website

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MSU – mid stream urine test

A MSU involves obtaining a small volume of urine under as clean conditions as possible. Since most critically ill patients have a urinary catheter in place obtaining a clean specimen is quite easy. The urine specimen is taken to the microbiology laboratory and tested to identify an infection. The results are generally available in 1-2 days. If there is a suspicion that the renal (kidney) system is the source of a possible infection broad spectrum antibiotics will be started until the infective organism is identified.

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Sputum Specimen

The lungs are quite often the source of an infection in the intensive care patient. There is normally a number of organisms in the throat and upper airways of a person. The presence of organisms in the sputum of a patient does not necessarily mean that the patient has pneumonia. A sputum specimen can be obtained in a number of ways. Ideally the sputum should be from deep inside the lungs, so simply coughing the sputum into a specimen container is not always suitable. Usually the ventilated patient will simply be suctioned with a clean suction catheter. To obtain the optimal sample a bronchoscopy may need to be done. Alternatively a simpler technique called a non-bronchoscopic bronchi alveolar lavage (NB-BAL) may be used. In both of these techniques 20-40 mls of saline are injected into the lower airways and immediately suctioned out. This ‘washes’ out the lower airways and returns a cleaner sample for examination.

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Wound Swabs

If a wound, such as an abrasion or surgical incision, appears infected, a wound swab is usually done. This involves cleaning the wound with normal saline and ‘wiping’ a sterile swab across the wound. This swab looks much like a cotton wool bud with a longer handle. The swab is taken to the microbiology laboratory for testing. Results take several days. Occasionally a wound may be opened because there may be a large amount of swelling and/or discharge. Superficial wounds generally don’t require antibiotic treatment. If the wound is considered to be causing a generalised infection antibiotic treatment may be commenced.

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CSF – Cerebrospinal Fluid

This is the fluid that bathes the brain and spinal cord. A specimen of this fluid is obtained in different ways. Firstly a lumbar puncture may be performed. This procedure involves inserting a needle between two vertebrae in the lower back under sterile conditions. The needle goes into the subarachnoid space, and a small amount of CSF is drained and sent to the laboratory for the identification of infection and other abnormalities. A lumbar puncture may be performed in intensive care if there is a suspicion of an infection. Secondly if the patient has an intraventricular drain insitu, a CSF specimen will be sent for identification of possible infection as a routine procedure.

These pictures demonstrate the two common positions a patient may be in for a lumbar puncture. The ICU patient will generally be lying down. The picture was found using a google image search at the following Website.

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Other body fluids

Samples of fluids from other parts of the body may be sent for examination if they could be the source of infection. If the patient has a drain in place a sample from this site is easily obtained (E.g. intercostal catheter).

There is a very long list of blood and other tests, which are carried out on intensive care patients. However it is beyond the capacity of this site to list and describe them all. Please ask the medical and nursing staff caring for your loved one to explain any additional tests that have been done.

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Common Blood and other Pathology Tests in the Intensive Care Unit Version 1.2 (Author: K Rolls CNC ICCMU) First posted November 2005, revised July 2009

The information contained on this page is general in nature and therefore cannot reflect individual patient variation. In addition it reflects Australian intensive care practice which may differ from other countries. It is meant as a back up to specific information which will be discussed with you by the Doctors and Nurses caring for your loved one. ICCMU attests to the accuracy of the information contained here BUT takes no responsibility for how it may apply to an individual patient. Please refer to the full disclaimer.

Last Updated on Wednesday, 18 December 2013 23:47