laboratory methods to aid in the detection of sepsis

8/12/2019 Laboratory Methods to Aid in the Detection of Sepsis

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Laboratory Methods to Aid in the Detection of Sepsis

Au tho r: Lynne Bro d eur, MA , MLS(ASCP)

Rev iew er: DeRho nd a C ra w ford, MT(ASCP)


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Course Instructions

Please proceed through the course by clicking on the blue arrows or text links. Use the table of contents to monitor your

progress. Your progress will be saved automatically as you proceed through the course, and you may later continue where you

left off even if you use a different computer. You may encounter prac tice questions within the c ourse, which are not graded or

recorded.


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Course Info

This course carries the following continuing education credits:

l P.A.C .E. Contac t Hours: 1.00 hour(s)

Course Number: 578-041-12

l Florida Board of C linica l Laboratory Science C E - General (Clinical Chemistry/UA/ Toxicology): 1.00 hour(s)


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Development and Progression of Sepsi

Sepsis Definition

Sepsis is an overreaction by the immune system to

infec tion (usually bacterial, but could be viral, fungal, or

parasitic). It is a systemic inflammatory response, which

can be life-threatening.

A weakened immune system, certain chronic disorders,

an artificial joint or heart valve, and certain heart valveabnormalities increase the risk for sepsis. Sepsis has been

reported to be the most common cause of death in the

nonc oronary intensive care unit. Note that it is sepsis (the

immune system's response) that is usually the cause of

death and not the infection. Therefore, it is crucial that

the recognition of sepsis be made as quickly as possible.

Delay in identifying sepsis limits the effec tiveness of

treatment.

Sepsis includes two or more of the following symptoms:

l A body temperature >38C (100.4F) or 90 beats/minutel Respiratory rate >20 breaths/minute

l An a lteration in the white blood cell (WBC) picture, such as a c ount >12.0 x 109/L or 10% immature neutrophils

However, these inflammatory responses may also occur in the absence of infec tion, a condition termed systemic inflammatory

response syndrome (SIRS). When the c ause of the systemic inflammatory response is infection, the c ondition is defined as sepsis.


Additional Criteria for Diagnosis of Sepsis

Blood c ultures are important for diagnosis of sepsis, but they take time to grow. This time can mean the difference between life

and death for a patient. Although sepsis cannot be definitively diagnosed until it is determined that there is a b lood or tissue

infection, the diagnosis may still be made if other criteria strongly suggests its presence. If the patient exhibits altered mental

status and/ or edema in addition to the SIRS criteria, or if one or more of the laboratory test results shown below are obtained

along with evidence from the clinica l assessment, the physician may choose to start antibiotic treatment before the results of

the cultures are available:

l Hyperglycemia in the absence of diabetes

l Elevated C -reactive protein (CRP)

l Elevated procalcitoninl Elevated lactic ac id (lac tate)


Severe Sepsis


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If sepsis progresses to severe sepsis, organs begin to shut down. Multiple organ (lung, liver, and kidney) dysfunction is possible,

which may result in death. Severe sepsis is charac terized by organ dysfunction, hypoperfusion, and/or hypotension.


Septic Shock

A patient progresses to septic shock from severe sepsis if the hypotension due to the systemic infec tion does not respond to

fluid resuscitation. Septic shock is life-threa tening with a mortality rate o f 40 - 60%.


Sepsis and Bacterial Toxins

Sepsis occurs when toxins produced by the bacteria cause cells in the body to release cytokines. Cytokines then produce

inflammation. Even though cytokines aid the immune system in fighting infec tion, they also can have detrimental side effects

that may include vasoconstriction (restriction of blood flow) a nd hypercoagulation in capillaries that supply blood to organs.

This in turn can lead to a series of severe complications such as:

l Continuous cycle of inflammation and coagulationl Weakening of the heart caused by the strain of increased pumping in an attempt to compensate for the decreased blood

flow

l Cardiovascular insufficiency

l Tissue hypoxia

l Multiple organ failure


Ungraded Practice Question

Which of the following are indicators of sepsis?

More than one answeris c orrec t. Plea se selec t a ll c orrec t a nsw ers

gfedc Erythrocytosis

gfedc Increased heart rate

gfedc Leukocytosis


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Which of the following are indicators of sepsis?

gfedc Increased body temperature

More than one answeris c orrec t. Plea se selec t a ll c orrec t a nsw ers

Feedback

Sepsis results in an immune response by the body. This response inc ludes increasing body temperature and leukocytes in order to

help fight off the infection, and increased heart rate in order to get more blood a nd oxygen to the tissues.

Erythrocytosis is not part of the immune response.

Laboratory Tests Used in the Detection of Sepsi

Biomarkers

An idea l biomarker for diagnosis of disease has these properties:

l High sensitivity (accurately identifies the presence of disease and has few fa lse-negatives)

l High specificity (accurately detects the absence of disease and has few false-positives)

l Relates to the extent of disease

l Changes as the clinical condition evolves

A biomarker that is able to identify sepsis, or determine which patients with sepsis are likely to develop severe sepsis, would be very

useful. However, an ideal marker for sepsis is still not availab le.

C -reactive protein (CRP), proca lcitonin (PCT), and lactic ac id (lactate) are c urrently the tests that are most often used to a id in the

detec tion of sepsis. However, test specificities and sensitivities are not high and if these tests are used to presumptively diagnose

sepsis prior to ava ilability of the blood c ulture or other culture reports, the results must be interpreted along with the c linical

assessment.

As mentioned earlier in the course, sepsis may include these symptoms:

l A body temperature >38C or 90 beats/minute

l Respiratory rate >20 breaths/minute

l An a lteration in the white blood cell (WBC) picture, such as a c ount >12.0 x 109/L or < 4.0 x 109/L or >10% immature neutrophi

l Altered mental status

gfedc Erythrocytosis

gfedc Increased heart rate

gfedc Leukocytosis

gfedc Increased body temperature


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l Edema

l Hyperglycemia in the absence of diabetes

l Elevated CRP

l Elevated PCT

l Elevated lactic ac id (septic shock)


Glucose

Hyperglycemia commonly develops in sepsis; it is a part of the bodys inflammatory response as well as a common response to

stress. However, hyperglycemia does not always develop with sepsis, and in some patients, it may develop even in mild

disease. Therefore, it cannot be considered a reliable biomarker as it lacks both specificity and sensitivity. It may be used along

with other indica tors to identify sepsis.


C-Reactive Protein (CRP)

CRP begins to rise within 4-6 hours after stimulus from an inflammation/ infection. The level doubles every eight hours and peaks

at 36-50 hours.

CRP is a sensitive marker of inflammation and tissue damage. However, it has a low specificity. Conditions other than sepsis

that can cause a rise in CRP levels include:

l Rheumatic diseases

Systemic lupus erythematosus

Systemic sclerosis

Sjogren syndrome

l Inflammatory bowel disease

l Leukemia

l Transfusion assoc iated graft-vs-host disease

Once the determination has been made that sepsis is present and therapy has been initiated, CRP is useful for monitoring response

to antibiotics and predicting prognosis.


Procalcitonin (PCT)

PCT increases early in infection and has a greater specificity for infection than CRP. Increased PCT can be observed within 3-6

hours of infection.

PCT enables the differentiation between a severe bacterial infection and other clinical conditions that may be c ausing a

systemic inflammatory response, allowing antibiotic treatment to begin sooner. Elevated PC T values generally correlate well


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with positive blood and other culture results. Depending on the clinica l assessment, a PC T conc entration >0.1 ng/ mL (reference

value


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Lactic Acid (Lactate), continued

Hyperlac temia in patients with sepsis is an indicator of the severity of stress response. Hyperlac temia may possibly develop as a

byproduct of overall acceleration in glycolysis in severe sepsis. This may well be an adaptive host mechanism designed to

provide for efficient generation of energy in response to severe stress. However, some investigators have observed thatpatients with sepsis have decreased lactate c learance rather than increased lac tate production. Skeletal muscle and lung

tissue have been shown to produce lactate during sepsis. Therefore, hyperlactemia may be caused by increased lactate

produc tion in the gut, liver, lungs, and skeletal muscles, decreased lactate c learance in the liver, or a combination of both.



Which of the following statements regarding a biomarker with high sensitivity is true?

Plea se selec t the single b est answer



Which of the following statements regarding a biomarker with high sensitivity is true?

nmlkj Accurately identifies the presence of disease and has few false-negatives

nmlkj Ac curately identifies the presence of disease and has few false-positives

nmlkj Accurately detec ts the absence of disease and has few false-negatives

nmlkj Accurately detects the absence of disease and has few false-positives


Feedback

A biomarker with high sensitivity ac curately identifies the presence of disease and has few false-negatives.

A biomarker with high specificity accurately detects the absence of disease and has few false-positives.

nmlkj Accurately identifies the presence of disease and has few false-negatives

nmlkj Ac curately identifies the presence of disease and has few false-positives

nmlkj Accurately detec ts the absence of disease and has few false-negatives

nmlkj Accurately detects the absence of disease and has few false-positives


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C-reactive protein (CRP) is more useful for monitoring response to antibiotics and predicting prognosis than for ac tual

diagnosis of sepsis.

Selec t true or fa lse



C-reactive protein (CRP) is more useful for monitoring response to antibiotics and predicting prognosis than for ac tual

diagnosis of sepsis.

nmlkj True

nmlkj False


Feedback

CRP is a sensitive marker for detec tion and monitoring progression of inflammation and tissue damage. However, CRP lacks

specificity. Once a diagnosis of sepsis has been made and therapy has been initiated, CRP is useful for monitoring response to

antibiotics and predicting prognosis.



Of the three laboratory tests that are listed, which has proven to be most effective for early differentiation of systemic

inflammatory response syndrome (SIRS) from sepsis due to its increase following infection and higher spec ificity?

nmlkj True

nmlkj False


nmlkj C-reactive protein (CRP)

nmlkj Procalcitonin (PCT)

nmlkj Lac tic ac id


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Of the three laboratory tests that are listed, which has proven to be most effective for early differentiation of systemic

inflammatory response syndrome (SIRS) from sepsis due to its increase following infection and higher spec ificity?


Feedback

PCT usually rises within 3-6 hours of infec tion. CRP also increases rap idly following infec tion, but is not as specific for infection as PCT

A rise in CRP could a lso occur with SIRS. Lactic acid is usually used to detec t and monitor impaired circulation and tissue

oxygenation in critica lly ill patients..



Blood lactic ac id concentration is an indicator of impaired circulation and tissue oxygenation in c ritically ill patients. If

c irculation and tissue oxygenation are impaired, blood lactic ac id concentration will dec rease below the lower end of theestablished reference range.

nmlkj C-reactive protein (CRP)

nmlkj Procalcitonin (PCT)

nmlkj Lac tic ac id




Blood lactic ac id concentration is an indicator of impaired circulation and tissue oxygenation in c ritically ill patients. If

c irculation and tissue oxygenation are impaired, blood lactic ac id concentration will dec rease below the lower end of the

established reference range.

nmlkj True

nmlkj False


nmlkj True

nmlkj False


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Feedback

The statement is false. Lac tic acid will increase. When cells do not receive enough oxygen because they are not receiving enough

blood, they release excess lactic ac id into the bloodstream. Organ failure as a result of septic shock may be indicated by

unexplained metabolic acidosis (low blood pH and low bicarbonate level) and extremely elevated lactic acid, where blood pH is

1.5 times the upper limit of the laboratorys established reference values.

Mechanisms of C-Reactive Protein, Procalcitonin, and Lactic Ac id

Mechanism of C-Reactive Protein (CRP)

CRP is an a cute phase reactant that is synthesized in the liver. Serum CRP levels increase following a variety of pro-

inflammatory events such as infection, tissue necrosis, trauma, surgery, and malignancy. CRP levels can increase quickly and

dramatica lly (often 100-fold) during inflammation. CRP can ac tivate complement, bind Fc receptors and can function as an

opsonin, enhanc ing phagocytosis with certain infections.


Mechanism of Procalcitonin (PCT)

PCT is a precursor of the hormone calcitonin and is synthesized

physiologica lly by thyroid C cells. PCT levels are low in

homeostatic c onditions. In bac terial infec tions, PCT is synthesized

in various extrathyroida l neuroendocrine tissues. Overall, PC T

secretion is a component of the inflammatory response thatappears to be relatively specific to systemic bac terial infections.

PCT is a 116-amino acid polypeptide precursor to the c alcium

regulatory hormone calcitonin. It is composed of three sec tions

(see image on the right):

l The amino terminus (N-ProCT)

l Immature calc itonin

l Katacalcin

Synthesis of PCT is regulated by the Ca lc -1gene located on

chromosome 11. In healthy individuals, production of PCT, and

subsequently calcitonin, is restricted to the thyroid C cells.


Mechanism of Lactic Acid (Lactate)

Pyruvate is the normal end-product of glycolysis (glucose metabolism). In


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the presence of oxygen, pyruvate is converted to acetyl-coenzyme A

(CoA), which ultimately produces energy in the form of ATP. However, in

an oxygen-deficient environment, CoA is not produc ed and pyruvate is

converted to lactate through anaerobic metabolism. The quantitative

measurement of lactic acid in plasma indicates the severity of oxygen

deprivation.

An elevated lactate is known to be assoc iated with increased mortality

rates. If the lactate c an be cleared, prognosis improves.

Patients who develop severe sepsis or septic shock commonly

demonstrate hyperlac temia and lac tic ac idosis. Increased lac tateproduction during anaerobic metabolism and dec reased lac tate

clearance are likely contributors to hyperlactemia.


Other Causes of Increased Lactic Acid (Lactate) Concentration

Lac tate can a lso be increased, even when there is no evidence of oxygen deprivation. Increased lactate can occur if patients

have decreased ac tivity of the enzyme pyruvate dehydrogenase or impaired clearance of lactate as a result of hepatic

dysfunction.

Plasma lactate concentration can be falsely increased if the plasma is not separated from the cells shortly after sample

collection (Centrifugation a nd separation of plasma from cells is recommended within 15 minutes of c ollection). Blood cells

continue to metabolize glucose following c ollection, resulting in the produc tion of lactic ac id. For this reason, a gray-top tube

containing sodium fluoride, which inhibits glycolysis, is usually rec ommended for plasma lactate sample collection. Other

preanalytic errors that may also produce falsely increased lactate concentrations include: tourniquet usage during specimen

collection combined with patient clenching and unc lenching his/her fist and specimen hemolysis. It is also recommended that the

blood specimen is plac ed on ice immediately after collection to further inhibit glycolysis and lactic ac id formation.



In healthy individua ls, procalcitonin is synthesized by which cells in the body?


nmlk Hepatocytes


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In healthy individua ls, procalcitonin is synthesized by which cells in the body?

nmlkj Leukocytes

nmlkj Thyroid C cells

nmlkj Red blood c ells


Feedback

In healthy individuals, procalc itonin is only synthesized by the thyroid C cells. In bac terial infections, PCT is synthesized in various

extrathyroidal neuroendoc rine tissues.

Future Perspective

Increase in Sepsis Cases

The incidence of sepsis is reportedly increasing by 8% annually (adjusting for population). The highest increases in cases of severe

sepsis are reported in older adults and the nonwhite population. The rise in the number of cases is believed to be caused by:

l Immunosuppresive conditions, including HIV/AIDS, cancer, and solid organ tumors

l Increased use of invasive procedures

l Immunosuppressive drugs

l Chemotherapy

l Organ transplantationl Prosthetic implants

l Antimicrobial resistanc e

Age is a risk factor in itself, even without an underlying medical c ondition. With the aging of the "baby boomer" generation, the

United States will soon have a larger group of people over the age of 65 than it has every had before in the history of the country.

The number of people over the age of 65 in 2030 is predicted to be double what it was in 2000. Oltermann has dubbed this

potential occurrence the "sepsis boom."*

*Reference: O ltermann MH. The coming "sepsis boom...". MLO on l ine. Available at: http:/ /www.mlo-online.com/articles/201202/the

coming-and-ldquosepsis-boom-and-rdquo.php. Ac cessed Oc tober 30, 2012.

nmlkj Hepatocytes

nmlkj Leukocytes

nmlkjThyroid C cells

nmlkj Red blood c ells
http://www.mlo-online.com/articles/201202/the-coming-and-ldquosepsis-boom-and-rdquo.php


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Future Perspective

Novel Biomarkers That Focus on Immunosuppression

With the rise in oc currenc e of sepsis, it is more important than ever to identify biomarkers that can be used for early detection

of severe sepsis. Some researchers have been focusing on the transition that occurs from sepsis (overreac tion by the immune

system) to severe sepsis (immunosuppression) and the a lterations in monoc ytes and T cells that are charac teristic of the

immunosuppressive phase of severe sepsis.

Research has determined that circulating monoc ytes from patients with severe sepsis have decreased amounts of major

histocompatibility complex (MHC) class II proteins on their surfac es and circulating T cells have significantly increased C TLA-4 ligand.

It is yet to be determined if these facts can translate to useful biomarkers for early identification of severe sepsis. Flow cytometry may

be the laboratory method of choice, if changes in circulating monocytes and T cells provide the ideal biomarkers for early

detection of severe sepsis.

Reference

References

Angus DC, Linde-Zwirble WT, Lidicker J , et al. Epidemiology of severe sepsis in the United States: Analysis of incidenc e, outcome,

and assoc iated c osts of care. Cr it Ca re Me d .2001;29:1303-1310.

Castelli GP, Pognani C, Meisner M, et a l. Proc alcitonin and C-reactive protein during systemic inflammatory response

syndrome, sepsis, and organ dysfunction. Available at: http://ccforum.com/content/8/4/R234. Ac cessed Oc tober 30, 2012.

Faix J . Sepsis: New a pproaches to diagnosis and treatment. Cl in Lab New s. July 2012;38(7):12-14.

Harbarth S, Holec kova K, Froidevaux C, et al. Geneva Sepsis Network. Diagnostic value of procalcitonin, interleukin-6, and

interleukin-8 in critically ill patients admitted with suspected sepsis. Am J Resp ir Cri t Ca re Me d. 2001;164:396-402.

LaRosa SP. Sepsis. Cleveland C linic website. Ava ilab le at:

http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/infectious-disease/sepsis/#s0050. Accessed October 30

2012.

Mller B, Becker KL, Schchinger H, et al. Calcitonin precursors are reliable markers of sepsis in a medical intensive care unit.Cri t

C a r e Med. 2000;28(4):977-983. .

Oltermann MH. The coming "sepsis boom...". MLO on l ine . Available at: http:/ /www.mlo-online.com/articles/201202/the-coming-

and-ldquosepsis-boom-and-rdquo.php. Ac cessed Oc tober 30, 2012.
http://ccforum.com/content/8/4/R234http://ccforum.com/content/8/4/R234http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/infectious-disease/sepsis/#s0050http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/infectious-disease/sepsis/#s0050http://www.mlo-online.com/articles/201202/the-coming-and-ldquosepsis-boom-and-rdquo.phphttp://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/infectious-disease/sepsis/#s0050http://ccforum.com/content/8/4/R234

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