Tests
1st tests to order
blood culture
Test
Blood cultures should be taken immediately, and preferably before antibiotics are started, provided their sampling will not delay administration of antibiotics.[10][70][82]
Ideally, at least one set should be taken percutaneously, and one set from any vascular access device that has been in situ for more than 24 hours.[83][84]
Result
may be positive for organism
lactate levels
Test
Elevated serum lactate highlights tissue hypoperfusion, and is assessed using a blood gas sample.[10][112] In practice, a venous blood gas sample is generally used, as it is generally easier and quicker to obtain compared with an arterial blood gas (ABG).
Increasing levels of lactate are associated with increasing levels of anaerobic metabolism.
Persistently elevated lactate levels may parallel the degree of malperfusion or organ failure.
Lactate clearance (the rate at which lactate is cleared over a period of 6 hours) has been demonstrated to be as useful as more invasive tests, such as central venous oxygen saturation, in determining a patient's response to treatment.[91][92]
Result
may be elevated; levels >2 mmol/L (>18 mg/dL) associated with adverse prognosis; even worse prognosis with levels >4 mmol/L (>36 mg/dL)
CBC with differential
Test
WBC count is sensitive but not specific for the diagnosis of sepsis.
Noninfectious injury (e.g., crush injury), cancer, and immunosuppressive agents can also cause either increased or decreased WBC counts.
Thrombocytopenia of nonhemorrhagic origin may occur in patients who are severely ill with sepsis.
Result
WBC count >12,000/microliter (leukocytosis); WBC count <4000/microliter (leukopenia); or a normal WBC count with >10% immature forms; low platelets
blood urea nitrogen (BUN) and serum electrolytes
Test
BUN is performed with serum creatinine to evaluate for renal dysfunction.
Serum electrolytes should be measured at baseline and regularly until the patient improves.
Result
serum electrolytes frequently abnormal; BUN may be elevated
serum creatinine
Test
Elevated serum creatinine may occur in sepsis associated with renal dysfunction.
Result
may be elevated
liver function tests
Test
Baseline test.
Sepsis can originate from hepatic or perihepatic infections.
Comorbidity of underlying hepatic disease can affect drug metabolism and outcome in sepsis.
Septic shock can compromise hepatic blood flow and metabolism, including lactate.
Result
elevated bilirubin, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma glutamyl transferase
coagulation studies (INR, activated PTT)
Test
Baseline test, especially before central line placement.
Result
may be prolonged
serum glucose
Test
May be elevated, with or without known history of diabetes, due to the stress response and to altered glucose metabolism.
Hyperglycemia is associated with increased morbidity and mortality.
Spontaneous or iatrogenic hypoglycemia also poses significant dangers.[113][114]
The Surviving Sepsis Campaign recommends the maintenance of normoglycemia (above lower limit of normal, but <180 mg/dL), preferably with the use of an insulin infusion protocol.[3]
Rarely, glucose may be low, suggesting acute liver failure.
Result
may be elevated or, more rarely, low
CRP
Test
Baseline test. A marker for inflammation. Do not order erythrocyte sedimentation rate (ESR) to detect acute inflammation before a diagnosis has been established; CRP is a more sensitive and specific test for the acute phase of inflammation than ESR.[88]
Result
elevated
other cultures (e.g., of sputum, stool, urine, wounds, catheters, prosthetic implants, epidural sites, pleural or peritoneal fluid)
Test
Other cultures (e.g., of sputum, stool, and urine) should be taken as clinically indicated.
If meningitis is suspected, a lumbar puncture (LP) for cerebrospinal fluid microscopy and culture should be performed. A CT scan prior to performing a LP to exclude raised intracranial pressure is required if there is any clinical suspicion of this.
If an enclosed collection such as an abscess or empyema is suspected, it is recommended that this be drained and cultured early in the course of the illness (within 6-12 hours following identification).[3][85]
Intubated patients in whom there is a suspicion of pneumonia should have tracheal aspirates, bronchoalveolar lavage, or protected brush specimens taken.
If no localizing signs are present, examination and culture of all potential sites of infection, including wounds, urinary and intravenous catheters, prosthetic implants, epidural sites, and pleural or peritoneal fluid, as indicated by the clinical presentation and history, is required.
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Result
may be positive for organism
arterial blood gas (ABG) or venous blood gas (VBG)
Test
ABG evaluation facilitates optimization of oxygenation, and is indicative of metabolic status (acid-base balance).
In ventilated patients, it helps to determine optimal positive end-expiratory pressure (PEEP), while minimizing adverse levels of inspiratory pressure and unnecessarily high FiO₂.
Differentiation of respiratory from metabolic acidosis allows metabolic demands to be identified and treated.
Lactate levels are most reliably assessed using an ABG sample. However, in practice, a VBG sample is usually used, as it is generally easier and quicker to obtain compared with ABG. Most patients do not undergo ABG sampling unless there is a respiratory component.
Repeat blood gases are indicated depending on the clinical state of the patient.
Result
PaCO₂<32 mmHg is one of the diagnostic criteria for systemic inflammatory response syndrome; may be hypoxemia, hypercapnia
chest x-ray
Test
Initial imaging modality required to look for the cause of suspected or confirmed sepsis which can be performed at the bedside.[89]
A chest x-ray is always indicated after central venous pressure and endotracheal tube placement to rule out malposition and complications.
Result
may show evidence of infection, such as consolidation or pleural effusion, cardiac abnormalities, or a pneumothorax
ECG
Test
An ECG should be arranged to help exclude other differential diagnoses, including myocardial infarction, pericarditis, and myocarditis. Sepsis also predisposes to myocardial dysfunction (particularly in septic shock) and arrhythmias (e.g., atrial fibrillation).[10][90]
Result
may show evidence of ischemia, atrial fibrillation, or other arrhythmia; may be normal
Tests to consider
lumbar puncture
Test
Performed if meningitis suspected, provided no suspicion of raised intracranial pressure. A CT scan is required prior to performing a lumbar puncture to exclude elevated intracranial pressure if there is any clinical suspicion of this.
Bacterial meningitis: WBC count elevated; protein is elevated; glucose is normal or reduced; cell differential is predominantly neutrophils.
Viral meningitis may be associated with lower WBC counts and predominant lymphocytes.
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Result
elevated WBC count, presence of organism on microscopy, and positive culture
echocardiogram (transthoracic or transesophageal)
Test
A transthoracic or transesophageal echocardiogram is useful in patients at risk of, or with symptoms compatible with, bacterial endocarditis.
If readily available, may also be appropriate in patients with sepsis of unknown origin.
Also helpful to differentiate between hypovolemic, cardiac, and septic shock.
May determine alternative diagnoses, such as valvular abnormalities, pulmonary embolus, myocardial ischemia, segmental or global dysfunction, hypovolemia, and pulmonary hypertension.
Result
inadequate left ventricular filling suggests hypovolemia; vegetations, if endocarditis is cause of sepsis
ultrasound scan
Test
Including but not limited to abdominal ultrasound scan.
May indicate source of infection (e.g., dilated common bile duct indicating biliary obstruction).
Result
may demonstrate abscess, fluid collection, pneumoperitoneum from perforated viscus, obstruction of gastrointestinal/renal/biliary tracts
CT chest or abdomen
Test
If clinically indicated to establish source of infection.
Requires transfer of potentially unstable patients and the benefit should be weighed against the risk.
Result
abscess, effusion may be demonstrated
serum procalcitonin
Test
Where available, measurement of serum procalcitonin should be considered in all patients with sepsis to guide decisions on when to discontinue antibiotic therapy, alongside clinical evaluation. Among patients with acute respiratory infections (including those resulting in sepsis), procalcitonin-guided therapy was associated with a 2-day reduction in the antibiotic course, a 27% reduction in antibiotic-related side-effects, and a 10% reduction in 30-day mortality rate.[94]
However, evidence for the prognostic value of procalcitonin alone is unclear, and its use in the identification of sepsis is excluded from many guidelines.[3][95][96][97] In addition, changes in procalcitonin levels may occur later than that of lactate, although changes in both markers combined are highly predictive of outcome between 24 and 48 hours.[99] Other pro-inflammatory states, such as acute pancreatitis, trauma, major surgery, and burns, can also increase procalcitonin.
Do not perform procalcitonin testing without an established, evidence-based protocol.[88]
Result
elevated
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