Investigations
1st investigations to order
blood culture
Test
The most common method of establishing the diagnosis, although sensitivity ranges from 20% to 80%. A positive culture is always significant and is not considered a contaminant. A negative blood culture does not rule out the diagnosis in the appropriate clinical setting.
Fungal blood cultures have been considered to be more sensitive than routine blood cultures, but advancements in automated blood culture systems have made these specialised cultures largely unnecessary for most patients. May be used to supplement routine blood cultures.
Result
positive or negative
FBC
Test
WBC count is sensitive but not specific for the diagnosis of sepsis.
Thrombocytopenia of non-haemorrhagic origin may occur in patients who are are severely ill with sepsis.
Result
WBC count 12 x 10^9/L (>12,000/microlitre) or <4 x 10^9/L (>4000/microlitre), low platelets
ABG
Test
Should be performed if sepsis suspected.
Blood gas evaluation facilitates optimisation of oxygenation.
Differentiation of respiratory from metabolic acidosis allows metabolic demands to be identified and treated.
Repeat blood gases are indicated depending on the clinical state of the patient.
Result
hypoxaemia, hypercapnia
lactate levels
Test
Should be performed if sepsis suspected.
Venous and/or arterial blood may be sampled.
Lactate levels are an index of global inadequate tissue perfusion.
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.
Result
hyperlactataemia: 2 to 5 mmol/L; shock: ≥4 mmol/L
coagulation studies
Test
Initial test performed in patients with suspected sepsis. Should be done before central line placement.
Result
prolonged INR, PTT, and PT
renal function tests
Test
Should be performed if sepsis suspected.
Elevated creatinine is a sign of sepsis.
Result
creatinine twice normal
liver function test
Test
Should be performed if sepsis suspected.
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 alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma glutamyl transpeptidase, and bilirubin
serum glucose
Test
Should be performed if sepsis suspected.
Result
may be elevated, or more rarely, low
Investigations to consider
1,3-beta-D-glucan
Test
FDA-approved as an adjunct for the diagnosis of systemic candidiasis. However, limited experience in clinical use. False-positive results may occur with antibiotics, surgical gauze, haemodialysis, or use of intravenous immunoglobulin. High levels may be more specific (>500 picogram/mL). However, negative predictive value is good.[27][29][35][36]
Result
positive result may indicate systemic infection
T2 magnetic resonance assay
tissue biopsy
Test
Considered definitive evidence of invasive candidiasis, regardless of source.
Result
yeast forms or pseudohyphae seen in tissue
Emerging tests
polymerase chain reaction
Test
Although there have been reports of successful use of polymerase chain reaction and increased sensitivity compared with blood cultures, it is not widely commercially available.[33]
Result
identification of Candida DNA
matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry
Test
Cultures from patient samples are ionised and matched to a reference organism database for identification. The FDA has approved use of a MALDI-TOF system to identify C auris in the US.[34]
Result
identification of Candida species
Use of this content is subject to our disclaimer