Tests
1st tests to order
surgical exploration
Test
If necrotizing fasciitis is suspected clinically, immediate surgical consultation for inspection, exploration, and debridement of infected tissue should be obtained.[3][5]
The "finger test" is a surgical method that can be performed under local anesthesia at the bedside for the diagnosis of necrotizing fasciitis.[2] It involves making a 2 cm incision down to the deep fascia. Findings that suggest necrotizing fasciitis following incision include:[2]
Minimal resistance to finger dissection (a "positive" finger test)
Absence of bleeding
Presence of necrotic tissue
Murky or greyish "dishwater" fluid.
Result
necrotizing soft-tissue infection on surgical exploration, positive finger test, absence of bleeding, presence of necrotic tissue, murky or greyish "dishwater" fluid following incision
blood and tissue cultures
Test
Definitive bacteriologic diagnosis is best made using tissue specimens obtained from surgical debridement and blood cultures.[5]
Result
positive; may indicate polymicrobial or monomicrobial etiology
gram stain
Test
Staining of clinically affected tissue may provide early indication of causative organism(s). For example, small chains of gram-positive cocci suggest a streptococcal infection; clumps of large cocci suggest Staphylococcus aureus.
Result
variable
complete blood count and differential
Test
High WBC is a nonspecific finding that may be seen in any systemic infection or circulatory collapse. A low WBC count may be a sign of severe sepsis. If a spreading soft-tissue infection is present, necrotizing fasciitis should be suspected.[2][3][4][5]
If necrotizing fasciitis is suspected, immediately refer the patient to the surgical team; do not wait for the results of investigations before referral.[2][5] Necrotizing fasciitis is a clinical diagnosis. However, investigations can support the diagnosis if this is unclear.[2]
Result
abnormally high or low WBC count with or without a left shift (elevated percentage of polymorphonuclear leukocytes and/or bands)
serum electrolytes
Test
Hyponatremia is a nonspecific finding that may be seen in any systemic infection or circulatory collapse. If a spreading soft-tissue infection is present, necrotizing fasciitis should be suspected.[2][3][4][5]
If necrotizing fasciitis is suspected, immediately refer the patient to the surgical team; do not wait for the results of investigations before referral.[2][5] Necrotizing fasciitis is a clinical diagnosis. However, investigations can support the diagnosis if this is unclear.[2]
Result
sodium may be decreased
serum BUN and creatinine
Test
A nonspecific finding that may be seen in any systemic infection or circulatory collapse. If a spreading soft-tissue infection is present, necrotizing fasciitis should be suspected.[2][3][4][5]
If necrotizing fasciitis is suspected, immediately refer the patient to the surgical team; do not wait for the results of investigations before referral.[2][5] Necrotizing fasciitis is a clinical diagnosis. However, investigations can support the diagnosis if this is unclear.[2]
Result
serum BUN and creatinine may be elevated
serum CRP
serum creatine kinase (CK)
serum lactate
clotting screen
Test
Used to determine whether the patient has established coagulopathy in the presence of sepsis. This is associated with a worse prognosis.[45]
If you suspect necrotizing fasciitis, immediately refer the patient to the surgical team; do not wait for the results of investigations before referral.[2][3][4][5] Necrotizing fasciitis is a clinical diagnosis. However, investigations can support the diagnosis if this is unclear.[2]
Result
may show coagulopathy
arterial blood gas
Test
Acidosis may be present in the setting of sepsis. May be obtained if there is concern for respiratory compromise.
Helps determine patient's respiratory status.
Result
hypoxemia, acidosis
Tests to consider
radiography, CT/MRI, ultrasound
Test
Imaging studies should not delay surgical intervention when diagnosis is clinically suspected.[2][3][5]
Plain radiography, ultrasound, or CT/MRI (if available) may be obtained in all patients with suspected necrotizing fasciitis, if clinically appropriate.[3][36] Plain radiography is frequently normal during the early stages; subcutaneous gas may be present as the disease progresses. The diagnosis should be strongly suspected if soft-tissue gas is visualized on radiologic exam, which may also demonstrate abnormalities in the involved soft tissue.[1][2][16][36] However, soft-tissue gas is a late sign, and plain radiography has poor sensitivity for detecting signs of necrotizing infection.[15]
Ultrasound may help to differentiate simple cellulitis from necrotizing fasciitis and has the advantage that it can be rapidly performed at bedside.[2] In one prospective study, ultrasound findings of diffuse thickening of the subcutaneous tissue, accompanied by fluid accumulation greater than 4 mm in depth, had a sensitivity of 88% and specificity of 93%.[37]
CT and MRI offer higher sensitivity.[3][36] CT is indicated in abdominoperineal and cervicofacial infections to show the portal of entry of infection and to guide surgical intervention; for limb or peripheral necrotizing soft-tissue CT is of limited value.[15][36] MRI is more sensitive for assessing necrotizing soft-tissue infections of the limbs, and may show thickening of the fascia, deep fascial fluid or edema. However, these signs are not specific to necrotizing infection and may be seen in other soft-tissue infections such as cellulitis, and MRI may be difficult to organize in an emergency and is not recommended as the first-line imaging technique.[2][3][15][38][46]
In a meta-analysis, CT had sensitivity of 88.5% and specificity of 93.3%, while plain radiography had sensitivity of 48.9% and specificity of 94.0% for diagnosing necrotizing soft tissue infections.[39]
Result
edema extending along fascial plane and/or soft tissue gas
fresh frozen section
Test
Early frozen-section soft-tissue biopsy can provide a definitive diagnosis and it may be used if the diagnosis is unclear clinically or radiologically.[2] However, frozen-section soft-tissue biopsy requires specialist pathology expertise, takes time to perform, and is not widely available in all regions.[2]
Result
evidence of bacteria and tissue necrosis
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