Tests
1st tests to order
CBC
comprehensive metabolic panel
Test
Sodium <135 mEq/mL is present in nearly 100% of the patients with gangrene on admission.[43]
Result
may indicate metabolic acidosis, liver derangement, renal failure
serum LDH
coagulation panel
Test
Perform as baseline.
Result
normal
blood cultures
Test
Recommended if infectious gangrene is suspected.
Result
positive for infective organism
serum CRP
Test
CRP >150 mg/L is highly suggestive of necrotizing soft-tissue infections in an appropriate clinical scenario.
Result
elevated
plain x-rays
Test
Specificity of 95% for gas gangrene, but present in only 10% to 15% of the patients with the condition on admission.[43]
Result
may demonstrate gas in the soft tissues and/or indicate underlying osteomyelitis
CT of affected site
Test
CT scanning is helpful, especially in abdominal cases of gas gangrene.[5] The absence of abnormal findings in the fascia makes necrotizing fasciitis less likely; its presence, however, may also occur with simple cellulitis.[38]
Result
may reveal abscess formation or of enhancement, edema, or thickening in the fascia
MRI of affected site
Test
A lack of demonstrable gas in the soft tissue does not exclude a diagnosis of a necrotizing infection.
Result
may reveal abscess formation or evidence of enhancement, edema, or thickening in the fascia
Doppler ultrasonography
Test
A change in the Doppler waveform from triphasic to biphasic to monophasic and then stenotic waveforms can identify sites of arterial blockage.[9]
Result
may indicate presence and severity of arterial or venous obstruction
Tests to consider
surgical exploration and skin biopsy
CT angiography
Test
If available, CT angiography may be used to look for presence of atheroemboli. CT angiography is increasingly used, but it still requires intravenous contrast, although there is less radiation than with traditional angiography. It can also reconstruct the images into 3D images. The new 64-slice CT images can have sensitivity from 89% to 100% and specificity from 92% to 100% for a greater than 50% stenosis. However, its spatial resolution is lower than digital subtraction angiography and venous opacification can obscure arterial filling.
Result
may show source of atheromatous emboli or specific sites of obstruction
magnetic resonance angiography (MRA)
Test
Less widely available, the sensitivity and specificity of MRA to detect a stenosis greater than 50% can be as high as 90% to 100% with the greatest accuracy when gadolinium is used. However, it does have several limitations: MRA tends to overestimate stenosis and occlusions; metal clips can mimic occlusions thus limiting its use in post surgical patients. Also, patients with pacemakers, defibrillators, and some cerebral aneurysm clips cannot be scanned safely, and gadolinium has caused nephrogenic systemic fibrosis (NSF) in patients with chronic renal insufficiency.
Result
may show source of atheromatous emboli or specific sites of obstruction
CT chest and abdomen
Test
May be useful in detecting a suspected malignancy.[43]
Result
useful in detecting suspected malignancy
antinuclear antibodies (ANA), lupus anticoagulant, anticardiolipin, and anti beta2 glycoprotein-1 antibodies
Test
May be indicated in a patient with suspected ischemic gangrene.
Result
elevated if antiphospholipid syndrome
serum cold agglutinins
Test
May be indicated in a patient with suspected ischemic gangrene.
Result
elevated if cold agglutinin disease
serum cryofibrinogens
Test
May be indicated in a patient with suspected ischemic gangrene.
Result
elevated in cases of cryofibrinogenemia
plasma cryoglobulin
Test
May be indicated in a patient with suspected ischemic gangrene.
Result
positive if cryoglobulinemia
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