Tests
1st tests to order
clinical diagnosis
Test
The diagnosis of diabetes-related foot disease is based primarily on a thorough, structured clinical examination, which should be performed in all patients with newly diagnosed diabetes. Examination should be repeated lifelong at regular intervals, as determined by risk stratification systems, guidelines and local screening protocols.[22][38]
Result
may show ulcers or pre-ulcerative skin lesions, bone or joint deformities, impaired sensation or proprioception, weak or absent pulses, and/or signs of infection, inflammation or ischemia
Tests to consider
CBC
Test
Ordered in all patients with suspected diabetic foot infection as part of IWGDF/IDSA system for classifying infection severity. WBC count correlates poorly with infection severity.[41]
Result
may show leukocytosis
blood glucose level
Test
Ordered in all patients with suspected diabetic foot infection. Often elevated in the presence of infection.
Result
may be elevated
CRP
erythrocyte sedimentation rate
x-ray foot
Test
To be considered if the clinical examination is suggestive of any bone or joint deformities, fractures, osteomyelitis, or Charcot neuro-osteoarthropathy. Weight-bearing films should be considered whenever feasible, especially in patients with Charcot neuro-osteoarthropathy.[8][41][47]
Result
may show hypolucencies, cortical destruction/osteolysis, and/or joint subluxation
microbiologic culture
Test
If a diabetic foot infection is suspected, a tissue specimen should be collected from the base of the wound via curettage or biopsy and sent for culture.[41] Although more burdensome to collect, tissue specimens provide culture results with higher specificity and sensitivity than superficial swabs.[41]
In low-resource settings, a Gram-stain smear may be used as an alternative to culture to visualize the class of causative pathogen.[41] Do not take samples for culture if the wound is not clinically infected. False positive culture results may lead to the unnecessary prescription of antibiotics, which could cause harmful side effects and promote antibiotic resistance.[46]
Result
positive for causative organism in infection, sensitivities may guide antibiotic treatment
renal function
ankle/toe pressures
Test
Should be ordered in patients with a diabetic foot ulcer and a history and examination suggestive of PAD, particularly when the physical exam finds anything other than clearly palpable pulses (e.g., weak pulses, exam limited by edema). Ankle pressures may be spuriously elevated because of arterial calcification and thus should be augmented by toe systolic pressures.[22][50]
Joint guidelines from the International Working Group on the Diabetic Foot, European Society for Vascular Surgery and Society for Vascular Surgery note that no one test has been found to reliably exclude PAD in patients with a diabetic foot ulcer. Its guidelines recommend evaluation of pedal Doppler waveforms in combination with ankle systolic pressure, ankle-brachial index, toe systolic pressure, and toe-brachial index.[10]
Result
toe systolic pressures <30 mmHg are suggestive of PAD and poor ulcer healing. ABI reduced if PAD present; PAD is less likely if ABI is 0.9 to 1.3, TBI is ≥0.70, and triphasic or biphasic pedal Doppler waveforms are present
angiography
Test
Considered to be the best test for diagnosing peripheral artery disease.
May also provide the opportunity for endovascular intervention.
Imaging should extend all the way from the aorta to the foot, with detailed imaging of the tibial and pedal vessels in particular.[10]
Decisions regarding the need for angiography should generally be made by a vascular specialist.
Result
hemodynamically significant (i.e., >50%) stenosis or occlusions between the aorta and the foot (if peripheral artery disease present)
MRI foot
Test
Considered the best imaging test for diagnosing osteomyelitis.
May be more accurate in setting of adequate arterial perfusion (i.e., without peripheral artery disease or after revascularization).
Also useful for diagnosis of soft-tissue infection if diagnosis is not evident from physical exam.
Result
hypointense areas of bone on T1 sequences; hyperintense areas of bone on T2 sequences; soft-tissue fluid collections (if osteomyelitis present)
Emerging tests
serum procalcitonin
CT angiography
Test
Poorer diagnostic accuracy compared with angiography due to the perigeniculate/infrageniculate distribution of atherosclerotic lesions common in patients with diabetes mellitus and foot ulcers (because of inferior spatial resolution) and vessel wall calcification.
Result
depiction of the foot arterial tree and accurate detection of hemodynamically significant (i.e., >50%) stenosis or occlusions between the aorta and the foot (if peripheral artery disease present)
MR angiography
Test
Can be used to obtain anatomical information when considering revascularizing a patient's lower extremity, but does not define the extent of calcification within arteries.[10]
Result
depiction of the foot arterial tree and accurate detection of hemodynamically significant (i.e., >50%) stenosis or occlusions between the aorta and the foot (if peripheral artery disease present)
intra-arterial digital subtraction angiography
Test
Gold standard imaging technique, especially for arteries below the knee and foot, but not as widely available as other modalities. Often used when CT or MR angiography are unavailable, fail to clearly define the anatomy, or when endovascular intervention is planned.[10]
Result
depiction of the foot arterial tree and accurate detection of hemodynamically significant (i.e., >50%) stenosis or occlusions between the aorta and the foot (if peripheral artery disease present)
18F-fluorodeoxyglucose (FDG)-PET/CT
Test
Can be considered as an alternative to MRI for diagnosing diabetes-related osteomyelitis of the foot, if MRI is contraindicated.[41]
Result
may support a diagnosis of osteomyelitis
99mTc-exametazime hexa methyl propylene amine oxime (HMPAO)-labeled white blood cell scintigraphy
Test
Can be considered as an alternative to MRI for diagnosing diabetes-related osteomyelitis of the foot, if MRI is contraindicated.[41]
Result
may support a diagnosis of osteomyelitis
99mTc-labeled ubiquicidin (UBI) SPECT/CT single photon emission computed tomography (SPECT/CT)
Test
Can be considered as an alternative to MRI for diagnosing diabetes-related osteomyelitis of the foot, if MRI is contraindicated.[41]
Result
may support a diagnosis of osteomyelitis
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