Investigations
1st investigations 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.[36]
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 ischaemia
Investigations to consider
FBC
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.[40]
Result
may show leucocytosis
blood glucose level
Test
Ordered in all patients with suspected diabetic foot infection. Often elevated in the presence of infection.
Result
may be elevated
microbiological culture
Test
If a diabetic foot infection is suspected and a wound is present, send soft-tissue or bone samples from the base of the wound for microbiological evaluation.[9] This should ideally be a tissue specimen aseptically collected by curettage or biopsy: although more burdensome to collect, tissue specimens provide culture results with higher specificity and sensitivity than superficial swabs.[40] If this is not possible, NICE recommends that a deep swab be taken as it may provide useful information on the choice of antibiotic treatment.[9]
In low-resource settings, a Gram-stain smear may be used as an alternative to culture to visualise the class of causative pathogen.[40]
Result
positive for causative organism in infection; sensitivities may guide antibiotic treatment
erythrocyte sedimentation rate
Test
May suggest the presence of an infection, especially if highly elevated (≥ 70 mm/h). But accuracy can be affected by comorbidities such as anaemia, and tends to rise slowly so may not be elevated in early acute infections.[40]
Result
elevated
C-reactive protein
renal function
ankle/toe pressures
Test
If physical examination of a patient with a diabetic foot ulcer finds anything other than clearly palpable pulses (e.g., weak pulses, examination limited by oedema), order non-invasive testing of ankle/toe pressures.[11]
The UK National Institute for Health and Care Excellence recommends calculating resting ankle-brachial index (ABI) in patients with suspected peripheral arterial disease (PAD) but warns that a diagnosis of PAD cannot be excluded based solely on a normal or raised ABI result.[9][41]
The International Working Group on the Diabetic Foot notes 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, ABI, toe systolic pressure, and toe brachial index (TBI).[11]
Result
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[11]
x-ray foot
Test
To be considered in all patients, to determine the extent of diabetes-related foot complications, and particularly in any patients with suspected osteomyelitis or Charcot's neuro-osteoarthropathy. Weight-bearing films should be considered whenever feasible, especially in patients with Charcot's neuro-osteoarthropathy.[9][40]
Result
may show hypolucencies, cortical destruction/osteolysis, and/or joint subluxation
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.[11]
Result
haemodynamically 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 revascularising a patient's lower extremity, but does not define the extent of calcification within arteries.[11]
Result
depiction of the foot arterial tree and accurate detection of arterial stenosis
CT angiography
Test
Diagnostic accuracy is affected by the presence of severe arterial calcification.[11]
Result
depiction of the foot arterial tree and accurate detection of arterial stenosis
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.[11]
Result
depiction of the foot arterial tree and accurate detection of arterial stenosis
MRI foot
Test
Considered the best imaging test for diagnosing osteomyelitis.
Result
hypo-intense areas of bone on T1 sequences; hyper-intense areas of bone on T2 sequences (if osteomyelitis present)
arterial duplex ultrasound
Test
Can provide anatomical details and physiological assessment of blood flow at specific arterial sites from the abdominal to the tibial arteries.
It requires specialist equipment and technical expertise to perform.
The UK National Institute for Health and Care Excellence suggests that duplex ultrasound should be offered as first-line imaging to all people with peripheral arterial disease for whom revascularisation is being considered.[41]
Result
assessment of the peripheral arterial circulation helps determine whether peripheral arterial disease is present
Emerging tests
serum procalcitonin
Test
May be elevated in infected diabetic foot ulcers but little correlation with infection severity. Expensive and not available in many laboratories.[40]
Result
may be elevated
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.[40]
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.[40]
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.[40]
Result
may support a diagnosis of osteomyelitis
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