3.1 Vascular, Laboratory, Imaging, and Perfusion Studies

Why the focused exam still comes before the lab slip

CWCN items on diagnostic studies (skill 010103 and knowledge 010202) and lower-extremity perfusion (pieces of skill 010311) do not ask you to operate an angiography suite. They ask whether you recognize when a study is indicated, what a common result means for local care, and when to stop and get vascular, infectious-disease, or surgical help. A heel ulcer in a person with diabetes can look like a pressure injury until you notice an absent posterior tibial Doppler signal. A gaiter-region ulcer can look venous until elevational pallor and an ABI of 0.46 tell you that high compression would be harmful.

Recommend a test when the answer will change compression, offloading, debridement, antibiotic choice, or the need for revascularization or biopsy. Do not order a panel because a pathway checkbox exists. Document the clinical question you are asking ("Is there enough arterial inflow for multilayer wrap?" or "Is there osteomyelitis under this probe-to-bone ulcer?") so the result can be interpreted instead of merely filed.

Bedside perfusion: what you can see, feel, and time

Start with both legs, shoes and socks off, room warm enough that vasoconstriction is not the whole story.

Pulses. Palpate the dorsalis pedis (DP) on the dorsum of the foot between the extensor hallucis longus and extensor digitorum longus tendons, and the posterior tibial (PT) just behind the medial malleolus. Grade them consistently (for example 0 absent, 1+ diminished, 2+ normal, 3+ bounding) and compare sides. A bounding, incompressible vessel can coexist with poor microvascular flow in calcified arteries—do not call that "great circulation." If a pulse is not palpable, listen with a handheld Doppler before you write "no flow." Monophasic signals are more concerning than triphasic or biphasic signals when the rest of the exam fits ischemia.

Capillary refill. Press a distal pulp or periungual skin until it blanches, then time return of color. Many wound services use less than about 3 seconds as a usual finding. Prolonged refill supports arterial compromise, but cold rooms, edema, anemia, and dark skin pigmentation all limit the test. Use it as one clue, not a stand-alone rule-out.

Elevational pallor and dependent rubor. Raise the leg (often about 45–60 degrees) for 30–60 seconds. Marked pallor of the foot suggests arterial insufficiency. Then hang the leg dependent: a dusky brick-red dependent rubor that takes many seconds to appear, and that blanches when the leg is raised again, is a classic ischemic pattern. Dependent rubor is not the same as cellulitis; cellulitis is usually warmer, more tender, and not so quickly abolished by elevation.

Hair, nails, and temperature. Loss of hair on the toes, thickened dystrophic nails, shiny taut skin, and a foot that is cooler than the contralateral limb support chronic ischemia. Warmth with erythema may be infection, acute Charcot neuro-osteoarthropathy, or deep inflammation—so temperature is interpreted with pulses, pain, and white-cell or glucose context, not in isolation.

ABI: method overview and wound-care bands

Ankle-brachial index is a ratio of systolic pressures: the higher ankle systolic pressure on that leg (DP or PT) divided by the higher of the two brachial systolic pressures. The patient should be supine and rested (about 10 minutes is a common lab practice) with appropriately sized cuffs. You need a Doppler, not a stethoscope, at the ankle. Skip or modify the test per facility rules if there is acute deep-vein thrombosis, severe rest pain that cannot tolerate cuff inflation, or a fresh bypass graft in the field.

Wound-care interpretation bands you should be ready to apply—and to correlate with the limb in front of you—are:

Two traps appear constantly on exams and on the floor. First, vascular screening papers often call ABI ≤0.90 abnormal, so a "borderline" 0.84 is not a free pass. Second, a high ABI is a calcification warning, especially in diabetes and chronic kidney disease, not a gold-star perfusion score.

TBI when the ankle number lies

Toe-brachial index uses a small-digit cuff, usually on the hallux or second toe, and divides toe systolic pressure by the higher brachial pressure. Digital arteries calcify less often than the ankle vessels, so TBI is the usual next noninvasive test when ABI is incompressible, unmeasurable because of a wound under the cuff, or discordant in a person with diabetes. A TBI under 0.70 is commonly interpreted as abnormal. Very low absolute toe pressures (values in the neighborhood of under 30 mmHg are frequently cited as critical) predict poor healing and should trigger vascular referral rather than another month of the same foam dressing. If the hallux is amputated, use another toe and document which one.

TcPO2, healing potential, and hyperbaric questions

Transcutaneous oxygen (TcPO2) estimates local tissue oxygenation with a heated electrode on intact peri-wound skin, away from bone and heavy edema when possible. Wound services commonly cite values under 40 mmHg as impaired oxygenation and values at or above that range as more compatible with healing—teach those figures as commonly used thresholds, not as a universal law. Other groups (including some diabetic-foot documents) discuss lower cut points such as 25 mmHg when estimating healing probability. Hyperbaric oxygen therapy candidacy often adds a room-air versus 100% oxygen challenge and looks for a meaningful rise; follow the facility and hyperbaric program protocol rather than inventing a single national number. A low TcPO2 supports the story of ischemia or microcirculatory failure; it does not, by itself, diagnose osteomyelitis or replace a pulse exam.

Venous duplex, plain films, MRI, and labs that change management

Duplex ultrasound is the practical test when you need to know whether there is superficial or deep reflux, obstruction, or acute thrombus before you commit to long-term compression or worry that a sudden swollen leg is more than chronic venous disease. Reverse flow after distal compression or Valsalva is interpreted against the vascular lab's reflux-duration criteria (superficial veins are often read as reflux at about 0.5 seconds of reverse flow; deep-vein thresholds are typically longer). You recommend the study and use the report; you do not personally grade every waveform.

Plain radiographs are first-line when you need a rapid look for soft-tissue gas or established osteomyelitis (cortical lucency, periosteal reaction). Bony changes can lag 10–14 days behind infection, so a "normal" film does not clear early osteomyelitis. Gas plus pain out of proportion, crepitus, or rapid spread is a surgical emergency; do not wait for MRI if necrotizing infection is the working diagnosis.

MRI is the usual next imaging step when you suspect deeper infection, abscess, or osteomyelitis that plain films do not settle, provided the patient can complete the study. Probe-to-bone remains a powerful bedside clue in diabetic foot ulcers, but imaging and, when it will change surgery or antibiotic duration, bone biopsy still sit above a swab.

Laboratories support the story; they do not replace it.

• CBC: leukocytosis supports systemic infection but local wound infection can exist with a normal white count, especially in older adults and people with diabetes.
• CRP and ESR: context tests. CRP rises and falls faster; ESR is slower and stays up with anemia or chronic inflammation. Neither value alone proves osteomyelitis, though serial CRP can help you watch treatment response.
• Glucose and A1C: hyperglycemia impairs neutrophil function. A1C reflects roughly three months of glycemia and helps you explain delayed diabetic-foot healing; it is not a wound-bed measurement.
• Renal panel: needed before many antibiotics and contrast studies, and it frames calciphylaxis or volume issues.
• Nutrition markers: albumin and prealbumin fall as negative acute-phase reactants. A low albumin in a septic, draining wound is not a shopping list for protein powder by itself. Pair labs with weight trend, intake, and inflammation.

When the wound needs a biopsy, not another dressing

Recommend tissue biopsy (and dermatology or surgery partnership) when the history is atypical: wrong location for pressure, venous, arterial, or neuropathic disease; pathergy after minor trauma (classic worry for pyoderma gangrenosum); failure to heal despite appropriate etiology-based care; suspected malignancy such as a Marjolin ulcer (squamous cell carcinoma in a chronic wound or scar, often with heaped or rolled edges after years of ulceration); vasculitis (palpable purpura, livedo, punched-out lesions in crops); or suspected pyoderma gangrenosum (painful undermining violaceous border). For inflammatory ulcers, biopsy planning is coordinated so that aggressive wide debridement is not mistaken for "wound bed preparation."

Scenario: the "excellent" ABI that was not excellent

A 71-year-old man with diabetes, an eGFR of 22 mL/min, and a 2-month non-healing lateral heel ulcer is referred for "venous wrap." DP is faintly palpable, PT is absent, the foot is cool, and there is elevational pallor. ABI is 1.44 on that side. A nurse who treats 1.44 as robust flow might apply high compression and convert a stable ulcer into rest pain. The safer CWCN action is to hold high compression, obtain TBI and waveforms, and involve vascular medicine because the ankle vessels are likely calcified and incompressible. If TBI is 0.38 with a monophasic PT signal, the plan shifts toward arterial work-up, heel offloading, and avoiding tight wraps—not toward a four-layer bandage because the ABI looked "high."

Keep the sequence boring and defensible: look and listen first, quantify with ABI/TBI, add duplex or TcPO2 when the question is reflux or oxygenation, image when bone or gas is in play, biopsy when the story is wrong. That is the diagnostic judgment the exam is testing.