18.2 Referring for Studies and Specialty Consults

The CWCN who orders every test on the menu is not thorough; the CWCN who orders the test that changes compression, surgery, antibiotics, or goals is practicing. Independent OpenExamPrep teaching uses one filter: if the result cannot alter what you do this week, do not delay care to collect it. The same filter applies to consults. A next-Thursday clinic is an appropriate destination for a stable callus and a terrible destination for crepitus and septic shock.

Refer for Studies When the Result Changes the Plan

Ankle-brachial index (ABI) estimates large-vessel perfusion to the foot. Obtain it when you need to know whether compression is safe, whether arterial disease explains delayed healing, or whether a vascular specialist should see the patient now. An ABI under 0.5 is not a trivia number; it supports chronic limb-threatening ischemia (CLTI) when paired with rest pain or tissue loss and belongs on a vascular list, not on a "try a different foam" list. Do not start or escalate high-level compression on a limb whose arterial status is unknown when the history or pulses raise doubt.

Toe-brachial index (TBI) is the study to reach for when ABI is unreliable because vessels are calcified—common in diabetes, chronic kidney disease, and advanced age. A falsely high ABI can hide ischemia. If the question is "can this toe heal?" and the ABI looks strangely normal in a rigid, noncompressible artery, TBI (or another distal perfusion test) is the plan-changing study.

Transcutaneous oxygen (TcPO2) estimates local skin perfusion. Use it when the decision is healing potential or candidacy for adjuncts such as hyperbaric oxygen—not as a substitute for a vascular specialist when rest pain or an ABI under 0.5 already defines CLTI.

Arterial or venous duplex ultrasound maps stenosis, occlusion, and reflux. Order arterial duplex when intervention planning needs anatomy after you have already recognized ischemia. Order venous duplex when the question is whether reflux or obstruction explains a venous leg ulcer and whether a venous procedure is on the table. Duplex is not a reason to postpone source control of an abscess.

Laboratories should answer a decision, not decorate the chart. Hemoglobin A1c matters when diabetes is uncontrolled or undiagnosed and the ulcer is neuropathic. Inflammatory markers and white count support a systemic-infection or osteomyelitis workup; they do not replace a clinical exam. Nutrition laboratories can flag risk but do not by themselves write a feeding plan—that is why the RD referral exists. Wound cultures are for infected wounds when the result will change antibiotics, not for every colonization on a chronic surface.

Imaging is for suspected deep structure involvement or to plan an operation. Probe-to-bone in a DFU raises osteomyelitis concern and should trigger imaging and a specialist path, not another week of topical silver. Plain films may show gas, foreign body, or established bone change; magnetic resonance imaging is often used when osteomyelitis remains the question and the result will change debridement or antibiotic duration. Do not delay the operating room for an MRI when necrotizing infection is the working diagnosis.

Biopsy belongs on atypical, nonhealing, or suspected inflammatory and malignant wounds: a chronic ulcer with heaped edges concerning for Marjolin ulcer, a violaceous undermined border concerning for pyoderma gangrenosum (PG), or a presentation that looks like vasculitis rather than ordinary pressure or venous disease. Biopsy of the appropriate edge, with a dermatology or surgical partner, changes immunosuppression versus wide debridement. Pathergy in PG means aggressive wide excision can enlarge the wound; that is a plan-changing fact, not a trivia fact.

Specialty Consults: Who Owns Which Problem

Surgery is for problems that need an incision, drainage, or operative debridement you cannot finish at the bedside: abscess, necrotizing infection, clinically important dehiscence, and extensive necrosis. Do not park those patients on a "wound clinic in seven days" list.

Vascular is for perfusion that will not support healing or that makes compression unsafe. Rest pain, tissue loss with low ABI or TBI, and dependent rubor with absent pulses are CLTI clues. Foam does not reopen a tibial artery.

Infectious diseases helps when bone or systemic infection will drive prolonged or complex antibiotics, drug resistance, or medical comorbidities. ID does not replace source control. If pus is under pressure, the first call is surgical drainage; antibiotics without drainage fail.

Dermatology owns inflammatory and atypical skin-ulcer diagnoses. PG, vasculitis, and unusual neoplasms are easy to miss if every crater is labeled "pressure."

Podiatry owns the mechanical DFU: offloading (including total contact casts and boots when appropriate), nail and callus care, and deformity that keeps recreating the ulcer. A pretty dressing on a walking plantar wound is a delayed amputation plan.

Plastic surgery is for reconstruction—grafts and flaps—once infection is controlled and perfusion is adequate. Sending an infected, ischemic wound for a flap this afternoon skips the steps that make a flap survive.

Urgent Versus Routine—And the Necrotizing Exception

Routine is for stable, named problems: chronic venous reflux workup, scheduled offloading, a biopsy of a weeks-old atypical edge in a well-appearing patient. Urgent is for same-day or 24-to-48-hour threats: rest pain with tissue loss, an undrained abscess, dehiscence with exposed viscera, wet gangrene, systemic infection with a wound source.

Necrotizing infection is immediate. Pain out of proportion, rapid spread, crepitus, dishwater drainage, and sepsis belong in an operating room pathway now. Broad-spectrum antibiotics and resuscitation start in parallel. What you do not do is book next week's clinic, wait for a perfect MRI, or "have ID see first" while tissue dies. Imaging may help a stable, unclear case; it is not a permission slip to delay surgery when the clinical diagnosis is necrotizing infection.

The diagram below is a consult clock, not a bureaucracy chart. Start with threat to life or limb, then ask whether a test would change the plan, then pick the specialist who treats the cause.

Scenario: The Thursday Clinic Slot

A 64-year-old with diabetes presents from home with a plantar ulcer. Yesterday the wound was a 1 cm opening; today the dorsum is tense, the pain is far out of proportion, and there is crepitus. A well-meaning scheduler offers "wound clinic Thursday and a set of labs." The ABI machine is booked tomorrow. The correct CWCN action is to stop the outpatient sequence, activate an emergency surgical pathway for suspected necrotizing infection, and obtain perfusion studies only after the patient is on an operative track—or not at all if they would delay the knife. Thursday is for callus. This morning is for the operating room.