Keys To The Diagnostic Workup For Patients With Diabetic Foot Infections

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Author(s): 
Valerie L. Schade, DPM, AACFAS, and Nathan S. Higa, DPM, AACFAS

   C reactive protein (CRP). The CRP is a hepatically produced peptide that is released in inflammatory and infectious conditions. A normal CRP level is <10 mg/L.2 Its use as an aid in the diagnosis of moderate or severe diabetic foot infections has not been consistently reported due to the wide range of reported optimal cutoff values, ranging from >3 mg/dL to 100 mg/dL for being diagnostic for the presence of osteomyelitis.3,10,21,22 The value of obtaining a CRP has been more of a supportive role when one combines it with other laboratory studies, physical exam and imaging findings.2

   Procalcitonin. Procalcitonin is a hormone secreted by non-neuroendocrine parenchymal cells. Normal levels are <0.10 mg/mL.2 Procalcitonin can remain low in viral infections and inflammatory diseases, and be more specific to bacterial infections, rising within two hours of onset.2,23,24

   Uzun and colleagues found that procalcitonin, CRP, WBC and ESR were all significantly elevated in patients with diabetes and a skin/soft tissue infection.23 The authors noted a reported sensitivity of 59 percent, specificity of 100 percent, a positive predictive value of 100 percent and a negative predictive value of 67 percent. Mutluogu and co-workers found that an elevated procalcitonin was not as predictive in cases of osteomyelitis.24 When comparing procalcitonin, CRP, ESR and WBC, an elevated ESR was the only laboratory value to play a diagnostic role in the presence of osteomyelitis.

   Hemoglobin A1c (HgBA1c). Hemoglobin A1c gives an estimate of the daily glucose levels of patients over the past 120 days. Recent studies have shown decreased wound healing with HgBA1c levels of less than 7 percent.25,26

   Christman and colleagues found a decrease in daily wound healing by 0.028 cm2 for every 1 percent increase of HgBA1c over 7 percent. This rate decreased to 0.022 cm2 per day in patients with a neuropathic ulcer.25 Aragon-Sanchez and colleagues reported on the importance of perioperative glycemic control in comparison to preoperative glycemic control in reducing the risk of amputation in patients with diabetes and osteomyelitis.26 Obtaining a baseline HgBA1c at admission can help guide perioperative and postoperative glycemic control.

What About Nutritional Markers?

One should assess nutritional status in all patients with diabetes as they are at increased risk for being malnourished.22,27 Adequate nutrition is critical for wound healing. An albumin of >3.5 mg/dL can result in decreased healing times in patients.22 A prealbumin of >15 mg/dL can be the single best predictor of survival in patients on hemodialysis and the best predictor of response in treatment of critically ill patients with sepsis.27

   The half-life of albumin is 14 to 21 days. Prealbumin has a half-life of two to three days. Given its shorter half-life, one can reassess prealbumin every two to three days to determine if implemented measures to boost nutritional status are effective. Rising prealbumin levels indicate that a minimum of 65 percent of nutritional requirements is being provided.27

When Should You Obtain A Wound Culture?

One should only obtain wound cultures for clinically infected ulcers. Intraoperative cultures are preferred. However, one can obtain cultures in the clinical setting if it occurs in the proper fashion. Cleanse the lower extremity and wound with an antimicrobial cleanser both prior to and following adequate debridement of the ulceration. Then insert the culture swab into the depths of the wound.

   Send specimens for gram stain, aerobic and anaerobic culture and sensitivities utilizing the appropriate culture tubes. Consider obtaining fungal cultures in wounds of more than six months duration. Results of fungal cultures can take over four weeks to return. One can send a sample of tissue for a KOH prep to determine the potential need for fungal coverage.

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