What baseline laboratory tests should be ordered for a patient with a sacral pressure ulcer to evaluate infection, nutritional status, and metabolic factors?

Laboratory Evaluation for Sacral Pressure Ulcers

For any patient with a sacral pressure ulcer, immediately order a complete blood count, albumin, hemoglobin, C-reactive protein, and blood glucose to assess infection risk, nutritional status, and metabolic factors that directly impact wound healing. 1, 2, 3

Mandatory Baseline Laboratory Panel

Infection Assessment

• Complete blood count (CBC) to detect leukocytosis indicating active infection 4
• C-reactive protein (CRP) as a marker of systemic inflammation and infection 4, 3
• Blood cultures are generally not recommended unless there is evidence of systemic infection or sepsis 4

Nutritional Status Evaluation

• Serum albumin to assess protein status and overall prognosis, though it does not precisely define nutritional status 4, 1, 2
• Prealbumin, transferrin, and retinol-binding protein may provide additional prognostic information but similarly do not definitively represent nutritional status 2
• Hemoglobin levels, as higher hemoglobin correlates significantly with wound healing 3

Metabolic Parameters

• Blood glucose monitoring, as hyperglycemia impairs wound healing 3, 5
• Electrolytes, urea, and creatinine for metabolic assessment 4
• Iron studies to evaluate for deficiency 4
• Vitamin B12 levels 4

Critical Pitfalls to Avoid

Do Not Order Surface Swab Cultures

• Surface swab cultures are NOT indicated for pressure ulcer diagnosis because all pressure ulcer surfaces are colonized with bacteria, making swabs unable to differentiate colonization from true infection 4
• Correlations between swabs, aspiration, and deep-tissue biopsy culture results have been poor 4

When Deep Tissue Cultures ARE Indicated

• Only obtain deep specimens for culture (tissue and bone at surgical debridement or biopsy) if the pressure ulcer demonstrates poor healing and/or persistent purulent drainage 4
• Deep-tissue biopsy or needle aspiration (performed only by skilled physicians) is appropriate when unusual pathogens are suspected, fluctuant areas suggest abscess, or initial antimicrobial treatment has failed 4

Imaging for Osteomyelitis Evaluation

• MRI is the most sensitive (98%) and specific (89%) imaging modality to detect osteomyelitis in pressure ulcers 4
• Bone biopsy for histopathologic examination definitively confirms osteomyelitis diagnosis and is most useful for guiding antimicrobial therapy 4
• Note that positive probe-to-bone testing and exposed bone with positive swab cultures do NOT diagnose osteomyelitis in pressure ulcers 4

Nutritional Intervention Based on Laboratory Results

For Malnourished Patients (Low Albumin/Prealbumin)

• Provide oral nutritional supplementation specifically enriched with arginine, zinc, and antioxidants rather than standard formulas 1
• These specialized formulations (14g arginine, 14g glutamine, 2.4g calcium β-HMB daily) showed significant improvement with 43% tissue improvement versus 26% in controls 1

Key Laboratory Limitations

• Although serum albumin, prealbumin, transferrin, and anthropometric measures may establish overall prognosis, they do not precisely represent nutritional status 2
• No single laboratory test can exactly define an individual's nutritional status 2
• Despite these limitations, these markers guide supplementation decisions in clinical practice 1, 2

Clinical Infection Diagnosis

• Diagnosis of pressure ulcer infection requires clinical criteria, not laboratory values alone 4, 6
• Clinical signs include purulent discharge plus 4 of the following: fever (≥38°C), worsening mental or functional status, warmth, redness, swelling, localized tenderness/pain, or serous drainage 4
• Use NERDS-STONEES criteria to differentiate critical colonization from deep tissue infection 6