Leukocytosis (Raised WBC) in a Diabetic Patient

Why WBC Rises in a Diabetic Patient - Causes

A. NON-INFECTIOUS (Metabolic/Stress)

Goldman-Cecil Medicine notes: "Many cases are due to noninfectious causes, including inflammatory conditions (renal insufficiency, diabetic ketoacidosis, lupus erythematosus), and demargination stress reactions (dehydration, systemic corticosteroids)." Check for toxic granulations, Dohle bodies, and a band-cell shift on the peripheral smear to differentiate.

B. INFECTIOUS CAUSES (Most Common & Clinically Important)

1. Diabetic Foot Infection / Osteomyelitis

• Most common cause in a diabetic with leukocytosis
• Microangiopathy + neuropathy (motor, sensory, autonomic) leads to ulcers, soft-tissue infection, and bone invasion
• Organisms: polymicrobial - S. aureus most common, followed by S. epidermidis; moderate/severe infections also involve gram-negatives, anaerobes, MRSA
• WBC >12,000/mm³ with >10% bands = part of the SIRS/IWGDF severity classification (Grade 4/Severe)

2. Urinary Tract Infections (UTI) - Including Emphysematous Pyelonephritis

• Diabetes is a risk factor for complicated UTIs
• Emphysematous pyelonephritis (gas-forming, necrotizing renal infection) - almost exclusively in diabetics - is a urologic emergency presenting with sepsis and leukocytosis
• Other diabetes-specific UTI syndromes: renal/perinephric abscess, papillary necrosis, xanthogranulomatous pyelonephritis

3. Cellulitis / Skin & Soft Tissue Infections

• Manifests as erythema, warmth, edema, tenderness + fever + leukocytosis
• Diabetics have impaired skin barrier and immune response

4. Necrotizing Soft Tissue Infections (NSTI) / Necrotizing Fasciitis

• Rapidly spreading infection along fascial planes
• Diabetes is a major risk factor
• Presents with disproportionate pain, crepitus, systemic sepsis, and marked leukocytosis
• This is a surgical emergency

5. Rhinocerebral Mucormycosis

• Seen in ~70% of cases in diabetic patients (especially poorly controlled/DKA)
• Presents with facial pain, nasal discharge (black eschar), proptosis, headache - cranial nerve palsies
• Leukocytosis reflects the invasive fungal infection

6. Other Infections

• Liver abscess (diabetes + biliary disease)
• Deep neck space infections
• Pneumonia

Approach to Diagnosis

Step 1 - Clinical Assessment

• History: fever, localizing symptoms (foot ulcer, dysuria, facial pain, skin changes)
• Examination: vital signs for SIRS (temp >38 or <36°C, HR >90, RR >20, WBC >12,000)
• Peripheral blood smear: look for toxic granulations, Dohle bodies, band cells (left shift confirms infection, not just stress demargination)

Step 2 - Investigations by Suspected Site

Investigation of Choice

• Diabetic foot osteomyelitis: MRI foot - recommended by the American College of Radiology (appropriateness criteria score 9/9); detects changes earlier than X-ray
• Emphysematous pyelonephritis: CT abdomen (gas within renal parenchyma)
• Rhinocerebral mucormycosis: MRI brain + sinuses
• Sepsis source unknown: Blood cultures + procalcitonin

Diabetic Foot Osteomyelitis: cortical bone destruction at the 5th metatarsal head and adjacent phalanx with overlying soft tissue swelling - Grainger & Allison's Diagnostic Radiology

Treatment

1. Glycaemic Control (Always First)

• Optimise blood glucose - hyperglycaemia impairs neutrophil function and wound healing
• Insulin is the agent of choice in inpatient/acute settings

2. Diabetic Foot Infection - Antibiotic Therapy (IWGDF/IDSA 2023 Guidelines)

3. Surgical Management

• Diabetic foot: Debridement, drainage of abscess; amputation for severe/non-salvageable limb
• Necrotizing fasciitis: Emergency surgical debridement (surgery + antibiotics - no role for antibiotics alone)
• Emphysematous pyelonephritis: Fluid resuscitation + glucose control + antibiotics + percutaneous nephrostomy or nephrectomy

4. Rhinocerebral Mucormycosis

• Reverse predisposing factor (control DKA, stop steroids)
• Liposomal Amphotericin B - antifungal of choice
• Aggressive surgical debridement of necrotic tissue
• Often fatal if treatment is delayed

5. If Non-Infectious (DKA/HHS)

• Treat the underlying DKA/HHS (IV fluids, insulin, electrolyte correction)
• Leukocytosis resolves as metabolic state corrects
• Empirical antibiotics are not routinely indicated unless infection cannot be excluded clinically

Summary Table

Functions of White Blood Cells (Leukocytes)

"The real value of WBCs is that most of them are specifically transported to areas of serious infection and inflammation, thereby providing a rapid and potent defense against infectious agents." - Guyton & Hall Medical Physiology

The 5 Types and Their Specific Functions

1. Neutrophils (50-70% of all WBCs)

• Chemotaxis - they detect chemical signals (bacterial toxins, complement fragments, clotting products) released at sites of infection and migrate toward them, guided by a concentration gradient, up to 100 µm away from the source
• Diapedesis - they squeeze through gaps between capillary endothelial cells to reach infected tissues
• Phagocytosis - they engulf bacteria by extending pseudopodia around them, forming a phagosome; lysosomes then fuse with the phagosome to form a phagolysosome, releasing digestive enzymes (lysozyme, lactoferrin, myeloperoxidase) that kill the organism
• Each neutrophil can phagocytize 3-20 bacteria before it dies
• Their granules contain antimicrobial peptides and enzymes ready for immediate killing

Neutrophils undergoing margination, diapedesis, and chemotaxis toward an infected tissue site - Guyton & Hall

2. Monocytes → Macrophages (2-8% of WBCs)

• In the blood they are immature (monocytes) with limited killing ability
• Once they enter tissues, they swell up to 5x in diameter (60-80 µm) and become macrophages - extremely potent defenders
• Macrophages can phagocytize particles up to 100x larger than neutrophils can handle, including whole red blood cells, parasites, and even dead neutrophils
• They also present antigens to T lymphocytes, linking innate and adaptive immunity
• Tissue macrophages can live for months
• They release cytokines (TNF, IL-1, IL-6) that orchestrate the inflammatory response

3. Lymphocytes (20-40% of WBCs)

• Lymphocytes continuously recirculate - from blood → tissues → lymph → back to blood
• They form immunological memory (reason vaccines work)
• Life span: weeks to months (memory cells can last years)

4. Eosinophils (1-4% of WBCs)

• Their specific granules contain cytotoxic proteins that are toxic to helminths (worms) and protozoa
• They play a key role in allergic reactions and chronic inflammation
• Elevated in: asthma, hay fever, drug reactions, parasitic infections (mnemonic: NAACP - Neoplasm, Allergy, Asthma, Collagen vascular disease, Parasites)

5. Basophils (<0.5% of WBCs)

• Their large granules contain: histamine, heparin, heparan sulfate, leukotrienes
• Release of these substances causes the classic signs of allergy: vasodilation, increased capillary permeability, bronchospasm
• Functionally similar to mast cells (their tissue counterparts)
• Heparin they release prevents blood from clotting in inflamed areas, allowing better immune cell circulation

How WBCs Work Together - A Summary

INFECTION / FOREIGN SUBSTANCE DETECTED
           ↓
Neutrophils → arrive first (minutes to hours) → phagocytose bacteria
           ↓
Monocytes → arrive later → become macrophages → powerful phagocytosis
           ↓
Macrophages → present antigens to T lymphocytes
           ↓
T cells (helper) → activate B cells
           ↓
B cells → produce antibodies → opsonise pathogens
           ↓
Opsonised pathogens → phagocytosed more efficiently (opsonisation)
           ↓
Memory cells formed → faster response on next exposure

Normal WBC Reference Values

In Short