What are the causes of elevated procalcitonin levels in a postpartum woman after a Lower Segment Caesarean Section (LSCS)?

Elevated Procalcitonin Post-LSCS: Causes and Clinical Approach

Elevated procalcitonin after Lower Segment Caesarean Section most commonly indicates postoperative bacterial infection, particularly surgical site infection or endometritis, though physiologic postpartum elevation up to 0.25 μg/L is normal and should not trigger antibiotic therapy.

Normal Postpartum PCT Reference Values

Understanding baseline postpartum PCT levels is critical to avoid unnecessary antibiotic exposure:

• Third trimester baseline: 0.061 μg/L (range 0.010-0.110) 1
• At delivery: 0.068 μg/L (range 0.010-0.170) 1
• Days 2-3 postpartum: 0.200 μg/L (range 0.030-5.00), with approximately 8% of healthy women reaching 0.25-0.5 μg/L 1
• Day 10 postpartum: Returns to 0.060 μg/L (range 0.020-0.120) 1

A cut-off PCT level of 0.25 μg/L can be used during the third trimester, at delivery, and immediate postpartum period to rule out infection 1. Values below this threshold in an otherwise well-appearing patient do not warrant antibiotic initiation.

Primary Infectious Causes Post-LSCS

Surgical Site Infection (SSI)

The most common cause of significant PCT elevation after cesarean section:

• Incidence: 10.3 per 100 LSCS procedures, with superficial SSI comprising 66.7% of cases 2
• Microbiology: Gram-negative organisms predominate (55.3%), followed by gram-positive organisms (44.7%) 2
• Risk factors significantly associated with SSI post-LSCS:
  • Inappropriate pre-surgical antibiotic prophylaxis 2
  • Anemia 2
  • Previous LSCS as indication for current surgery 2
  • Intra-operative blood transfusion 2
  • Comorbid illness (heart disease, hypothyroidism, chronic liver/kidney disease) 2

Endometritis and Pelvic Infections

• PCT rises within 4-6 hours of bacterial invasion and peaks at 6-8 hours 3, 4
• Particularly suspect when PCT >0.5 μg/L with fever, uterine tenderness, or purulent lochia 3

Severe Systemic Bacterial Infections

• PCT 0.5-2.0 ng/mL: Systemic inflammatory response syndrome 3
• PCT 2.0-10 ng/mL: Severe sepsis 3
• PCT >10 ng/mL: Septic shock 3

Urinary Tract Infection/Pyelonephritis

• Common postpartum complication that elevates PCT when systemic 3

Non-Infectious Causes of PCT Elevation Post-LSCS

Physiologic Postpartum Elevation

• Normal transient rise to 0.200 μg/L at days 2-3 postpartum without infection 1
• This represents tissue trauma from surgery and delivery, not infection 1

Acute Respiratory Distress Syndrome (ARDS)

• Can falsely elevate PCT without bacterial infection 5, 3
• Particularly relevant if postpartum complications include aspiration or fluid overload

Chemical Pneumonitis

• May falsely elevate PCT levels 5, 3

Severe Viral Co-Infections

• Influenza or other severe viral illnesses can elevate PCT despite absence of bacterial co-infection 5, 3
• COVID-19 hyperinflammatory states may result in higher PCT production than other viral pneumonias 5, 3

Clinical Algorithm for Elevated PCT Post-LSCS

Step 1: Determine PCT Level and Timing

• PCT <0.25 μg/L: Infection unlikely; observe clinically 1
• PCT 0.25-0.5 μg/L: Possible infection; assess clinical context 3, 1
• PCT >0.5 μg/L: Bacterial infection likely; initiate workup 3
• PCT ≥1.5 ng/mL: Sepsis highly likely (100% sensitivity, 72% specificity); immediate intervention required 3

Step 2: Clinical Assessment

Examine specifically for:

• Wound examination: Erythema, warmth, purulent drainage, dehiscence 2
• Uterine tenderness and lochia characteristics (purulent, foul-smelling)
• Fever >38°C or hypothermia <36°C 3
• Hemodynamic instability: Tachycardia, hypotension suggesting sepsis 3
• Respiratory symptoms: Cough, dyspnea, hypoxia 5

Step 3: Diagnostic Workup (if PCT >0.5 μg/L)

• Blood cultures: At least two sets before antibiotics 6
• Complete blood count with differential 5
• Wound culture if SSI suspected 2
• Urinalysis and urine culture 6
• Chest imaging if respiratory symptoms present 6
• Serial PCT measurements: More valuable than single reading; 50% rise indicates worsening infection, >25% decrease indicates treatment response 3, 7

Step 4: Antibiotic Decision-Making

For PCT >0.5 μg/L with clinical signs of infection:

• Initiate empiric broad-spectrum antibiotics immediately targeting gram-negative and gram-positive organisms 6, 2
• Piperacillin-tazobactam or carbapenem depending on local resistance patterns 6
• Do not delay antibiotics while awaiting culture results if sepsis suspected 6

For PCT 0.25-0.5 μg/L:

• If clinically well-appearing with normal vital signs: Observe with serial PCT measurements 3, 1
• If any clinical concern: Treat as above 3

Critical Pitfalls to Avoid

• Do not treat physiologic postpartum PCT elevation (0.2-0.25 μg/L) with antibiotics in well-appearing patients 1
• Early sampling (<6 hours from symptom onset) may produce false-negative results as PCT requires 2-3 hours to rise and 6-8 hours to peak 3, 7
• Do not use PCT as sole marker; always integrate with clinical assessment 5, 3
• Renal dysfunction affects PCT clearance, potentially causing falsely elevated levels 3
• Serial measurements are superior to single values for guiding antibiotic duration and detecting treatment failure 3, 7, 6

Monitoring and De-escalation

• Repeat PCT daily once elevated 3, 6
• >25% decrease from peak: Indicates effective treatment response 3
• 50% increase from previous value: Indicates worsening infection requiring escalation 3
• Consider antibiotic de-escalation when PCT decreases significantly alongside clinical improvement 6
• Close monitoring for 72 hours postpartum is recommended for all LSCS patients, particularly those with risk factors 5