Diagnostic approach to neonatal sepsis

Risk Factors - Sepsis Red Flags

• Maternal Factors (Perinatal):

  • Intrapartum fever >38°C (100.4°F)
  • Prolonged Rupture of Membranes (PROM) >18 hours
  • Chorioamnionitis
  • Maternal Group B Strep (GBS) colonization/infection
  • Preterm labor

• Neonatal Factors:

  • Prematurity (<37 weeks)
  • Low birth weight (<2.5 kg)
  • Invasive procedures (e.g., catheters, ventilation)

• Clinical Red Flags (Signs of Sepsis):

  • Temperature instability (fever or hypothermia)
  • Respiratory distress (grunting, tachypnea, retractions)
  • Poor feeding, vomiting
  • Lethargy, irritability, or hypotonia
  • Cardiovascular: Tachycardia, bradycardia, poor perfusion (CRT >3s)

⭐ High-Yield: Seizures can be the sole presenting sign of neonatal sepsis, particularly in GBS meningitis.

Clinical Clues - The Silent Signs

• General: Lethargy, poor cry, refusal to feed, hypotonia.
• Temperature Instability: Hypothermia (<36.5°C) is more common than fever (>38°C), especially in preterm infants.
• Respiratory: Apnea/gasps, tachypnea (>60/min), grunting, nasal flaring, chest retractions.
• Cardiovascular: Tachycardia (>160/min) or bradycardia (<100/min), prolonged CRT (>3s), hypotension (late sign).
• Neurologic: Irritability, seizures, altered sensorium, bulging fontanelle.
• Gastrointestinal: Abdominal distension, vomiting, feed intolerance.
• Cutaneous: Jaundice, petechiae, purpura, sclerema (a grave sign).

⭐ High-Yield: The most common signs of neonatal sepsis are subtle and non-specific. Hypothermia is a more frequent and ominous indicator than fever in neonates, particularly in preterm and low birth weight infants.

Lab Investigations - The Bug Hunt

• Sepsis Screen (Screening Tests)

  • Total Leucocyte Count (TLC): < 5000/mm³
  • Absolute Neutrophil Count (ANC): ↓ (Refer to Manroe/Mouzinho charts)
  • Immature/Total Neutrophil (I/T) Ratio: > 0.2
  • Micro-ESR: > 15 mm in 1st hour
  • C-Reactive Protein (CRP): > 10 mg/L; serial measurements are key (↑ trend).
  • 💡 Procalcitonin (PCT): More specific than CRP; rises earlier.

• Gold Standard (Definitive)

  • Blood Culture: 1-2 mL blood from a peripheral vein before antibiotics. The definitive diagnostic test.

• Supportive Investigations

  • CSF Analysis: If meningitis suspected (↑ cells, ↑ protein, ↓ sugar).
  • Chest X-ray: If respiratory distress is present.
  • Urine Culture: Especially for late-onset sepsis.

⭐ Exam Favourite: The I/T ratio > 0.2 is considered the most sensitive component of the neonatal sepsis screen.

Sepsis Screen - Scoring the Risk

A panel of rapid tests to stratify risk. A score of 1 is assigned to each positive parameter. A total score ≥ 2 is significant and suggests sepsis.

• Total Leucocyte Count (TLC): < 5000/mm³
• Absolute Neutrophil Count (ANC): Abnormal value (as per Manroe/Mouzinho charts)
• Immature/Total (I/T) Neutrophil Ratio: > 0.2
• C-Reactive Protein (CRP): Positive (> 10 mg/L)
• Micro-ESR: > 15 mm in the 1st hour

⭐ A negative sepsis screen (score < 2) has a high negative predictive value (>99%), making it excellent for ruling out sepsis.

High‑Yield Points - ⚡ Biggest Takeaways

• Blood culture is the gold standard, though often negative; always collect before antibiotics.
• The neonatal sepsis screen includes TLC, Absolute Neutrophil Count (ANC), I/T ratio, and CRP.
• An Immature-to-Total Neutrophil (I/T) ratio > 0.2 is the most sensitive and specific marker for early-onset sepsis.
• C-Reactive Protein (CRP) is the best marker for monitoring treatment response, but it rises late.
• Procalcitonin (PCT) rises earlier and is more specific for bacterial infection than CRP.
• Lumbar puncture is mandatory in all cases of late-onset sepsis.