CBC Indices and Serum Lactate in Neonatal Sepsis

Neonatal sepsis remains one of the most devastating conditions encountered in neonatal intensive care units (NICUs) worldwide. The global population-level incidence of neonatal sepsis is estimated at approximately 2,202 cases per 100,000 live births, with mortality ranging between 11% and 19%. Diagnosis is clinically challenging because signs are nonspecific and overlap with other neonatal conditions. Although blood culture is the gold standard for diagnosis, it has significant limitations, including a 48 to 72-hour delay for results, low sensitivity due to the small blood volumes collected from neonates, and the risk of contamination. Complete blood count (CBC) indices, including the absolute neutrophil count, immature-to-total neutrophil (I/T) ratio, mean platelet volume (MPV), and red cell distribution width (RDW), have attracted interest as accessible screening tools. Furthermore, serum lactate is an established critical prognostic biomarker that reflects tissue hypoperfusion and anaerobic metabolism. This study aims to evaluate the combined diagnostic and prognostic values of these CBC-derived indices and serum lactate in a resource-limited NICU environment.

Upon admission to the NICU, every enrolled neonate will undergo a comprehensive clinical assessment.

• Maternal and perinatal history will be extracted from obstetric records, including details such as maternal age, duration of premature rupture of membranes (PROM), intrapartum fever, maternal urinary tract infections, Group B Streptococcus (GBS) status, and mode of delivery.
• Continuous physiologic monitoring will record heart rate, respiratory rate, and oxygen saturation.
• Core body temperature will be assessed continuously using skin temperature probes.
• An attending neonatologist will conduct a physical examination to document clinical signs of sepsis, including feeding intolerance, abdominal distension, lethargy, hypotonia, apnea, chest retractions, cyanosis, and altered capillary refill time.

To prevent pre-analytical errors and sample contamination, a strict aseptic blood sampling protocol will be executed prior to the administration of any empirical antimicrobial therapy.

• Skin antisepsis will be performed using a two-step technique with 70% isopropyl alcohol followed by 2% chlorhexidine gluconate, which will be allowed to air-dry completely.
• A precise volume of 3.0 to 4.0 mL of peripheral venous blood will be extracted.
• The blood will be distributed in a strict order of draw: 1.0 to 2.0 mL for the pediatric aerobic blood culture bottle, 1.0 mL into a gray-top tube containing Sodium Fluoride and Potassium Oxalate to halt glycolysis for lactate testing, and 1.0 mL into a purple-top K2EDTA tube for the CBC.

Laboratory Analytical Methods:

• CBC parameters will be analyzed using a fully automated, 5-part differential hematology analyzer utilizing flow cytometry and electrical impedance (Coulter principle). Additionally, a manual peripheral blood smear stained with Leishman's stain will be evaluated under a light microscope by a designated clinical pathologist blinded to the patient's clinical status. The pathologist will evaluate for toxic granulation, Döhle bodies, and cytoplasmic vacuolization, and perform a manual 100-cell differential count to calculate the I/T ratio.
• Serum lactate levels will be quantified using a high-throughput automated clinical chemistry analyzer, with photometric measurement at a wavelength of 540 to 550 nm.
• Blood cultures will be loaded into an automated, continuous-monitoring microbial detection system. Bottles will be incubated at 37.0°C and continuously agitated, utilizing sensors to detect carbon dioxide produced by actively metabolizing microorganisms. Negative bottles will be incubated for a full 5 days before being finalized.

Inclusion criteria

• Neonates aged 0 to 28 days (term and preterm).
• Presence of two or more clinical signs highly suggestive of sepsis (e.g., temperature instability [< 36.5°C or > 37.5°C], tachycardia/bradycardia, tachypnea, feeding intolerance, lethargy, or altered muscle tone).
• Informed written consent obtained from the parents or legal guardians.

Exclusion criteria

• Neonates with severe congenital anomalies or chromosomal abnormalities.
• Neonates diagnosed with Inborn Errors of Metabolism (which inherently alter lactate levels).
• Neonates with severe perinatal asphyxia or Hypoxic-Ischemic Encephalopathy (HIE), as these conditions cause profound primary lactic acidosis independent of sepsis.
• Neonates who received prior broad-spectrum intravenous antibiotics for more than 24 hours prior to admission.
• Neonates who have received prior blood transfusions.
• Neonates requiring immediate surgical intervention.