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Neonatal Sepsis Workup

  • Author: Ann L Anderson-Berry, MD, PhD; Chief Editor: Ted Rosenkrantz, MD  more...
 
Updated: Dec 31, 2015
 

Approach Considerations

Laboratory studies used to evaluate for early-onset and late-onset sepsis include a complete blood count (CBC) and differential, blood and cerebrospinal fluid (CSF) cultures, and measurement of levels of C-reactive protein (CRP) and possibly other infection markers.[18] In some cases, serial CBC and CRP studies may be appropriate. A Gram stain provides early identification of the gram-negative or gram-positive status of the organism for preliminary identification.

Because of the low incidence of meningitis in the newborn with negative blood culture results, clinicians may elect to culture the CSF of only those infants with documented or presumed sepsis. However, data from large studies show a 38% rate of culture-positive meningitis in neonates with negative blood culture results and suspected sepsis. Accordingly, a lumbar puncture should be part of the evaluation of an infant with suspected sepsis.

Emerging technology using polymerase chain reaction (PCR), though not yet available clinically, could eventually help achieve faster identification of sepsis and the causative organism than can be achieved with blood culture alone.[19] Rapid pathogen detection with multiplex PCR may facilitate more timely selection of targeted antibiotic therapy while limiting exposure to broad-spectrum antibiotics.[20]

Imaging studies employed in the workup of neonatal sepsis may include chest radiography to evaluate pulmonary involvement, as well as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonography of the head in cases of meningitis.

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Laboratory Studies

Cultures

Aerobic and anaerobic cultures are appropriate for most of the bacterial pathogens associated with neonatal sepsis. Anaerobic cultures are especially important in neonates who have abscesses, processes with bowel involvement, massive hemolysis, or refractory pneumonia.

Bacterial culture results should generally reveal the organism of infection within 36-48 hours; subsequent initial identification of the organism occurs within 12-24 hours of the growth. Single-site blood cultures are effective for isolating bacteria in neonates with sepsis.[21] Urine cultures are most appropriate for the investigation of late-onset sepsis.

Complete blood count and differential

A CBC and differential may be ordered serially to determine changes associated with the infection (eg, thrombocytopenia or neutropenia) or to monitor the development of a left shift or changes in the ratio of immature to total neutrophils. Such serial monitoring of the CBC may be useful in aiding the differentiation of sepsis from nonspecific abnormalities due to the stress of delivery.

Platelet count

The platelet count in the healthy newborn is rarely lower than 100,000/µL in the first 10 days of life (normal, ≥150,000/μL). Thrombocytopenia (platelet counts < 100,000/µL) may be a presenting sign of neonatal sepsis and can last as long as 3 weeks; 10-60% of infants with sepsis have thrombocytopenia.[22]

Because of the appearance of newly formed platelets, mean platelet volume (MPV) and platelet distribution width (PDW) are significantly higher in neonatal sepsis after 2-3 days of life. These measures may assist in determining the cause of thrombocytopenia. However, because of the myriad of causes of thrombocytopenia and its late appearance in neonatal sepsis, the presence of thrombocytopenia generally does not aid the diagnosis of neonatal sepsis.

White blood cell counts and ratios

Although white blood cell (WBC) counts and ratios are more sensitive for determining sepsis than platelet counts are, they remain very nonspecific and have a low positive predictive value. Normal WBC counts may be initially observed in as many as 50% of cases of culture-proven sepsis. Infants who are not infected may also demonstrate abnormal WBC counts related to the stress of delivery or to any of several other factors.

A differential may be of use in diagnosing sepsis; however, these counts are largely dependent on the laboratory technician performing them. The total neutrophil count (polymorphonuclear cells [PMNs] and immature forms) is slightly more sensitive for determining sepsis than the total leukocyte count (percent lymphocyte + monocyte/PMNs + bands).

Abnormal neutrophil counts at the time of symptom onset are observed in only two thirds of infants; therefore, the neutrophil count does not provide adequate confirmation of sepsis. Neutropenia is also observed with maternal hypertension, severe perinatal asphyxia, and periventricular or intraventricular hemorrhage.

Neutrophil ratios have been more useful in diagnosing neonatal sepsis; of these, the immature-to-total (I/T) ratio is the most sensitive (60-90%). All immature neutrophil forms are counted. The maximum acceptable I/T ratio for excluding sepsis in the first 24 hours is 0.16. In most newborns, the ratio falls to 0.12 within 60 hours of birth. Because elevated I/T ratios may be observed with other physiologic events, their positive predictive value is limited; thus, in the diagnosis of sepsis, an elevated I/T ratio should be used in combination with other signs.

C-reactive protein Procalcitonin and other markers

levels of CRP, an acute-phase protein associated with tissue injury, are elevated at some point in 50-90% of infants with systemic bacterial infections.[23] CRP levels rise secondary to macrophage, T-cell, and adipocyte production of interleukin (IL)–6. This is especially true of infections with abscesses or cellulitis of deep tissue.

CRP levels usually begin to rise within 4-6 hours of the onset of infection, become abnormal within 24 hours of infection, peak within 2-3 days, and remain elevated until the inflammation is resolved. The CRP level is not recommended as a sole indicator of neonatal sepsis but may be used as part of a sepsis workup or as a serial study during infection to assess the response to antibiotics, determine the duration of therapy, or identify a relapse of infection.

Immunoglobulin M (IgM) concentration in serum may be helpful in determining the presence of an intrauterine infection, especially if the infection has been present for some time. Elevated IgM levels in umbilical cord serum suggest intrauterine infection.

Evidence on the use of infection markers such as CD11b, CD64, IL-6, and IL-8 for evaluation of sepsis in neonates shows that they may be helpful as adjunctive markers.[24] Their value may be further enhanced by performing serial measurements and using combinations of tests. At present, however, the consensus is that these tests should not be used alone to determine the need for antibiotic therapy, though in some cases they may prove useful in determining when to stop antibiotic therapy.

Levels of other acute-phase reactants (eg, procalcitonin and serum amyloid) are often elevated with the onset of sepsis. Procalcitonin, a propeptide of calcitonin produced in monocytes and in the liver, may be more sensitive than CRP. It is more specific to bacterial infection than viral infection and has been shown to be useful after age 24 hours in neonates with suspected bacterial sepsis. It can be elevated in infants with respiratory distress syndrome and in infants of diabetic mothers, and it should be used in conjunction with the entire clinical situation and not as a single determinant of treatment. Evidence of usefulness of procalcitonin in the neonate is mounting, and rapid turnaround times (90-120 min) are proving increasingly useful in a clinical setting. Procalcitonin may be used in combination with other acute-phase reactants, such as CRP.[8, 25, 26]

Coagulation studies

Disseminated intravascular coagulation (DIC) can occur in infected infants. Predicting which infants will be affected at the onset of sepsis is difficult.[27]

Infants with DIC show abnormalities in the prothrombin time (PT), the partial thromboplastin time (PTT), and fibrinogen and D-dimer levels, and they may need blood products, including fresh frozen plasma (FFP) and cryoprecipitate, to replace coagulation factors consumed in association with DIC. If infants show signs consistent with impaired coagulation (eg, gastric blood, bleeding from intravenous [IV] or laboratory puncture sites, or other bleeding), coagulation should be evaluated by checking these values.

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Lumbar Puncture and CSF Analysis

Lumbar puncture is warranted for early- and late-onset sepsis, though clinicians may be unsuccessful in obtaining sufficient or clear fluid for all the studies. Infants may be positioned on their side or in a sitting position with support. The insertion site should be between L3 and L4 to ensure that it is below the lowest point of the spinal cord in infants.

If positive culture results are obtained, a follow-up lumbar puncture is often performed within 24-36 hours after initiation of antibiotic therapy to document CSF sterility. If organisms are still present, modification of the drug type or dosage may be required for adequate treatment of the meningitis. An additional lumbar puncture within 24-36 hours of the change in therapy is necessary if organisms are still present.

CSF analysis

CSF findings in infective neonatal meningitis are as follows:

  • Elevated WBC count (predominantly PMNs)
  • Elevated protein level
  • Decreased glucose concentration
  • Positive culture results

The CSF WBC count is within the reference range in 29% of group B Streptococcus (GBS) meningitis infections but in only 4% of gram-negative meningitis infections. Reference-range CSF protein and glucose concentrations are found in about 50% of patients with GBS meningitis but in only 15-20% of patients with gram-negative meningitis. CSF culture is critical, in that neonatal meningitis often occurs in patients without bacteremia and with normal CSF findings.[28]

The decrease in CSF glucose concentration does not necessarily reflect serum hypoglycemia. Glucose concentration abnormalities are more severe in late-onset disease and with gram-negative infections.

Herpes simplex virus PCR testing

No consensus has been reached regarding the inclusion of herpes simplex virus (HSV) PCR testing of CSF as part of a routine sepsis workup in the neonate. Currently, HSV PCR is reserved for infants with CNS abnormalities, skin vesicles, and CSF abnormalities or for infants who have clinical symptoms but have negative cultures and do not respond to antibiotics.[29] However, vesicles are not present in as many as one third of CNS HSV and disseminated HSV cases. Further research in this area is needed to provide clear practice recommendations.

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Radiography, CT, MRI, and Ultrasonography

Chest radiography may reveal segmental or lobar infiltrate but more commonly reveals a diffuse, fine, reticulogranular pattern, much like that seen in respiratory distress syndrome (RDS). Pleural effusions may also be observed.

CT scanning or MRI may be needed late in the course of complex neonatal meningitis to document obstructive hydrocephalus, the site where the obstruction is occurring, and the occurrence of major infarctions or abscesses. Signs of chronic disease (eg, ventricular dilation, multicystic encephalomalacia, and atrophy) may also be demonstrated on CT scanning or MRI.

Head ultrasonography in neonates with meningitis may reveal evidence of ventriculitis, abnormal parenchymal echogenicities, extracellular fluid, and chronic changes. Serially, head ultrasonography can reveal the progression of complications.

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Contributor Information and Disclosures
Author

Ann L Anderson-Berry, MD, PhD Associate Professor of Pediatrics, Section of Newborn Medicine, University of Nebraska Medical Center, Creighton University School of Medicine; Medical Director, NICU, Nebraska Medical Center

Ann L Anderson-Berry, MD, PhD is a member of the following medical societies: American Academy of Pediatrics, Nebraska Medical Association, Society for Pediatric Research

Disclosure: Nothing to disclose.

Coauthor(s)

Linda L Bellig, MA, RN NNP, (Retired) Track Coordinator, Instructor, Neonatal Nurse Practitioner Program, Medical University of South Carolina College of Nursing

Disclosure: Nothing to disclose.

Bryan L Ohning, MD, PhD Medical Director of NICU, Medical Director of Neonatal Transport, Division of Neonatology, Children's Hospital, Greenville Hospital System, University Medical Center; GHS Professor of Clinical Pediatrics, University of South Carolina School of Medicine; Clinical Associate Professor of Pediatrics, Medical University of South Carolina

Bryan L Ohning, MD, PhD is a member of the following medical societies: American Academy of Pediatrics, American Thoracic Society, South Carolina Medical Association

Disclosure: Received salary from Pediatrix Medical Group of SC for employment.

Chief Editor

Ted Rosenkrantz, MD Professor, Departments of Pediatrics and Obstetrics/Gynecology, Division of Neonatal-Perinatal Medicine, University of Connecticut School of Medicine

Ted Rosenkrantz, MD is a member of the following medical societies: American Academy of Pediatrics, American Pediatric Society, Eastern Society for Pediatric Research, American Medical Association, Connecticut State Medical Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

Acknowledgements

David A Clark, MD Chairman, Professor, Department of Pediatrics, Albany Medical College

David A Clark, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Pediatric Society, Christian Medical & Dental Society, Medical Society of the State of New York, New York Academy of Sciences, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Scott S MacGilvray, MD Clinical Professor, Department of Pediatrics, Division of Neonatology, The Brody School of Medicine at East Carolina University

Scott S MacGilvray, MD is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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