Dear Editor,

We appreciate the comments by Dr. Thayyil et al. As we do not agree with their objections we would like to point out the following aspects of this study: This study is focused on preterm infants. Neonates and in particular preterm infants have been shown to display differences in various immune functions. Little is known about circulating levels of LBP in neonates. Therefore we have indeed included term newborns to compare data of preterm infants.

It would be advantageous to include larger gestational age groups which were unavailable in this first study on LBP levels. Here we decided to evaluate combined subgroups on the basis of the limited total number of study infants. This also reduces potential confounders, e.g. labour. The exclusion criteria applied do not cause bias. We also would like to draw attention to the fact that CRP cut off in this study is 5 mg/L and not, as erroneously interpreted by Thayill et al., 5 mg/dl. Recent studies using high laboratory sensitivity techniques with a CRP detection rate of > 0,2 mg/l, showed that in the absence of bacterial infection neonatal CRP levels are far below 5 mg/l [1,2]. The rate of positive blood cultures in our institution has fluctuated in recent years due to high percentage of antibiotic use in pregnant women. However, LBP values of the two infants with positive blood cultures were very close to median values at any time of measurement. We did not culture any other body fluids. Correlation of inflammatory markers with bacterial colonization may involve pathogenic, clinically relevant, as well as non- pathogenic, clinically not relevant pathogens. A potential key to a solution of this dilemma could be to correlate the presence of genomic DNA with biochemical and physiological inflammatory responses [3].

This study has a clear result: LBP is not an early parameter for NBI, it is not influenced by labour or prematurity. Nevertheless, its value for the diagnostic routine of infectious disease needs to be determined.

References

1) Dembinski J, Behrendt D, Schlebusch H and Bartmann P. C-Reactive Protein (CRP) In Cord Blodd: Is "Negative" CRP Negative? 5th World Congress on Trauma, Shock, Inflammation and Sepsis. 2000 by Mundozzi Editore, Italy-Medimond, USA.

2) Wasunna A, Whitelaw A, Gallimore R, Hawkins PN and Pepys MB. C-reactive protein and bacterial infection in preterm infants. Eur J Pediatr (1990) 149:424-427.

3) Evaluation of a real-time fluorescent PCR assay for rapid detection of Group B Streptococci in neonatal blood. Diagn Microbiol Infect Dis. 2004 Sep;50(1):7-13.

4) Ehl S, Gehring B and Pohlandt F. A detailed analysis of changes in C- reactive protein levels in neonates treated for bacterial infection. Eur J Pediatr (1999) 158: 238-242.

Dear Editor,

Congratulations to Behrendt and team for introducing yet another infection marker in premature babies [1]. However, there are several flaws in the study design which could render the study conclusions not clinically useful.

The authors repeatedly mention the aim of their study was to look at lipopolysaccharide binding protein (LBP) levels in premature babies. Results quoted however include data on term infants (23%) and appear to have combined data for preterm and term infants. Authors have also excluded 26% of the eligible population introducing further potential bias.

The authors consider one of the gold standards for diagnosing neonatal bacterial infection as at least 3 clinical symptoms from a detailed list and a CRP of > 5mg/dl. The majority of newborns with mild respiratory distress syndrome or transient tachypnea would have all of these symptoms and could have a CRP of 5-10mg/dl. The use of CRP in the diagnosis of neonatal bacterial infection is a controversial area. Most studies have reported positive likelihood ratios of CRP in diagnosing bacterial infection in the range of 1-4 and negative likelihood ratios 0.5 -1, showing limited clinical utility [2]. Do the authors have any data from their population showing likelihood ratios of CRP for diagnosis of bacterial infection, to substantiate their claim that a CRP > 5 mg/dl indicates bacterial infection? Many studies have actually taken CRP < 10 mg/dl as normal [2-4]. What proportion of the infants fell within this uncertain 5-10mg/dL group?

The second criterion for gold standard is a positive blood culture and at least 3 clinical symptoms. This would exclude a baby with apnoea, whose blood culture has grown a pathogenic organism. Authors do not mention if they have cultured any other body fluids (urine or CSF). It would be interesting to know what the LBP levels were in the 2 babies with a positive blood culture. The test would be much more usefully evaluated in a cohort of babies with positive cultures, since these at least would have harder evidence of infection. The blood culture positivity rate in the study was low (2 positives in 74 babies = 2.7%)

The authors’ initial hypothesis was that LBP might fill the diagnostic gap between IL-6 and CRP. Unfortunately the time to maximum median value of LBP falls outside of this critical period. Despite this the authors conclude LBP may be useful diagnostic marker of infection in premature babies. It is not clear why, as infants with risk factors will already have been started on antibiotics by this time. Did the authors look at tests for diagnostic utility of LBP (e.g. sensitivities, likelihood ratios) to support this claim. Larger studies using more a stringent gold standard comparing LBP with traditional markers [5] for diagnostic accuracy of neonatal bacterial infection will be needed before LBP becomes routine neonatal practice.

References

(1). Behrendt D, Dembinski J, Heep A, Bartmann P. Lipopolysaccharide binding protein in preterm infants. Arch Dis Child 2004; 89: F551-F554

(2). Fowlie PW, Schmidt B. Diagnostic tests for bacterial infection from birth to 90 days: a systematic review. Arch Dis Child.1998;78:F92-F98

(3). Laborada G, Rego M, Jain A, Guliano M, Stavola J, Ballabh P, Krauss AN, Auld PA, Nesin M. Diagnostic value of cytokines and C-reactive protein in the first 24 hours of neonatal sepsis. Am J Perinatol. 2003;20(8):491-501

(4). Franz AR, Kron M, Pohlandt F, Steinbach G Comparison of procalcitonin with interleukin 8, C-reactive protein and differential white blood cell count for the early diagnosis of bacterial infections in newborn infants. Pediatr Infect Dis J. 1999;18(8):666-71.

(5). Pavcnik-Arnol M, Hojker S, Derganc M. Lipopolysaccharide-binding protein in critically ill neonates and children with suspected infection: comparison with procalcitonin, interleukin-6, and C-reactive protein. Intensive Care Med. 2004;30 (7):1454-60