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DIAGNOSTIC MARKERS OF INFECTION IN NEONATES. DR.ABED ALHALIM SHAMOUT. Introduction. Diagnostic markers of infection are useful indicators of n.sepsis. Serial measurements of these markers can improve diagnostic sensitivity,and the use of multiple markers can enhance diagnostic accuracy.
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DIAGNOSTIC MARKERS OFINFECTION IN NEONATES DR.ABED ALHALIM SHAMOUT
Introduction • Diagnostic markers of infection are useful indicators of n.sepsis. • Serial measurements of these markers can improve diagnostic sensitivity,and the use of multiple markers can enhance diagnostic accuracy. • Our aim is to improve the survival of newborn infants especially V.L.B.W.
Cont. • In n.sepsis in term and preterm infants,early warning signs and symptoms are often minimal,subtle,non-specific and can easily be misinterpreted as being due to non-infective causes ex:TTN, apnoea of prematurity,… • So infected infants must be identifed and differentiated from non-infected patients,and antibiotics started without delay.
The ideal diagnostic markers As most infection markers are essential mediators of inflammatory cascade,so they influenced by infective as well as non-infective iflammatory stimuli such as toxic and tissue damaging.
Characteristics of an ideal marker Clinical characteristics: 1.Awell defined optimal cut off that is comparable btw different NICU 2.favourable diagnostic utilities: A-sensitivity 100%(infected infants have apositive test) B-specificity(>85%)(the test is negative if no ifection)
Cont…. C-positive predictive value(>85%)(infection is present when the test is positive,to minimize unnecessary use of ABS in false + D-negative predictive value(100%)(negative test confidently rules out infection) 3.detects infection at an early stage 4.Differentiates between different types of pattogen 5-guides ABS use 6-prognostication
Labaratory characteristics 1.stable compound 2.adequate time window for specimen sampling (sustained for at least 48h after the onset of clincal manifestations) 3.quantitaive measurements. 4.small volume of specimen 5.easy method of measurement 6.quick lab turnover time. 7.low cost
Hematological tests 1.Total white blood cell count. 2.Total neutrophil count. 3.Immature neutrophil count. 4.Immature/total neutrophil ratio 5.Neutrophil morphology,vacuolisation,toxic granulation,intracellular bacteria
Cont.. • WBC and ratios varied widely across studies senst(17-90%) and specift(31-100%). • Normal WBC count observed in culture –proven sepsis in 50% of the cases. • Infants who are not infected may also have abnormal counts related to stress of delivery. • Total neut count (PMNS+Immature) is more sensitive in determining sepsis than WBC. • Abnormal neut count taken at time of onset are only obseved in 2/3 of the cases so it doent provide adequete confirmation of sepsis. • Neutropenia:maternal HTN,severe perinatal asphaxia severe IVH or periventricular hmg.
Cont… • So neatrophil ratio have been more useful in Dx or excluding n.sepsis; Immature to tatalratio is the most sensitive. • The max acceptable ratio for excluding sepsis during 1st 24hrs is 0.16 . Then it falls to 0.12 within 60days. Sensitivity ranged 60-90%.
Platelets • The plts count in healthy newborn is rarely less than 100,000 in the ist 10 days of life. • Thrombocytopeania<100,000 occurs in n.sepsis . • Thrombocytopenia is observed after sepsis has been Dx and usually lasts 1wk to 3wk. • MPV and PDW are shown to be signt higher after 3dys. • Because of wide DDx of thrombocytopenia in neonates and its late appearance, so it doesn’t aid so much in the Dx of N.sepseis.
Granulocyte colony stimulating factor G-CSF • Its amediator produced by BM it helps in proliferation and diff of neutrophils ,has been proposed to be areliable infection marker for early Dx of n.sepsis. • Cut off 200pg/ml, senst 95%,-ve predve value 99%.
Clotting and fibronlytic factors • Activation as a result of inection, are significantly raised in infected infants rather than non-infected. • Can be elevated in sick babywith RDS. 1.Thrombin-antithrombin III comples. TAT 2.Plasminogen activator inhibitor-1. PAI-1 3.Plasminogen tissue activator. tPA 4.D-dimer 5.Fibrinogen
Acute Phase Protiens 1.alpha 1 antitrypsin. 2.CRP 3.Fibronectin 3.Haptoglobin 4.Lactoferrin 5.Procalcitonin PCT • They are produced from the liver as apart of immediate response to infection or tissue injury.
CRP • It synthesised within 6-8hrs of exposure to an infective process or tissue damage.half life=19hrs.and may reach to 1000 fold during an acute phase response. • It has higher sinsitivity and specificity than total neutr and I/T ration. • The [CRP] increase slowly with time .serial measurements at 24-48hrs improve the senst (82-84%).The specft and +ve pred value range from 93- 100%.
Cont.. • High in non-infected conditions:meconium aspr, tissue necrosis,recent vaccination,surgery. • Its very useful in monitoring the progress of treatment and for guiding the ABS treatment. • CRP is considered a highly specific but late marker of infection.
Procalcitonin PCT • It has been shown to be assosiated with neurotransmission,immunemodulation and vascular control during infection and SIRS. • Released from Heaptic and Monocytes. • It begins to rise 4hrs after exposure to baterial endotoxin, peak at 6hrs and remain raised for at least 24hrs, with half life 25-30hrs. • Conc of PCT is low immed after birth, rise to peak at 21-24hrs return to basline by 48hrs ?
Cont… • Rapid colonization of the bact in the GIT followed by translocation of endotoxin through bowel wall. • Superior to CRP, sent and specft 87-100% • Infants with viral infection,non-infected process, as hypoxemia,aspiration syndrome birth trauma,have normal or only slightly high • PCT has reported to be useful in indicating the severity of inection, progress of treatment and prediction outcome.
Chemokines,Cytokines IL6 • Increases sharply after exposure to bact products,and preceds the increase in CRP. • Sensitivity 87-100%, Specificity 93-100%. • At the onset of infection IL6 has the highest sensit 89% and –ve predt value 91% compared with CRP. • The measurement of IL6(early and sensitive) • And CRP(late and specific)in the ist 48hrs of presumed sepsis,yield abetter Sensitivity than other markers.
Cont… One study : IL6 and IL1 receptor antagonist can predict N.Sepsis two days before clinical manifestations ,so early antibiotic treatment. IL8+TNF • They are similar to IL6. • IL8 considered to be highly accurate marker with senst 80-91%.
Cell Surface Markers • It depends in the flow cytometric technology • It can localize the activated markers to aspecific cell type. CD11b • Is an alpha subunit of the beta2 integrin adhesion molecule. • Normally expressed at avery low conct on the surface of non-activated neutrophils. • Its used in DX of early sepsis. • Senst 96-100%, Specificity 100%.
CD64 • CD64 is a highly effective marker for the Dx of lateonset sepsis. • It involved in the process of phagocytosis and intracellular killing of pathogens, so its upregulated by bacterial invasion. • Senst 97%, specf 90% CD45RO • Amemory antigen for T lymphocytes,more useful in detection cong bacterial infection. • Unsuitable for use in NICU. • Needs weeks or months after exposure to the Ag.
Infection markers with prognostic significance • There is an interaction btw proinflammatory (IL6,TNFalpha, INF)and Anti-inflammatory (IL4,IL10) • Persistent high conct of IL10,and high IL10/TNF, suggest poor outcomes. • Others found high IL6/IL10 ratio with poor prognosis • Hypothesis:exaggeration of pro-inflamm activity+inadequate anti-inflamm compensation result in shock,multo-organ failure and death.
Conclusions • The early most sensitive markers are: PCT G-CSF IL6 IL8 CD11B • The late specific marker : CRP CD64 • Use multiple markers combining an early sensitive with alate specific tests will enhance the Dx accuracy. • Serial measurement of infection markers will improve the Dx sensitivity. • LOOk for other causes (non-infective) .