Immunoreactive trypsin levels in neonates with ... - ResearchGate

Pediatr Surg Int (2006) 22: 236–239DOI 10.1007/s00383-005-1614-3ORIGINAL ARTICLEL. C. Steven Æ G. Gavel Æ D. Young Æ R. CarachiImmunoreactive trypsin levels in neonates with meconium ileusAccepted: 24 November 2005 / Published online: 3 January 2006Ó Springer-Verlag 2006Abstract Serum immunoreactive trypsin (IRT) is used asa screening test for cystic fibrosis (CF) in neonates inmany countries. Variations in IRT levels are observed inhealthy and cystic neonates within the first few weeks oflife. Fifteen percentage of CF neonates present withmeconium ileus (MI). We hypothesised that there maybe differences in serum IRT levels in cystic babies withsimple and complicated MI. The aim of this study was toinvestigate the serum levels of IRT in neonates with CFpresenting with MI. IRT levels were sequentially measuredin neonates (n=29) with CF with intestinalobstruction due to simple or complicated MI. Thesewere compared to levels obtained from non-cysticneonates/controls admitted with a variety of other intraabdominalpathologies (n=49) IRT levels were significantlyhigher in the CF–MI group than the non-cysticcontrols (P99th centile) obtainedby dry blood spot testing (Guthrie card) is used to screenfor CF in many countries. The diagnosis of CF is thenconfirmed by genetic analysis and/or a positive pilocarpineiontophoresis sweat test. The two-tier strategycombining an elevated IRT level and genetic analysis hasallowed a higher sensitivity and specificity in CFscreening [1]. There remains debate as to the true clinicalbenefit of CF screening, the cut off level for an abnormalIRT value and the optimum timing of the screeningsamples which may be complicated by a well-recogniseddecline in serum IRT in CF infants [2].It has been suggested that cystic babies presentingwith meconium ileus (MI) may have normal or high IRTlevels [2–4]. We hypothesised that there may be differencesin the IRT levels in the cystic neonates with simpleand complicated MI.We report the results of serum IRT levels measured in29 neonates diagnosed with MI with CF. These werecompared with IRT levels in 49 neonates without CF,but with abdominal pathology presenting to the neonatalsurgical unit.Materials and methodsThe study was performed at the tertiary paediatricreferral centre of the west of Scotland, with consecutiveenrolment of patients over a 6-year period. IRT levelswere measured on dry blood specimens taken by heelprick onto blotting paper taking care to carefully cleanthe skin to reduce the incidence of faecal contaminationwhich may have resulted in a falsely high IRT level. Due

237to the time period of the study three different assayswere used to determine the 99th centile IRT value foreach assay was taken as a relative value of 1.0 in order tofacilitate comparison (Table 1).There was no set protocol as to the exact timing ofthe samples. The initial samples for all patients weretaken soon after presentation to our unit. Subsequentsamples were taken during blood sampling for haematologyor biochemistry specimens.For statistical analysis, between group comparisonswere performed using t tests or Mann–Whitney tests andwithin group comparisons were done using paired t testsor Wilcoxon tests. Non-parametric tests were used whenthe normality assumption was found not to be valid. Allanalyses were done using Minitab (Version 14) with asignificance level of 5%. Results are expressed as Pvalues (unadjusted for multiple comparisons) with 95%confidence intervals.ResultsGroup 1: Simple and complicated MI in CF neonatesTwenty-nine surgical neonates with intestinal obstructiondue to MI had a total of 63 IRT values assayed(range 1–4, mean 2.17 samples) with 90% of the patientshaving 2 or more IRT samples taken. All babies weresubsequently confirmed to have CF by cytogeneticanalysis; DF508 homozygous (n=22), DF508 heterozygous(n=4) and the remainder having less commongenotypes.The group was subdivided into simple (n=21) andcomplicated (n=8) MI, e.g., presence of atresia, volvulus,meconium peritonitis or giant meconium cyst. Furthersubdivision of the simple group was made as ninebabies, initially treated conservatively, required operativeintervention due to failed non-surgical managementof their MI (n=4), delayed obstruction (n=2) or due tocomplications of administered enemas (n=3). All babiesin the complicated group underwent operation. Therewas one early death in the simple group due to caecalperforation and one late death in the complicated groupfrom sepsis and respiratory failure.Although relative IRT values for the first sampleswere higher for the simple MI group (Table 2), formalcomparison of the simple and complicated MI patientsTable 1 The IRT assay values for the 99th centile for the normalneonatal population, units micrograms/litreType of Assay 1-week age 6-week ageWholebloodSerumWholebloodSerumSorin reagents 60 120 45 100Agen reagents 45 100 40 90DELFIA fluorometric 60 120 60 120Table 2 Mean and median IRT relative ratio levels for the firstIRT measurement for each groupshowed no evidence of any difference in the IRT ratiovalues (Mann–Whitney P=0.4349, 95% CI) (Fig. 1).Comparison of sex, gestation (P=0.14) and birthweight (P=0.849) parameters showed no evidence ofany statistical difference nor did comparison of pre- andpost-operative values (P=0.654) in the simple or complicatedMI group.Two babies whose initial IRT relative ratios wereconsidered normal, i.e. relative value

238Fig. 1 Boxplot comparingrelative IRT values for thesimple and complicatedmeconium ileus groupstwo (7%) CF patients in the MI group were the initialIRT relative ratios considered normal but were elevated,i.e. >99th centile, on repeat testing 9 and12°days later. This finding highlights the importance offormally retesting or screening all neonates presentingwith MI for CF. In the control group, one neonatewith delayed passage of meconium had a persistentlyraised serum IRT level representing a false positive rateof 2%. Raised IRT levels have been noted in sickneonates without CF, but it would seem that thoseconditions where one might expect a degree of pancreaticstasis, e.g. exomphalos, gastroschisis, small bowelatresia did not show disproportionately raised IRTlevels [5]. One might have hypothesised that IRT levelswould be higher in those with simple MI with continuedstasis and obstruction of the pancreatic ducts andretrograde IRT absorption, compared with complicateddisease and perforation. This was not demonstrated inour study.This study is underpowered and we would require 64patients in each of the simple and complicated MIgroups to achieve adequate powering. This would equateto a 48-year time period to complete the data collection.It may be that with adequately powered study moreobvious trends in the IRT levels may be apparent. Asour hospital is a tertiary referral centre there is often aninevitable delay in the babies reaching us, meaning thatage at presentation and time of initial IRT samplingcould not be standardised.There remains debate as to whether cystic neonatespresenting with MI may actually have a different diseaseprofile than those with CF but without MI and that theymay have a better prognosis due to earlier diagnosis. A12-year review [6] found that children with CF and MIhad a higher early mortality rate, mainly due to perioperativedeaths, but the subsequent survival was nodifferent than non-MI patients. Cystic babies with MIhave been shown to be smaller at birth, in both lengthFig. 2 Boxplot comparingrelative IRT values for the MIand control groups

239and weight, and with later malnutrition than thosewithout MI [7]. This would appear to be worse in thesurgically managed MI group than those treated conservatively.Pulmonary function has been shown to besignificantly worse in CF children presenting with MI asmeasured by spirometry and chest radiography comparedto non-MI cystic controls [8]. Several studies havelooked to explain differences in the most common CFgenotypes and subsequent clinical course, including MI,but have failed to identify any consistent trends [9, 10].ConclusionsThe above study outlines our observed variations in IRTlevels in CF neonates presenting with MI. The resultsindicate that IRT levels in patients with neonatal intestinalobstruction due to MI are significantly higher(P