Based on these cutoffs, univariate logistic regression analysis was used to assess each parameter (Table 5). All parameters with their defined cutoffs were statistically significant.
Several parameters were excluded from the final multivariate regression model. Serum phosphate was excluded because there were >40% missing data. Tests for collinearity revealed a relation (variance inflation factor ≥2) between lipase and amylase. Because lipase appeared to be a better predictor of severity on area under the ROC analysis, amylase was excluded from further analysis. The final 2 remaining parameters, lipase and hemoglobin, were analyzed using multivariate logistic regression (Table 5). Only serum lipase ≥7 × ULN was associated with a statistically significant increased risk of severe AP (P = 0.006), with an OR (95% CI) of 10.1 (2.0–51.6) within the multivariate model.
Validation of Predictor(s) of Severe AP
Multivariate analysis was repeated in the validation cohort using the same parameters of serum lipase and hemoglobin. Serum lipase was found to be a statistically significant risk factor for severe AP (P = 0.025), with an OR (95% CI) of 7.3 (1.3–41.5) (Table 5). Hemoglobin was also significant (P = 0.041), with an OR (95% CI) of 0.1 (0.01–0.9).
Serum Lipase ≥7 × ULN as a Predictor of Severe AP
Serum lipase ≥7 × ULN (within 24 hours from time of presentation) was the only statistically significant variable after Dunn-Sidak correction and the only significant predictor in both derivation and validation cohorts. Thus, the performance and clinical applicability of serum lipase as a predictor of course of severity in pediatric AP (ie, sensitivity, specificity, PPV, NPV, PLR, and NLR) were determined. Based on the combined derivation and validation data, serum lipase ≥7 × ULN (within 24 hours from time of presentation) was associated with an OR of 7.1 (95% CI 2.5–20.5; P < 0.001) for developing severe AP. Sensitivity, specificity, PPV, NPV, PLR, and NLR were 85%, 56%, 46%, 89%, 1.93, and 0.27, respectively. Of the 131 patients included in this combined cohorts analysis of serum lipase, 23 patients (17 mild and 6 severe) did not have a lipase recorded within 24 hours of presentation and were treated as missing data.
In the present study, we report the potential utility of serum lipase as an early predictor of severity of pediatric AP. We observed that serum lipase, performed within 24 hours of presentation, was significantly associated with severity of AP in children and adolescents. Those with serum lipase concentrations ≥7 × ULN were significantly more likely to follow a severe course of AP (OR 7.1, P < 0.001). This finding was derived as an independent predictor of severity of AP using multivariate regression and confirmed in a contemporaneous cohort from a separate pediatric hospital. The sensitivity of 85% and NPV of 89% for serum lipase concentrations ≥7 × ULN in predicting severe AP suggest that serum lipase may be used as a screening tool to rule out most severe cases of AP in children. Because the true prevalence of AP in the pediatric population is unknown and may vary geographically (2,4,18), we also presented likelihood ratios (which are independent of disease prevalence) to allow application to different populations and settings. In our study population, the NLR of 0.27 suggests a negative posttest probability of 10.6% (ie, 89.4% of patients with a serum lipase result ≥7 × ULN will have a severe AP course).
The present study is clinically relevant because it may provide a simple tool for screening pediatric patients who are unlikely to develop severe AP. Serum lipase is routinely ordered for the diagnosis of pancreatitis, and therefore its benefit as a prognostic tool is without any additional cost. The ability of serum lipase levels to predict AP severity within 24 hours of presentation can provide clinicians with prognostic information early in the course of disease. This is in contrast to many other scoring systems that require data to be collected at later time points. Predicting severity of AP early in the course of disease is critical to optimizing therapy and deciding intensity of monitoring required. Although the management of AP is primarily supportive, recent reports in adult AP demonstrated improved outcomes for severe AP with early interventions such as early aggressive intravenous fluid resuscitation (19) and early enteral feeding (within 1–2 days after developing severe AP) (20–22).
Hemoglobin was not statistically significant on univariate and multivariate analyses of the derivation cohort; however, it was statistically significant in the smaller validation cohort (OR 0.1, P = 0.041). We speculate that this is because of the increase or decrease in hemoglobin, which may occur in patients with severe AP. Increases may occur with intravascular hypovolemia (from 3rd space losses and/or dehydration), whereas decreases may occur with hemorrhagic pancreatitis, gastrointestinal hemorrhage, or hemodilution from aggressive intravenous fluid resuscitation.
In the largest comparison of scoring systems based on pediatric patients with AP, the DeBanto, Ranson, and Modified Glasgow scoring systems performed with: sensitivities of 48.2%, 51.8%, and 51.8%, respectively; specificities of 77.4%, 86.5%, and 88.4%, respectively; PPVs of 43.5%, 58.0%, and 61.7%, respectively; and NPVs of 80.5%, 83.2%, and 83.5%, respectively for severe AP (14). Similar findings were also observed in another separate but smaller comparative study based on Japanese children with AP (15). Hence, the performance of the pediatric-specific DeBanto scoring system was not superior to adult-derived scoring systems as initially reported. Therefore, serum lipase ≥7 × ULN has the advantage over other scoring systems in pediatric AP because it provides a simple, highly sensitive tool, with high NPV, to rule out most cases of severe AP within the first 24 hours of presentation. The NPV of 89% suggests an 89% probability of not developing severe AP in a patient with serum lipase <7 × ULN; however, the low specificity and PPV means that a serum lipase level ≥7 × ULN does not imply a high likelihood of developing severe AP; indeed, only 46% of such patients in our cohort had severe AP. Nonetheless, serum lipase may be used to complement other existing predictive systems because of the differences in performance (sensitivity and specificity) and optimal timing of application. Serum lipase may be used for risk stratification (to rule out most cases of severe AP) within 24 hours of presentation, whereas scoring systems such as the DeBanto, Ranson, or Modified Glasgow could be applied after 48 hours to provide adjunctive prognostic information.
Of note, serum lipase and amylase have not been shown to correlate with severity of AP in previous adult studies (23,24); however, the differences in study design and methodology may explain this discrepancy. Lankisch et al (24) arbitrarily used ≥3 × ULN as cutoffs for both serum lipase and amylase to predict severity, whereas Winslet et al (23) evaluated serum amylase rather than serum lipase levels. In our study, we found serum lipase to be a better predictor of severity than amylase within 24 hours from time of presentation. One explanation for this is that the half-life of lipase (6.9–13.7 hours) is much longer than amylase (2–2.2 hours) (25), making fluctuations less likely. A recent pediatric study also reported lipase to be a better diagnostic marker of pancreatitis than amylase, particularly in infants (26). A positive correlation between serum pancreatic enzyme levels and disease severity has also been observed in a murine study, in which taurocholate-induced severe necrotizing pancreatitis was compared with cerulein-induced mild pancreatitis and a sham control (27). Both serum lipase and amylase were significantly higher in the taurocholate group than the cerulean-induced group at 6, 12, and 24 hours postadministration. Interestingly, this difference was not seen at 48 hours because serum enzyme levels had returned to normal. These findings provide support for a correlation between severe forms of pancreatitis and higher serum pancreatic enzyme levels, as well as the assessment of serum pancreatic enzyme levels early in the course of disease. It may also explain why previous studies, which used a later cutoff (eg, 48 hours), did not find this association. The importance of lipase measurement in clinical practice is also highlighted by 2 recent studies demonstrating lipase elevation to be predictive of biliary tract disease in both adults (28) and children (29).
The proportion of severe cases of AP in our combined cohorts was 29.8%, marginally higher than previous reports of 20% to 28% (13–15). We suggest that this may be because of the fact that the derivation and validation cohorts were derived from tertiary pediatric referral hospitals. Although there is presently no consensus on the definition of severe AP in children, the criteria used in the present study were similar with previous studies (13,14). Our criteria were designed to focus on the development of local (excluding pseudocyst formation) and systemic complications, and the need for pancreatic surgery (distal pancreatectomy and laparotomy). Consensus guidelines in pediatric AP are required to improve the quality and reproducibility of future large, multicenter, prospective studies.
The present study has several limitations. Because it is retrospective, not all patients had blood tests performed within 24 hours of presentation and data collection was limited by the availability of medical records. There were 8 children (6 severe and 2 mild AP cases) who were referred to the study institutions after presenting initially at a referring center. Results for these patients were taken from the referring institution to ensure results were within 24 hours of initial presentation. As previously mentioned, 23 of 131 patients (17.5%) did not have a serum lipase recorded within 24 hours of presentation. Because of the small sample size, other potentially significant parameters may not have reached statistical significance. Nonetheless, we collected data from 2 separate major pediatric referral centers to test validity and ensure generalizability of our findings. Further large multicenter prospective studies involving subjects from different demographics and regions are needed to properly validate our findings, as well as to determine other potential markers to predict the severity of pediatric AP. In the present study, we did not investigate the effect of etiology on severity of AP because our aim was to identify early predictors of severity based on laboratory parameters available in the first 24 hours of presentation. Moreover, the etiology of pancreatitis is often unclear in children, especially early in the course of the disease. With larger multicenter studies, it may be possible to risk-stratify patients as per etiology. The frequency of common causes of AP in the present study is consistent with previous reports in pediatric pancreatitis (13,30).
In conclusion, we have identified and validated the potential use of serum lipase as a simple early predictor of severity in pediatric AP; those with serum lipase levels <7 × ULN within 24 hours of presentation are highly likely to follow a milder course. The ability to risk-stratify pediatric patients within 24 hours of presentation may allow for early targeted interventions and lead to improved outcomes in pediatric patients with AP.
The authors thank Professor Andrea Rita Horvath and Keith Westbury, South Eastern Area Laboratory Services; Marcin Pasternak, Jacqueline Chao, and Filip Tota, Prince of Wales Medical Records; and Dr Huy Tran, Hunter Area Pathology Service.
Renkin's milk antirickets advertisement, 1925. Photo courtesy of the subject, Philip R. Harris, PhD.
Cod liver oil had been recommended for rickets as early as 1824, but causative factors and cures eluded the medical community until the 20th century. The near absence of rickets from sunny countries, such as Egypt, and fish-consuming countries, such as Japan, made little impression. In 1909, Georg Schmorl (1861–1932) in Denmark examined the bones of infants dying between the ages of 2 and 48 months. He ascertained, to the astonishment of all, that nearly 90% of those studied had evidence of rickets. A series of monographs published between 1908 and 1912 by Russian Isidore Schabad (1870) established that cod liver oil prevented rickets as well as cured it. In Berlin, Kurt Huldschinsky (1883) in 1919 used artificial heliotherapy to treat rickets, and in New York, the research of Alfred Hess (1875–1933) confirmed Huldschinsky's findings.
Biochemical studies continued with the research of John Howland (1873–1926) and Benjamin Kramer (1887–1972) who developed a semimicro method for serum calcium and phosphorus measurements. With the advent of the x-ray, they were able to study the evolution and progress of the osteopathy. Edward Parks (1877–1969) and Elmer McCollum (1879–1967) further refined the work of Howland and Kramer using rats as animal models and studying dietary as well as rachitic factors.
At the 1921 American Pediatric Society meeting, sunlight and cod liver oil antirachitic factor were discussed, triggering a cascade of research into the solar irradiation of dermal provitamins. Vitamin D finally was identified as the curative agent, found in the barely palatable cod liver oil. When Philip C. Jeans (1883–1952) in 1936 convinced the Commission on Foods and the American Medical Association to mandate supplemental vitamin D be added to cow's milk, future generations of children were spared the disagreeable taste of cod liver oil and the development of rickets.
—Contributed by Angel Colón, MD
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Keywords:Copyright 2013 by ESPGHAN and NASPGHAN
acute pancreatitis; lipase; pediatric; severity