|Year : 2021 | Volume
| Issue : 2 | Page : 59-67
An observational prospective study to compare transcutaneous bilirubin with serum bilirubin in preterm newborn requiring phototherapy
Syamal Sardar1, Nirmalya Sarkar1, Moumita Ghosh2, Somnath Pal1
1 Department of Neonatology, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal, India
2 Department of Pediatrics, Medical College and Hospital, Kolkata, West Bengal, India
|Date of Submission||15-Dec-2020|
|Date of Decision||05-Jan-2021|
|Date of Acceptance||06-Jan-2021|
|Date of Web Publication||15-May-2021|
Assistant Professor, Department of Neonatology, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
Background: Transcutaneous bilirubin is used as a screening tool before starting phototherapy in preterm newborn. However, there is conflicting evidence regarding its utility after starting phototherapy. There is also doubt regarding the best site of measurement. Objective: The objective was to analyze the association between transcutaneous bilirubin and serum bilirubin in Indian preterm newborns at different sites before, during, and after phototherapy. Methods: This prospective observational study was conducted in a tertiary care neonatal unit of eastern India from May 2019 to April 2020. Participants: The study participants were 90 preterm newborns admitted for phototherapy within the first 7 days of life. Intervention: Transcutaneous bilirubin was assessed by Draeger JM-105 at the covered areas of the sternum and forehead and serum bilirubin was assessed by the Diazo method within 30 min of each other. Bilirubin assessment was done before starting phototherapy and then repeated every 12 h till 24 h postphototherapy. Outcome: To determine the correlation and agreement between serum bilirubin and transcutaneous bilirubin in preterm newborns before, during and after phototherapy. Results: Median gestational age and mean birth weight of the enrolled infants were 33.5 weeks and 1920 g, respectively. Transcutaneous bilirubin from sternum demonstrated good correlation with serum bilirubin before (r = 0.856), during (r = 0.723 at 24 h), and after phototherapy (r = 0.801 at 24 h postphototherapy). Measurements from the forehead showed better correlation with serum bilirubin compared to the sternum (r = 0.865 before, 0.732 during, 0.814 after phototherapy). At both sites, correlation worsened with phototherapy but improved gradually in the postphototherapy period. Bland–Altman analysis revealed wide upper limit of agreement between transcutaneous bilirubin and serum bilirubin at both sites and all points of time, suggesting a transcutaneous device significantly overestimated serum bilirubin. Conclusion: There was good correlation but poor agreement between transcutaneous bilirubin and serum bilirubin in Indian preterm newborns irrespective of timing and site of measurement.
Keywords: Bland–Altman plot, correlation coefficient, preterm, serum bilirubin, transcutaneous bilirubin
|How to cite this article:|
Sardar S, Sarkar N, Ghosh M, Pal S. An observational prospective study to compare transcutaneous bilirubin with serum bilirubin in preterm newborn requiring phototherapy. J Clin Neonatol 2021;10:59-67
|How to cite this URL:|
Sardar S, Sarkar N, Ghosh M, Pal S. An observational prospective study to compare transcutaneous bilirubin with serum bilirubin in preterm newborn requiring phototherapy. J Clin Neonatol [serial online] 2021 [cited 2021 Aug 2];10:59-67. Available from: https://www.jcnonweb.com/text.asp?2021/10/2/59/316185
| Introduction|| |
Almost 80% of preterm newborns are affected by neonatal jaundice in the 1st week of life. Neonatal hyperbilirubinemia can lead to neurodevelopmental impairment in preterm newborns at a lower serum bilirubin concentration than term newborns. Although the American Academy of Pediatrics recommends universal screening of all babies for neonatal jaundice, it seems impractical in developing countries with limited resources., As preterm newborns are more susceptible to adverse neurodevelopmental outcomes from neonatal jaundice, frequent monitoring of total serum bilirubin (TSB) is required. However, frequent skin pricks can lead to pain, sepsis, anemia, and adverse neurodevelopmental outcomes by itself. Transcutaneous bilirubinometry (TcB) is an alternative in this situation. Screening with a transcutaneous device may significantly reduce the blood sampling in newborn babies and its use is rapidly gaining popularity in developing countries like India. However, there is doubt regarding the accuracy of TcB in preterm newborns once phototherapy has been started even if it is recorded from the covered areas. Recently, two separate meta-analyses have confirmed the high correlation between TcB and TSB before starting phototherapy both in term and preterm newborns., There is conflicting evidence regarding correlation and agreement between the two methods once phototherapy has been started, especially in preterm newborns. Some studies report high correlation in preterm babies after starting phototherapy (correlation coefficient ranging from 0.69 to 0.89), while others suggest moderate correlation (r = 0.58) between the two.,,, Moreover, majority of these studies were done on the Caucasian population with very few focusing on different ethnic groups., Studies on African newborns revealed significant overestimation of TSB by TcB even before starting phototherapy., Moreover, there is no consensus regarding the ideal site of TcB measurement and clinicians often use the sternum, forehead, abdomen, or interscapular region as per their convenience and manufacturer instructions. We also have no data about the accuracy of TcB under phototherapy at these different sites. Thus, this study was conducted to evaluate the correlation and agreement between TSB and TcB at different sites before, during, and after phototherapy in Indian preterm newborns.
| Methods|| |
This observational, prospective study was conducted in a level III tertiary care neonatal unit of Eastern India from May 2019 to April 2020.
Institutional ethical committee approved the study and it was registered in the Clinical Trial registry India (CTRI/2019/02/017797).
The minimum number of preterm newborns to be included in the study was analyzed by estimating the sample size for correlation testing with the assumption of alpha error of 0.05, beta error of 0.2, and correlation coefficient of 0.3 (Cohen's effect sizes for medium correlation). The total sample size was estimated to be 84 at least.
Selection and description of participants
After obtaining written informed parental consent, all preterm newborns (<37 completed weeks) developing neonatal jaundice and requiring phototherapy for the first time within the first 7 days of life were included in the study. The gestational age of the baby was assessed by the date of maternal last menstrual period or first-trimester dating scan and corroborated with the new Ballard scoring after birth. If the discrepancy was of more than 2 weeks, Ballard scoring was considered as the final estimate of gestational age. Exclusion criteria were parental denial of consent, sick preterm newborns requiring intensive care, extremely low birth weight newborns (ELBW), babies who underwent phototherapy previously, and newborns requiring exchange transfusion. For newborns requiring multiple sessions of phototherapy, bilirubin levels pertaining to the first phototherapy session were only included. Criteria for phototherapy were based on TSB level as per the National Institute for Health and Care Excellence guideline. Intensive phototherapy was provided to each baby with GE Lullaby light-emitting diode unit as per manufacturer instruction. Initiation, continuation, and omission of the phototherapy were based on TSB values only. Phototherapy was continued till serum bilirubin was more than 2 mg/dL below the age-specific cutoff.
Measurement of transcutaneous bilirubin and serum bilirubin
TcB was measured as soon as possible, preferably within 30 min of drawing the blood sample for TSB with Drager JM 105 transcutaneous bilirubinometer. The device was calibrated before each reading. The average of three consecutive TcB readings was taken as the final value. Initial TcB before starting phototherapy was measured at uncovered areas of the sternum and forehead. Thereafter, two small opaque circular disposable electrocardiogram (ECG) leads of 2.5 cm diameter covered with aluminum foil were attached to the forehead and sternum to shield these sites from the phototherapy light. These opaque ECG leads were kept in position till 24 h postphototherapy. All TcB measurements during and after phototherapy were taken from these covered sites. In addition, a separate TcB reading was taken simultaneously from the adjacent uncovered area as a control. Bilirubin assessment was done before starting phototherapy and then repeated serially every 12 h till 24 h postphototherapy to check for the rebound increase in bilirubin. Venous blood sample drawn for bilirubin assessment was sent immediately to the institutional central laboratory. Serum bilirubin was assessed by Diazo reaction and fractionated.
Demographic details were collected from the maternal records. Etiology of the jaundice was sought by history, physical examinations, and relevant investigations. The etiology of neonatal jaundice was categorized into hemolytic and nonhemolytic varieties for further analysis. Hemolytic neonatal jaundice was diagnosed in presence of falling hematocrit, elevated reticulocyte index with any of the following – positive direct Coombs test, G6PD deficiency, abnormal peripheral blood smear, or maternal and infant blood group incompatibility.
Primary outcome of the study
- To determine the correlation and agreement between TSB and TcB before, during, and after discontinuing phototherapy
- To assess the correlation and agreement between TSB and TcB at different sites of measurement (sternum and forehead).
The secondary outcome was to assess the correlation and agreement between TSB and TcB
- In hemolytic and nonhemolytic categories of neonatal jaundice
- In different gestational age groups (≤33 and ≥34 weeks).
The study population was tested for normality using the Shapiro–Wilk test. Continuous variables were displayed as mean (standard deviation [SD]) for normally distributed data and as median (interquartile range [IQR]) for skewed data. Categorical variables were presented as frequencies and percentages. Agreement between TcB and TSB was tested by Bland–Altman analysis. Association between TSB and TcB was analyzed by the Pearson product-moment correlation test. One-way ANOVA with post hoc analysis was used to compare TcB measured from uncovered areas to TcB obtained from the covered areas of the sternum and forehead. The mean of the difference between TcB and TSB (TcB–TSB) at each site was analyzed by one-sample t-test to identify the presence of any systemic bias of measurement. All study outcomes were analyzed on SPSS software version 23 (IBM corporation, Armonk, NY, USA) with P < 0.05 considered statistically significant.
| Results|| |
Out of 171 preterm newborns admitted in the unit for phototherapy during the study period, 81 were excluded (52 babies were ELBW or required admission in the intensive care unit, 25 babies received phototherapy previously, and parents of 4 babies denied consent for the study). Thus, a total of 90 babies were included in the study with a median (IQR) gestational age of 33.5 (31, 35) weeks and mean (±SD) birth weight of 1920 (±505) g. 18 babies had evidence of hemolysis. The mean (±SD) age at starting phototherapy was 49.8 (±20.32) h with a median (IQR) duration of phototherapy of 36 (24, 36) h. 22 babies required readmission within 24 h of stopping phototherapy. Demographic details and baseline characteristics of the enrolled infants are shown in [Table 1].
|Table 1: Demographic details and baseline characteristics of the study population|
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Regarding primary outcome, both TcB measured at the sternum and forehead demonstrated fairly good correlation with TSB before, during, and after phototherapy [Table 2]. TcB forehead showed a slightly better correlation with TSB at each point of time. The best correlation was noticed before starting phototherapy which progressively decreased with increasing duration of phototherapy. Correlation again improved in the postphototherapy period and more improvement was noticed with greater passage of time. Correlation almost became similar to prephototherapy session 24 h after stopping phototherapy [Table 2]. A similar trend of correlation was noticed across different gestational age groups [Table 3] and hemolytic category of neonatal jaundice [Table 4]. To assess the effectiveness of opaque ECG leads as light-shielding agent, TcB was measured simultaneously from an uncovered area adjacent to the covered area. Opaque ECG leads were kept in place till 24 h postphototherapy. TcB from the uncovered area was significantly lower than the TcB recorded from the covered areas during and after phototherapy (P < 0.001) [Table 5]. Considering the linear relationship between TcB and TSB, a regression equation was constructed to estimate the value of TSB from the TcB sternum and forehead at each point of assessment [Table 6]. However, a good correlation does not always suggest a good agreement between parameters. As a priori, we defined the maximum limit of agreement (LOI) between TcB and TSB to be ± 2 mg/dL. In spite of good correlation, there was a wide LOI between TSB and TcB exceeding the priori set limit at both sites and all points of time. In Bland–Altman plots, the upper LOI between TcB sternum and TSB varies from + 3.235 before phototherapy [Figure 1], +6.23 at 24 h of phototherapy [Figure 2], upto + 3.918 24 h after stopping phototherapy [Figure 3]. Corresponding values between TcB forehead and TSB vary from + 4.988 before phototherapy [Figure 4], +6.241 at 24 h of phototherapy [Figure 5], upto + 4.082 24 h after stopping phototherapy [Figure 6]. This suggests that the TcB forehead overestimates TSB even further than the TcB sternum despite better correlation. Unlike upper LOI, lower LOI between TcB and TSB remained within 2 mg/dL, on most occasions suggesting that overestimation of serum bilirubin by TcB is much more likely than underestimation. The mean and 95% confidence interval of the difference between TcB and TSB was significantly higher than 0, which also suggests that TcB significantly overestimates TSB irrespective of the site of measurement. In addition, this difference progressively widens with increasing duration of phototherapy pointing to the fact that the tendency of TcB to overestimate TSB also worsens under phototherapy [Table 7].
|Table 2: Correlation between total serum bilirubin and transcutaneous bilirubin before, during, and after phototherapy|
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|Table 3: Correlation between transcutaneous bilirubin and total serum bilirubin in late preterm newborns (34 weeks-366/7 weeks)|
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|Table 4: Correlation between transcutaneous bilirubin and total serum bilirubin in babies with hemolytic neonatal jaundice|
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|Table 5: Comparison between transcutaneous bilirubin measured from covered and uncovered areas during and after phototherapy|
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|Table 6: Regression equation of total serum bilirubin from transcutaneous bilirubin sternum and transcutaneous bilirubin forehead before, during, and after phototherapy|
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|Figure 1: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry sternum before phototherapy|
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|Figure 2: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry sternum at 24 h of phototherapy|
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|Figure 3: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry sternum 24 h after phototherapy|
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|Figure 4: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry forehead before phototherapy|
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|Figure 5: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry forehead at 24 h of phototherapy|
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|Figure 6: Bland–Altman plot between total serum bilirubin and transcutaneous bilirubinometry forehead 24 h after phototherapy|
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|Table 7: Difference between transcutaneous bilirubin and total serum bilirubin before, during, and after phototherapy|
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| Discussion|| |
This study evaluates the relation between TcB and TSB in Indian preterm newborns before, during, and after stopping phototherapy, measured in the forehead and sternum. Earlier studies on TcB concentrated mostly on term newborns.,, In the last decade, the focus has been shifted to its application in preterm newborns. A meta-analysis by Nagar et al. confirmed high correlation between TcB and TSB (r = 0.83) in preterm newborns before initiation of phototherapy. Our study also found a similar correlation before starting phototherapy (r = 0.856 at the sternum and 0.865 at the forehead). However, majority of the studies in the meta-analysis enrolled infants from Caucasian backgrounds with only a few focusing on different ethnicities. Moreover, it only included data from prephototherapy measurements with earlier generation transcutaneous devices (Bilicheck, JM-102, JM-103). On the other hand, studies evaluating the accuracy of transcutaneous devices after starting phototherapy yield a wide range of correlation coefficients. Moreover, the agreement between the two methods of bilirubin assessment varies substantially across studies. This variation depends on the ethnicity of the population, type of bilirubinometer, and timing of assessment in relation to phototherapy. A study on Indian preterm newborns of 28–37 weeks gestation found that TcB from unexposed sternum correlated significantly with TSB before (r = 0.903) and 12 h after starting phototherapy (r = 0.918). However, there was a wide LOI, with a upper bound of +3.5 and a lower bound of −2, similar to our study. In another Indian study of late preterm and term infants, although the correlation between patched TcB sternum and TSB was moderate (r = 0.43–0.79), there was poor agreement at each point of time before, during, and after phototherapy. On the other hand, in a study from Spain using JM-105, there was both good correlation and agreement in preterm newborns before and during phototherapy. The mean difference between patched TcB and TSB varies from − 0.82 to 0.87 during phototherapy and maximum agreement was reached at 48 h of treatment. Overall, there is a tendency to overestimate serum bilirubin by the transcutaneous device after starting phototherapy. As dermal bilirubin in the covered area does not isomerize, it retains the original bilirubin concentration while the serum bilirubin decreases under the effect of phototherapy. This mismatch leads to overestimation by a transcutaneous device in the patched areas during phototherapy. In our study, we noticed a worsening trend of correlation after initiating phototherapy which improved gradually in the postphototherapy period. The mean difference between TcB and TSB also increased during phototherapy. The overestimation in the patched areas could explain the falling correlation and wider agreement between TcB and TSB during phototherapy compared to the prephototherapy measurement. Only a few studies have attempted to analyze the relation between TcB and TSB in postphototherapy session., There is a trend of improvement in the correlation after stopping phototherapy which is also found in our study. The question remains whether we can use TcB as an alternative to serum bilirubin after starting phototherapy. The wide LOI between TcB and TSB beyond the clinically acceptable range poses a concern about using TcB in the present scenario. Although the agreement improved a bit after stopping phototherapy, it remained more than the acceptable range of ±2 mg/dl, limiting its clinical utility even in the postphototherapy period.
We also tried to analyze the relation between TcB and TSB according to the site of TcB measurement which has not been attempted in earlier studies. In our study, the TcB forehead had a better correlation with TSB irrespective of the timing of measurement. However, the tendency to overestimate serum bilirubin was even greater at the forehead, which leads to a wider range of agreement. Unlike this study, meta-analysis by Nagar et al. did not find any difference in the correlation and precision of measurement at different sites. As jaundice in newborns progresses cephalocaudally, TcB forehead could be higher than TcB sternum explaining the wider agreement between TcB and TSB at the forehead compared to the sternum. However, this does not explain the better correlation at the forehead. Correlation between TcB and TSB depends on the texture and thinness of the premature skin. The difference in skin characteristics between the forehead and sternum might be the reason behind the difference in correlation at these two sites of measurement. More studies are required to ascertain the ideal site of TcB measurement, especially in Indian preterm newborns.
Regarding the secondary outcomes of our study, no difference in correlation was found across different gestational age groups (≤33 and ≥34 weeks) and different etiologies of neonatal jaundice (hemolytic versus nonhemolytic). Very few studies have evaluated these differences previously. A study comprising of 30 Indian preterm newborns of 28–37 weeks gestation found that TcB at 28–32 weeks of gestation (r = 0.97) was better correlated with TSB than TcB of babies with gestational age 32–37 weeks (r = 0.88). They have attributed the difference to the skin immaturity of the very preterm babies (<32 weeks gestational age). We could not find any previous study evaluating the correlation of TcB and TSB based on the difference in etiologies of jaundice.
There are several strengths of our study. It comprises exclusively of Indian preterm newborns; therefore, the results will be relevant in the Indian scenario. In addition to robust methodology and adequate power, we have also used the latest version of the transcutaneous bilirubinometer (Draeger JM105). However, there are few limitations as well. We have excluded ELBW babies because of their sickness, hence the relation between TcB and TSB could not be tested in the most premature babies. Due to the unavailability of the standard photo opaque patch (BiliEclipse) in our institution, we used opaque ECG leads covered with aluminum foil as an alternative to shield the sites from phototherapy lights. However, it was proved to be quite effective as evidenced by the significant difference between TcB measured from the covered and uncovered areas.
| Conclusion|| |
TcB measured both at the sternum and forehead shows good correlation with TSB before, during, and after phototherapy. Correlation is better at the forehead compared to the sternum. However, there is poor agreement between TcB and TSB at both sites and all points of time which worsened after starting phototherapy. Due to wide LOI, TcB has limited utility in monitoring jaundice in Indian preterm newborns requiring phototherapy. No difference in correlation was found across different gestational age groups (≤33 and ≥34 weeks) and different etiologies of neonatal jaundice (hemolytic versus nonhemolytic).
The authors deeply appreciate the contributions of nursing staffs and residents of the neonatal unit of IPGMER, Kolkata, India, toward this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]