Journal of Clinical Neonatology

ORIGINAL ARTICLE
Year
: 2022  |  Volume : 11  |  Issue : 2  |  Page : 86--89

Predischarge screening of neonates with transcutaneous bilirubinometer: Comparison of various nomograms


Thrilok Natarajan1, Ramesh Srinivasan2, Sumathi Raju2, Suvetha Kannapan3,  
1 Department of Pediatrics, Queen Alexandra Hospital, Portsmouth, England, UK
2 Department of Pediatrics, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India
3 Department of Community Medicine, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India

Correspondence Address:
Ramesh Srinivasan
Department of Pediatrics, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu
India

Abstract

Objective: To compare the diagnostic accuracy of various transcutaneous bilirubin (TcB) nomograms for predischarge screening. Methods: The paired total serum bilirubin (TSB) and TcB measurements collected in neonates ≥35 weeks and ≥2000 g birth weight were analyzed. BiliCare™ bilirubinometer was used for TcB measurement. We chose the following nomograms for the study: Bhutani nomogram, Maisel's nomogram, Agarwal nomogram, Thakkar nomogram, American Academy of Pediatrics (AAP) nomogram within 3 mg/dl of phototherapy cutoff, AAP nomogram >70% of phototherapy cutoff and if TcB value is above 13 mg/dl. The diagnostic accuracy of these nomograms for TcB was compared with TSB plotted in the Bhutani nomogram. Results: TcB showed a positive correlation with TSB (Pearson correlation coefficient = 0.783). Bhutani nomogram, Maisel's nomogram and AAP (using within 3 mg/dL cutoff) nomogram showed good sensitivity and low false-negative rate while avoiding blood draws in most neonates. Conclusion: Bhutani nomogram, Maisel's nomogram, and AAP (using within 3 mg/dL of phototherapy cutoff) nomograms have comparable diagnostic accuracy for predischarge bilirubin screening in neonates.



How to cite this article:
Natarajan T, Srinivasan R, Raju S, Kannapan S. Predischarge screening of neonates with transcutaneous bilirubinometer: Comparison of various nomograms.J Clin Neonatol 2022;11:86-89


How to cite this URL:
Natarajan T, Srinivasan R, Raju S, Kannapan S. Predischarge screening of neonates with transcutaneous bilirubinometer: Comparison of various nomograms. J Clin Neonatol [serial online] 2022 [cited 2022 Jun 29 ];11:86-89
Available from: https://www.jcnonweb.com/text.asp?2022/11/2/86/343416


Full Text



 Introduction



Neonatal jaundice is most commonly a physiological condition which does not require any intervention. A transient rise in serum bilirubin occurs in almost all neonates in the first few days of life. However, in a few neonates, it can increase to a high level causing pathological jaundice and this requires urgent treatment to prevent neuronal injury. Hence, the American Academy of Pediatrics (AAP) recommends routine predischarge screening of serum bilirubin in neonates to predict the need for treatment and decide the time for follow-up.[1],[2] In recent years, transcutaneous bilirubin (TcB) measurement is used as an instant and noninvasive method of estimating serum bilirubin. Significantly high values in TcBometer have to be confirmed with total serum bilirubin (TSB), estimated by conventional laboratory methods. However, interpreting TcB values is complicated by the availability of various nomograms and the best among them is yet to be determined.[3] In addition, separate nomograms were also developed for the racially different population with diverse skin colors, as TcB measurement relies on light penetration through the skin and it is believed that differences in skin pigmentation may result in variation in TcB measurement.[4] A study to determine the best of the available nomogram for TcB measurement was done by Taylor et al. in which they have compared only the AAP phototherapy nomogram and Bhutani nomogram.[3] Hence, we aimed to compare the diagnostic accuracy of various TcB screening nomograms for predischarge bilirubin screening of neonates.

 Methods



This cross-sectional study was performed in a tertiary care hospital in India during June and July 2020. The hospital procured a new BiliCare™ bilirubinometer in June 2020. In the initial months of using this new equipment, predischarge bilirubin screening of neonates was done with TSB and along with that TcB was measured, as a step to validate the TcB readings. TSB and TcB levels were measured within a span of 1 h. The data collected during this transition phase were used for the study. Healthy neonates ≥35 weeks and ≥2000 g birth weight in the postnatal wards were included in the study. Neonates with postnatal age >7 days, readmitted babies and those under or have received phototherapy were excluded from the study. The institutional ethics committee approval was obtained.

The data of baseline demographic characteristics such as gestational age, birth weight, gender, and Coomb's test were collected. TcB levels were measured using BiliCare™ bilirubinometer (Gerium Medical Limited, Israel). This is a light-emitting diode based device which uses transmission technology and measures the bilirubin level with a probe clipped to the scaphoid fossa of the baby's ear.[5] The device emits light at two wavelengths (blue and green) and measures the transmittance of light as it passes through the tissue with a sensor on the receiving side. The device was calibrated daily. All TcB measurements were performed by either of the two nurses trained to use the device. The average of three measurements was taken as the final TcB value. TSB was measured in venous blood by the diazo endpoint method (Cobas® analyzer, Germany).

We chose the following nomograms for the study: Bhutani nomogram, Maisel's nomogram, Agarwal nomogram, Thakkar nomogram, AAP phototherapy nomogram and if TcB value is >13 mg/dl. The threshold levels recommended for these nomograms were as follows: TcB value above 75th centile in Bhutani nomogram,[6] TcB value >95th centile in Maisel's nomogram,[7] TcB value >50th centile in Agarwal nomogram,[8] TcB value >50th centile in Thakkar nomogram,[9] TcB value >13 mg/dl,[6] TcB value >70% of phototherapy cutoff as per AAP nomogram[3] and TcB value within 3 mg/dL of phototherapy cutoff as per AAP nomogram.[3]

The TcB values were considered as screen positive if the values were above the threshold levels in the decision rules mentioned above. TSB plotted in the Bhutani nomogram was considered as the gold standard to identify infants at high risk of developing significant hyperbilirubinemia. If TcB screening was positive and the paired TSB plotted in Bhutani nomogram fell in high risk or high intermediate risk zone (i.e., >75th centile) then it was considered as true positive.

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 24 (IBM SPSS statistics company, IBM Corporation, Chicago, Illinois, US). Based on a previous study,[3] a minimum sample size of 57 was required for a positive predictive value of 3.8%, α error 5% and 95% confidence interval. Descriptive statistics were used to summarize population characteristics. The sensitivity, specificity, positive predictive value, negative predictive value, and false negativity rate were calculated for each TcB nomogram. In addition, the percentage of blood draws avoided, defined as ([True negatives + False negatives]/Total paired TSB-TcB measurements) were calculated.[3] We defined the best TcB based nomogram as the one with good sensitivity and low false-negative rate in identifying neonates with high TSB levels while avoiding blood draws in most neonates.

 Results



During the study period, 74 neonates had paired TcB-TSB values measured. The baseline demographic characteristics of the study population are shown in [Table 1]. TcB overestimated TSB in 50 (67.56%) samples, underestimated TSB in 22 (29.72%) samples and was the same as TSB in 2 (2.7%) samples. The difference between TcB and TSB was ≤1 mg/dL in 26 samples (35.1%), ≤2 mg/dL in 54 samples (71.6%) and ≤3 mg/dL in 67 samples (90.5%). Pearson's correlation coefficient (r) between TcB and TSB was 0.783 (p = 0.000) with a correlation of determination (r2) of 0.61. The diagnostic accuracy and blood draw avoided with various nomograms are shown in [Table 2].{Table 1}{Table 2}

 Discussion



It is arduous to unequivocally recommend a single nomogram over the others. Hence, a combination of three statistical parameters namely sensitivity, false-negative rate and percentage of blood draws avoided were considered to arrive at a decision. Based on the results of our study, TcB above 75th centile in Bhutani nomogram, TcB above 95th centile in Maisel's nomogram and TcB within 3 mg/dL of phototherapy cutoff in AAP nomogram were considered as better nomograms to screen neonates for jaundice before discharge. Bhutani et al. compared the TcB values with paired TSB values using ≥75th percentile as a cutoff in the Bhutani nomogram and got a sensitivity of 100% with a negative predictive value of 100%.[10]

Taylor et al. have compared ≥75th percentile in Bhutani nomogram, >70% of the phototherapy cutoff in AAP nomogram and within 3 mg/dl of the phototherapy cutoff in AAP nomogram. They found out that though all the three nomograms yielded a low false-negative rate (<10%) while avoiding blood draws in 80%–90% of occasions, AAP nomogram-based decisions were preferable in view of more blood draws avoided.[3] In our study, although >70% of phototherapy threshold in AAP nomogram had good sensitivity and low false-negative rate, the percentage of blood draws avoided is less (41.6%). Both Agarwal and Thakkar nomogram has 100% sensitivity and 0% false-negative rate but the percentage of blood draw avoided is very low. The TcB >13 mg/dL rule has low sensitivity and high false-negative rate.

Our study emphasizes that each nomogram has its own strengths and weaknesses. Bhutani nomogram is recommended by AAP for predischarge screening using TSB.[1] Hence using the same nomogram for TcB screening may be easy to adapt in current practice. The AAP nomogram requires accurate risk stratification based on laboratory parameters indicative of hemolysis such as reticulocyte count, peripheral smear, Coomb's test and Glucose 6 phosphate dehydrogenase level.[1] Maisel's nomogram can be used for screening only up to 96 h of life which limits its utility in case of delayed discharge of neonates.[7] Both Agarwal and Thakkar nomogram are TcB based nomograms developed in India and claims superiority for use in Indian neonates.[8],[9] However, Maisels et al. reported no difference in TcB-TSB correlation between different races.[11] TcB >13 mg/dL rule cannot be applied for babies in early hours of life since the phototherapy threshold is low in the early hours of life.[1]

We have compared various nomograms using paired TcB-TSB values which assist to bridge the knowledge gap in the literature. However, babies at low risk of bilirubin neurotoxicity as per the AAP guidelines[1] contributed to 75% of the study population and high-risk babies were in meager numbers. We were not able to arrive at a single best nomogram for TcB screening. Further studies may be done to overcome these limitations observed in our study.

 Conclusion



Predischarge bilirubin screening using TcBometer can be interpreted using various nomograms available. However, Bhutani nomogram, Maisel's nomogram and AAP phototherapy nomogram (using within 3 mg/dL cutoff) have a comparable diagnostic accuracy for predischarge bilirubin screening with almost similar number of blood draws avoided.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest

References

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