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Brief Reports Indian Pediatrics 2001; 38: 278-280 |
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Correlation of Plasma Color Index with Serum Bilirubin in Neonatal Jaundice |
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Neonatal hyperbilirubinemia may require repeated serum bilirubin estimation. The serum bilirubin estimation by Malloy Evelyn(1) method is time consuming, requires more blood and results vary from laboratory to laboratory(2). A non invasive technique-transcutaneous bilirubinometer(3) found a good correlation between its estimates and serum bilirubin levels. However, it was observed that many factors such as phototherapy, exchange transfusion, color of the skin and gestational age affected the reading(3,4). Guha et al. reported a better correlation with filter paper index than jaundicemeter(5). However, this is a costly method. So there is a need to develop a simple, reliable and reproducible method for estimation of serum bilirubin. The present study was designed to evaluate the relationship between plasma color index and serum bilirubin level.
Fifty neonates admitted in pediatric ward with jaundice were studied. Their weight varied from 1.2 to 3.9 kg and age from birth to 10 days (median age 3 days). Serum bilirubin was estimated by two different techniques:
Preparation of potassium dichromate solution: Two gm of potassium dichromate was dissolved in distilled water and the final volume was made to 100 ml which was equal to color index 200. Further dilutions were made as shown in Table 1. The color of plasma was compared with the different dilutions of potassium dichro-mate solutions by naked eye examination. The plasma was assigned the color index to that of the nearest corresponding dilution of potassium dichromate. Statistical methods The correlation coefficient between plasma color index and serum bilirubin (by diazo) was estimated using Plersa’s correlation coeffi-cient. Linear regression equation for predicting serum bilirubin from the color index was derived by the least squares method. No inter or intraobserver comparison was carried out for the naked eye color index estimation.
The mean (sd) total serum bilirubin by the diazo estimate for the 50 neonates was 14.57 (4.4) mg/dl. The mean (sd) color index was 75.0 (21.0). The correlation between serum bilirubin and color index was very high (r = 0.97 p <0.001) (Fig. 1). The regression equation for predicting serum bilirubin from color index was: Color index = 4.62 (S. bilirubin) + 7.67. Thus serum bilirubin estimates can be easily derived from color index.
Estimation of serum bilirubin by using a color index is a simple bedside screening method to know the severity of jaundice, especially since it correlates well with total serum bilirubin level (r = 0.97). In contrast to color index, the results of transcutaneous bilirubinmeter are affected by color of skin, phototherapy and exchange transfusion(4,7). Malloy and Evelyn method(1) is the standard technique in most laboratories but requires more quantity of blood and is more laborius. Micro-modifications of Malloy and Evelyn technique are available but require expensive equipment. The automatic methods give results 10% lower than the manual technique.
Transcutaneous bilirubin estimation studies have reported correlation coefficient ranging from 0.88 to 0.94(3,4). The results of the present study are comparable to those reported by other workers using transcutaneous bilirubinometry. The advantages of color index estimations are that the technique is simple and does not require any sophisticated equipment. Contributors: KKL took part in supervision of data and helped in analysis and drafting; he will act as guarantor of the paper. MS designed the study and conducted analysis. KS, MKB and RG participated in data collection and wrote the draft. MS and RG were involved in data analysis and revising the draft.
Funding:
None.
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