Total Bilirubin Binding Capacity Research Articles

The influence of clinical status on total bilirubin binding capacity in newborn infants

The influence of clinical status on total bilirubin binding capacity in newborn infants

The influence of clinical status on total bilirubin binding capacity in newborn infants.

The relationship between total bilirubin binding capacity (TBBC) and clinical status was investigated in order to assess the risk of bilirubin toxicity in 83 infants with jaundice in this study. Infants with respiratory distress, acidosis, hypoglycaemia, sepsis, asphyxia-anoxia and hypercarbia were accepted as ill and the remainders were well. Sephadex G-25 gel filtration method was used to determine TBBC. Serum albumin levels, TBBC and TBBC/albumin molar ratios were lower in ill premature and mature infants. Acidosis was the major risk factor for bilirubin toxicity in ill infants. Therefore, clinical status should be taken into consideration in the management of jaundiced infants.

Decreased bilirubin binding by albumin in late pregnancy

It is known that the albumin concentration of maternal plasma is reduced at term and that the binding of certain drugs and bilirubin’ in plasma is likewise reduced. This decreased plasma binding of bilirubin may be due to decreased albumin concentrations alone or a decrease in the ability of albumin to bind bilirubin. It is possible that the same factor(s) which causes decreased binding ability in cord blood may decrease the binding ability in maternal blood. We undertook this study to determine if the quantitative binding of bilirubin to albumin (binding fraction) was changed in pregnant women at term. We collected heparinized venous plasma from 19 normal pregnant subjects at term (38+ gestational weeks) and 19 normal, nonpregnant control subjects. Informed consent was obtained from all subjects in this study. Apparent total bilirubin binding capacity was measured by the peroxidase method with pooled human bilirubin-enriched plasma used as a control. Albumin was determined by the bromcresol green method. All assays have been described in detail elsewhere.’ The binding fraction was expressed as the total bilirubin binding capacity/albumin molar ratio. Statistical analysis of the data included calculations of Pearson’s product-moment correlation coefficients and multiple regression analysis. Correlation coefficients were tested for significance with the use of one-tailed t tests. The total bilirubin binding capacity in the pregnant subjects was 20.9? 2.7 (mean? SD) compared to 30.5 2 3.4 in our nonpregnant sample. The albumin concentration was 3.6 * 0.26 compared to 4.6 -C 0.29 and the binding fraction was 0.66 ‘0.11 versus 0.78 * 0.10 for the nonpregnant sample. Fig. 1 shows the relationship of total bilirubin binding capacity to binding fraction in the two groups, along with the respective linear regression equations. We found that the relationship between total bilirubin binding capacities and binding fraction was stronger in nonpregnant women (r = 0.87, p < 0.001) than in pregnant women (r = 0.76, p < O.OOl), probably because there was less spread in the total bilirubin binding capacity in the former group. The binding fraction of the pregnant group was about 15% lower than the binding fraction of the nonpregnant group, whereas

Hemodialysis reduces the unbound phenytoin in plasma

a level ten times the maximum adult level (~ 10 #g/ml) we can estimate the danger of displacing bilirubin from albumin by calculating the maximal displacement factor (MDF) 6 from the equation: MDF=KD(1-q) D+I. In this equation q represents the fraction of drug bound to plasma proteins. Using our observed KD for pancuronium (2.5  102), the reported 70% protein binding 4 and the hypothetical blood level of pancuronium (10 #g/ml), the MDF -- 1.0. Insignificant displacement is thought to occur when the MDF is smaller than 1.2. 8 This describes the relationship of the drug to albumin. It is, however, possible that metabolites of the drug may compete with other substances bound to albumin. The technique used in this study will not resolve this question and further work needs to be done measuring the reserve albumin for bilirubin-binding capacity in patient samples by other methods. In vivo studies of the total bilirubinbinding capacity before and after drug administration are in progress. In the single case so far studied here, there was no significant change in the total bilirubin-binding capacitY after an intravenous injection of 0.14 mg pancuronium in an infant weighing 1.34 kg.

Clinical and chemical correlates of the bilirubin-binding capacity in newborns.

• We correlated commonly measured clinical and chemical variables in sick neonates to the total bilirubin-binding capacity (TBBC) measured with the peroxidase method. The significant correlations related to the infants' maturity and degree of illness. The factors having the strongest relation to TBBC were Apgar scores, total plasma albumin and bilirubin levels, gestational age, birth weight, use of ventilatory assistance, and maternal general anesthesia. (Am J Dis Child1981;135:525-528)

Rapid Fluorometric Assay of Bilirubin and Bilirubin Binding Capacity in Blood of Jaundiced Neonates: Comparisons with Other Methods

The concentrations of total blood bilirubin, albumin-bound bilirubin, and the reserve and total bilirubin binding capacities of 35 neonatal blood samples (28 patients) were determined by automated front-face fluorometry ((hematofluorometer). These values were compared to results of diazo determinations, Sephadex gel filtration, and peroxidase-oxidation methods. Total blood bilirubin level by fluorometry agreed well with the total plasma bilirubin level by diazotization (r = .96, sigma = 1.7 mg/100 ml). Albumin-bound bilirubin concentrations by fluorometry also correlated well with diazo values (r = .95, sigma = 1.9 mg/100 ml) and were slightly lower than the total blood bilirubin concentrations. Values for total bilirubin binding capacity determined by fluorometry agreed well with results obtained for the same specimens by Sephadex gel filtration (n = 28, r = .97, sigma = 1.8 mg/100 ml) and by peroxidase-catalyzed oxidation (n = 25, r = .97, sigma = 1.7 mg/100 ml). The agreement among the results obtained by the three methods indicates a well-defined in vitro end point at which available primary or "tight" binding sites on albumin are saturated with bilirubin. In this clinical experience the coefficient of variation of results with the hematofluorometer was 8.4% for total blood bilirubin and 6.5% for total binding capacity. A comparison of "sick" with "well" infants revealed that the fraction of bilirubin not bound to albumin was significantly different for these two groups. The assays made with the hematofluorometer are quick (10 to 15 minutes) and require only a small quantity (approximately 150 microliters) of blood.

Reserve bilirubin binding capacity assessed by difference spectroscopy: Assay statistics and results on newborn sera

Bilirubin binding properties of newborn sera and assay parameters have been investigated using a difference spectroscopy procedure [9]. Reserve bilirubin binding capacity, serum bilirubin and the total bilirubin binding capacity can be determined using only 40 μl of serum. The measured total binding capacities agreed with the theoretical binding capacities calculated from serum albumin concentrations assuming a 1:1 molar binding ratio of bilirubin to albumin; in 102 assays on newborn sera, the ratio of experimental to theoretical total binding capacity was 1.04. Bilirubin binding capacity measurements were linear over the range 0–600 mg/1. Day to day precision of binding capacity determinations on 6 albumin controls yielded coefficients of variation between 4.1 and 7.2%. Recovery for the reserve bilirubin binding capacity determinations was 99.6%. In a study of 22 newborns, reserve bilirubin binding capacities showed an inverse relationship with the changes in serum bilirubin concentrations. None of the newborns included in our study appeared to be in danger of bilirubin encephalopathy.

Influence of gestational age and clinical status on bilirubin-binding capacity in newborn infants. Sephadex G-25 gel filtration technique.

Total bilirubin-binding capacity was measured by Sephadex G-25 gel filtration in 43 clinically well and 45 clinically ill newborn infants between 26 and 41 weeks' gestation. In the well patients, bilirubin-binding capacity, serum albumin concentration, and the molar-binding ratio of bilirubin to albumin were directly related to gestational age. In the sick patients, serum bilirubin-binding capacity and albumin concentration also correlated with gestational age; however, from 32 to 41 weeks' gestation, the mean values for the sick infants were significantly lower than for the well infants. In the sick infants, the molar binding ratio of bilirubin to albumin was also lower than in the well patients and did not correlate with gestational age. The data are in agreement with previous clinical findings indicating an increased risk for low-bilirubin kernicterus among immature infants and suggest that some critically ill term infants may be at risk for kernicterus at serum bilirubin levels below 20 mg/100 ml.

Effect of postnatal age and clinical status of newborn infants on bilirubin-binding capacity.

Serial determinations of bilirubin-binding capacity were performed in 61 newborn infants during the first 10 days of life. 27 infants were classified as term (gestational age greater than or equal to 36 weeks) and 34 as preterm (gestational age less than or equal to 33 weeks); 34 were classified as 'sick' and 27 as 'well'. Bilirubin-binding capacity was measured by Sephadex gel filtration. In relation to postnatal age, total bilirubin-binding capacity (TBBC) remained stable in well term and preterm infants, decreased slightly in sick preterm infants, and decreased significantly in sick term infants. TBBC, serum albumin, and molr binding ratio (B/A) were significantly higher in well than in sick infants in both term and preterm groups; there were no significant differences between sick term and sick preterm infants. Clinical recovery in 16 infants was associated with a significant rise in TBBC and in B/A. The data suggest that in healthy infants, the serum bilirubin-binding capacity remains relatively unchanged during the first 10 days of life. Clinically ill infants show wide patient-to-patient variability in TBBC. Because of the tendency of TBBC to decrease with postnatal age in sick infants, repeated determinations of TBBC may be indicated for the management of sick jaudiced newborns.

The lack of effect of phototherapy on serum bilirubin-binding capacity in newborn infants.

Using a Sephadex G-25 separation technique, the total bilirubin-binding capacity was measured in 18 jaundiced infants before and after phototherapy. The initial total bilirubin-binding capacity obtained at 20 to 113 hours of age averaged 17.5 +/- 4.4 mg/dl (mean +/- SD) and was unchanged during phototherapy at 34 to 135 hours of age. In ten infants, the total bilirubin-binding capacity was measured before, during, and 24 hours after the cessation of phototherapy. Here too, phototherapy did not significantly influence the TBBC. These data indicate that in vivo, phototherapy does not alter the serum bilirubin binding capacity of newborn infants.