Carboxyhemoglobin measurements in the diagnosis of ABO hemolytic disease

Role of Cord Blood Carboxyhemoglobin in Detecting Significant Hyperbilirubinemia in Term Neonates with ABO Alloimmunization

OBJECTIVE

This study aimed to assess whether cord blood carboxyhemoglobin (COHb) levels in jaundiced term neonates with and without a positive direct Coombs test (DCT) and in healthy controls could be used as a predictor of severe hyperbilirubinemia. The percentage of cord blood COHb should be higher among neonates with Coombs-positive ABO hemolytic disease than among those with Coombs-negative ABO incompatibility and higher than that of ABO-compatible control neonates.

STUDY DESIGN

This cross-sectional descriptive study of 198 term neonates comprised three subgroups: group I featured 68 DCT-positive ABO-incompatible neonates (ABO + DCT), group II featured 60 DCT-negative ABO-incompatible neonates with hyperbilirubinemia (ABO-DCT), and group III featured 70 healthy controls. COHb was determined by an OSM3 hemoximeter.

RESULTS

Group I differed from groups II and III for cord blood bilirubin, cord blood hemoglobin, and cord blood hematocrit. Groups I and II had higher mean total serum bilirubin (TSB) levels than group III, while there was no difference in the mean TSB levels between groups I and II. There was no significant difference between the COHb group means for groups I, II, and III (p = 0.98). The area under the receiver operating characteristic curve calculated for group I/group III and group II/group III were found to be 0.62 and 0.54, respectively.

CONCLUSION

COHb levels did not prove to be superior to the DCT for predicting the risk of developing severe hyperbilirubinemia in term neonates.

KEY POINTS

· COHb levels do not predict the risk of developing severe hyperbilirubinemia in term neonates.. · COHb levels may predict that ABO incompatibility in early life.. · COHb levels did not prove to be superior to the direct coombs test..

Clinical Factors Influencing Endogenous Carbon Monoxide Production and Carboxyhemoglobin Levels in Neonates

Carboxyhemoglobin (COHb) is an index of endogenous carbon monoxide formation during the hem degradation process and could be used to confirm hemolysis in neonates. The influence of other clinical factors on COHb values in neonates has not been fully investigated. We aimed to evaluate the influence of hemolysis, sepsis, respiratory distress, and postnatal age on COHb values. We retrospectively analyzed COHb measurements determined with a carbon monoxide-oximeter in 4 groups of term neonates: A-sepsis, B-respiratory distress, C-hemolysis, and D-healthy neonates. The mean COHb values were 1.41% (SD: 0.26), 1.32% (SD: 0.27), 2.5% (SD: 0.69), and 1.27% (SD: 0.19) (P<0.001) in groups A (n=8), B (n=37), C (n=16), and D (n=76), respectively. COHb in group C was significantly higher than in the other groups. There was a negative correlation between postnatal age and COHb in healthy neonates. A cut-off level of 1.7% had 93% (95% confidence interval [CI]: 89%-97%) sensitivity and 94% (95% CI: 90%-98%) specificity for diagnosis of hemolysis. COHb values were higher during the first days of life. We found that COHb levels in neonates with hemolysis were significantly higher and that the influence of sepsis and respiratory distress on COHb values was insignificant.

Elevated blood carboxyhemoglobin levels as an early predictor of phototherapy requirement in moderate and late preterm infants

Objective: Preterm infants are prone to increased bilirubin burden and display adverse outcomes if left unmonitored; therefore, predicting an increased bilirubin production is of paramount importance.Methods: We aimed to evaluate carboxyhemoglobin (COHb) levels in moderate (GA: 32^0/7-33^6/7) and late preterm (GA: 34^0/7-36^6/7) infants to assess whether this molecule could be used as an early predictor of phototherapy requirement.Results: A total of 221 infants were enrolled in the study. On admission, carboxyhemoglobin levels of infants who received phototherapy were significantly higher than that of infants who did not require this treatment, and this difference persisted in the consecutive hours (median (min-max): 1.2% (0.3-1.7) versus 0.8% (0.4-1.1); p < .001). The initial and consecutive COHb levels showed positive correlation (r = 0.77, p < .001). In the post-hoc analysis, direct antiglobulin test positivity significantly affected phototherapy requirement (p < .001). Receiver operating characteristics analysis showed that a COHb level of ≥0.95% was found to have a sensitivity of 90% and a specificity of 88%. Multinomial logistic regression analysis demonstrated that high COHb levels on admission significantly increased the likelihood of phototherapy requirement when adjusted for covariants (adjusted odds ratio: 2.2; 95% confidence interval: 1.4-3.5; p < .001).Conclusion: Carboxyhemoglobin measurement can be simply used to predict preterm infants who will require phototherapy.

The role of carboxyhemoglobin measured with CO-oximetry in the detection of hemolysis in newborns with ABO alloimmunization

OBJECTIVES

To evaluate carboxyhemoglobin (COHb) values measured with a CO-oximeter (Roche-cobas b 221) in jaundiced newborns with or without hemolysis and healthy controls in order to assess whether COHb measurement determined with a CO-oximeter could be used as an indicator of hemolysis in newborns with ABO alloimmunization.

METHODS

A total of 86 term newborn infants were prospectively studied. The study cohort consisted of three subgroups: 18 infants with ABO HDN, 21 infants with hyperbilirubinemia without hemolytic disease who required phototherapy, and 47 healthy controls. The COHb, bilirubin, and Hb levels were measured.

RESULTS

The three subgroups did not differ significantly with respect to birth weight, gestational age, gender, Apgar score, or mode of delivery. The ABO HDN infants had significantly higher COHb values than the healthy controls (median 2.4% versus 1.3%, p < 0.0005) and the group with hyperbilirubinemia without hemolytic disease (median 2.4% versus 1.3%, p < 0.0005), although the infants with hyperbilirubinemia without hemolytic disease did not have significantly higher COHb values compared with the healthy controls. The cut-off value of 1.7% COHb had 72% sensitivity and 97% specificity for confirming hemolysis in ABO alloimmunization.

CONCLUSIONS

Our data show that COHb values determined with CO-oximeters are higher in newborns with hemolysis than in those without hemolysis. COHb measured with CO-oximeters could be used to confirm hemolysis in infants with ABO alloimmunization.

Non-invasive measurements of carboxyhemoglobin and methemoglobin in children with sickle cell disease

Assessment of oxyhemoglobin saturation in patients with sickle cell disease (SCD) is vital for prompt recognition of hypoxemia. The accuracy of pulse oximeter measurements of blood oxygenation in SCD patients is variable, partially due to carboxyhemoglobin (COHb) and methemoglobin (MetHb), which decrease the oxygen content of blood. This study evaluated the accuracy and reliability of a non-invasive pulse co-oximeter in measuring COHb and MetHb percentages (SpCO and SpMet) in children with SCD. We hypothesized that measurements of COHb and MetHb by non-invasive pulse co-oximetry agree within acceptable clinical accuracy with those made by invasive whole blood co-oximetry. Fifty children with SCD-SS underwent pulse co-oximetry and blood co-oximetry while breathing room air. Non-invasive COHb and MetHb readings were compared to the corresponding blood measurements. The pulse co-oximeter bias was 0.1% for COHb and -0.22% for MetHb. The precision of the measured SpCO was ± 2.1% within a COHb range of 0.4-6.1%, and the precision of the measured SpMet was ± 0.33% within a MetHb range of 0.1-1.1%. Non-invasive pulse co-oximetry was useful in measuring COHb and MetHb levels in children with SCD. Although the non-invasive technique slightly overestimated the invasive COHb measurements and slightly underestimated the invasive MetHb measurements, there was close agreement between the two methods.

Hemolysis and hyperbilirubinemia in antiglobulin positive, direct ABO blood group heterospecific neonates

OBJECTIVE

We quantified hemolysis and determined the incidence of hyperbilirubinemia in neonates who were direct antiglobulin titer (DAT)-positive, ABO heterospecific, and compared variables among O-A and O-B subgroups.

STUDY DESIGN

Plasma total bilirubin (PTB) was determined before the neonates were discharged from the hospital and more frequently when clinically warranted, in neonates who were DAT positive with blood group A or B and with mothers who had blood group O. Heme catabolism (and therefore bilirubin production) was indexed by blood carboxyhemoglobin corrected for inspired carbon monoxide (COHbc). Hyperbilirubinemia was defined as any PTB concentration >95th percentile on the hour-of-life-specific bilirubin nomogram.

RESULTS

Of 164 neonates, 111 were O-A and 53 O-B. Overall, hyperbilirubinemia developed 85 neonates (51.8%), and it tended to be more prevalent in the O-B neonates than O-A neonates (62.3% versus 46.8%; P = .053). Hyperbilirubinemia developed in more O-B newborns than O-A newborns at <24 hours (93.9% versus 48.1%; P< .0001). COHbc values were globally higher than our previously published newborn values. Babies in whom hyperbilirubinemia developed had higher COHbc values than the already high values of babies who were non-hyperbilirubinemic, and O-B newborns tended to have higher values than their O-A counterparts.

CONCLUSIONS

DAT-positive, ABO heterospecificity is associated with increased hemolysis and a high incidence of neonatal hyperbilirubinemia. O-B heterospecificity tends to confer even higher risk than O-A counterparts.

Understanding severe hyperbilirubinemia and preventing kernicterus: Adjuncts in the interpretation of neonatal serum bilirubin

The serum total bilirubin concentration at any point in time represents the amount of bilirubin being produced minus that being excreted. Hyperbilirubinemia develops when bilirubin production exceeds the body's capacity to excrete it, primarily by conjugation. When extreme, hyperbilirubinemia may lead to the development of free bilirubin, that form of bilirubin which may cross the blood-brain barrier and enter and damage the basal nuclei of the brain. This rare, though devastating complication, may result in irreversible bilirubin induced brain damage termed kernicterus. In this paper, adjuncts to the interpretation of the serum total bilirubin are discussed, with the purpose of singling out those few neonates in real danger of bilirubin encephalopathy. Interpretation of the serum total bilirubin should be performed in conjunction with factors unique to the particular infant being evaluated. Understanding the mechanisms and dangers of severe neonatal hyperbilirubinemia should facilitate recognition of an emergency situation and optimize the speed with which bilirubin testing is performed and blood for exchange transfusion prepared. Hyperbilirubinemia is a condition of major importance and a source of concern to all involved in the management of the newborn. Its prevention and management should be based on the recently revised American Academy of Pediatric guidelines, with special attention paid to neonates manifesting risk factors for kernicterus. Close cooperation between the clinical laboratory and the medical team managing the newborn is an essential component in the management of a hyperbilirubinemic baby.

Neonatal hyperbilirubinemia in Japanese neonates: analysis of the heme oxygenase-1 gene and fetal hemoglobin composition in cord blood

Neonatal hyperbilirubinemia is frequent and severe in Japanese infants. Although the G71R mutation of the bilirubin uridine diphosphate-glucuronosyltransferase gene is associated with severe neonatal hyperbilirubinemia in this population, it accounts for only half of the neonates with severe hyperbilirubinemia. It was suggested that increased bilirubin production would also be associated with severe neonatal hyperbilirubinemia in Japanese infants. To elucidate the genetic factors causing severe hyperbilirubinemia in these patients, we studied two notable factors associated with bilirubin production: heme oxygenase-1, a key enzyme of heme metabolism, and fetal Hb composition, a factor possibly associated with heme load in neonates. We first determined the sequences of promoter and all coding regions of the heme oxygenase-1 gene in Japanese neonates who had undergone phototherapy, but found no mutation except for the polymorphic (GT)n repeats in the promoter region. These repeats modulate the transcription of the heme oxygenase-1 gene, and the longer repeat sequences are known to reduce the transcription. We detected a significant difference in the allele frequencies of each number of (GT)n repeats between Japanese and German populations. However, we could not find a relation between those polymorphisms and neonatal hyperbilirubinemia. We next analyzed the state of Hb switching of the gamma- to beta-globin chain and the phenotype of gamma-globin chain isoforms in cord blood. We found no relation between fetal Hb composition and neonatal hyperbilirubinemia. Further studies are required to elucidate genetic or environmental factors in neonatal hyperbilirubinemia in Japanese infants.

End-tidal carbon monoxide is predictive for neonatal non-hemolytic hyperbilirubinemia

BACKGROUND

The aim of the present study was to evaluate the value of an end-tidal carbon monoxide corrected for inhaled carbon monoxide concentration (ETCOc) at the early neonatal period. The value would be useful for predicting subsequent hyperbilirubinemia in non-hemolytic full-term infants.

METHODS

The ETCOc levels were measured every 6 h during the first 72 h of life in healthy, full-term, non-hemolytic, newborn Japanese infants using a breath carbon monoxide analyzer. The ETCOc levels in hyperbilirubinemic infants were compared with those in non-hyperbilirubinemic infants. Hyperbilirubinemia was defined as the level of the peak total serum bilirubin concentration (TBC) greater than or equal to 257 micromol/L (15.0 mg/dL). The ETCOc measurement for predicting subsequent hyperbilirubinemia was evaluated with a receiver-operating characteristic (ROC) curve.

RESULTS

Fifty-one infants were enrolled in the study. Seven of the 51 infants developed hyperbilirubinemia. The ETCOc levels in non-hyperbilirubinemic infants were decreased in the first 72 h after birth. However, those in the hyperbilirubinemic infants were not decreased significantly, and were higher than those in non-hyperbilirubinemic infants at 42, 48, 54 and 66 h of age. The ETCOc level at 42 h of age was the most predictive of subsequent hyperbilirubinemia by ROC analysis. At the cut-off level of 1.8 microL/L (p.p.m.), the sensitivity, the specificity, the positive predictive value and negative predictive value were 86, 80, 40 and 97%, respectively.

CONCLUSION

Increased ETCOc level in the early neonatal period is associated with subsequent hyperbilirubinemia, even in infants without hemolytic disease. The ETCOc measurement may be useful as a screening test for predicting hyperbilirubinemia without hemolytic diseases.

Zinc Protoporphyrin: A Metabolite with a Mission

Zinc protoporphyrin (ZnPP) is a normal metabolite that is formed in trace amounts during heme biosynthesis. The final reaction in the biosynthetic pathway of heme is the chelation of iron with protoporphyrin. During periods of iron insufficiency or impaired iron utilization, zinc becomes an alternative metal substrate for ferrochelatase, leading to increased ZnPP formation. Evidence suggests that this metal substitution is one of the first biochemical responses to iron depletion, causing increased ZnPP to appear in circulating erythrocytes. Because this zinc-for-iron substitution occurs predominantly within the bone marrow, the ZnPP/heme ratio in erythrocytes reflects iron status in the bone marrow. In addition, ZnPP may regulate heme catabolism through competitive inhibition of heme oxygenase, the rate-limiting enzyme in the heme degradation pathway that produces bilirubin and carbon monoxide. Physiological roles, especially relating to carbon monoxide and possibly nitric oxide production, have been suggested for ZnPP. Clinically, ZnPP quantification is valuable as a sensitive and specific tool for evaluating iron nutrition and metabolism. Diagnostic determinations are applicable in a variety of clinical settings, including pediatrics, obstetrics, and blood banking. ZnPP analytical methodologies for clinical studies are discussed. In addition to diagnostic tests and metabolic studies, ZnPP has a potential therapeutic application in controlling bilirubin formation in neonates as a preventive measure for hyperbilirubinemia. Biochemical research techniques, both in vivo and in vitro, are described for further studies into the role of ZnPP in metabolism and physiology.

Rhesus isoimmunization: increased hemolysis during early infancy

The objective of the present study was to determine whether whole blood carboxyhemoglobin (COHb) and plasma bilirubin, two indicators of hemolysis, are elevated in infants with severe Rh isoimmune hemolytic disease during the first months of life. Beginning at 2 wk of age and continuing monthly for 3 mo, serial blood samples were obtained for COHb, plasma bilirubin, Hb, reticulocyte count, plasma erythropoietin, plasma enzymes, and plasma iron. Because control infants (n = 13) and infants with ABO hemolytic disease (n = 5) did not differ from one another in any of the study parameters, these two groups were combined and compared with infants with the Rh isoimmunization. Infants with severe Rh isoimmune hemolytic disease (n = 13) were found to have significantly lower Hb and significantly higher bilirubin, the COHb fraction divided by the Hb concentration (COHb/Hb), and plasma erythropoietin levels at 2 and 6 wk of age, and reticulocyte counts at 6 wk. The remaining parameters were not different between the control-ABO group and Rh-isoimmune group at any of the study intervals. The study's two primary indicators of hemolysis, plasma bilirubin and COHb/Hb, were significantly correlated with one another in the Rh-immunized group (r = 0.66, p < 0.0001), but not in the combined control-ABO group. Serial Rh antibody concentrations measured in the serum of four neonates with Rh isoimmunization demonstrated a mean half-life of 14.3 d. We speculate that, among infants with severe Rh isoimmune hemolytic disease, elevated total bilirubin levels and COHb/Hb ratios identified in the early weeks of life indicate continuing hemolysis due to persistence of maternal Rh antibodies.

Intravenous immune globulin in neonatal immune hemolytic disease: does it reduce hemolysis?

We studied the effect of intravenous immune globulin (IVIG) on hemolysis in term, hyperbilirubinemic, Coomb's positive infants utilizing measurement of carboxyhemoglobin fraction corrected for inhaled carbon monoxide (COHbc), a sensitive indicator of hemolysis. COHbc values were determined before and after IVIG infusion. In those babies who responded with a decrease in serum total bilirubin (n = 19), no exchange transfusions were required and COHbc levels decreased significantly by 24 h post-IVIG from 1.37 +/- 0.31 to 1.12 +/- 0.26% tHb (p < 0.0001). There were no corresponding decreases in COHbc levels (1.989 +/- 0.54 to 1.82 +/- 0.48% tHb; p > 0.05) among those whose serum bilirubin levels did not decrease in response in to IVIG (n = 7), and all of these infants required exchange transfusions. Furthermore, the extent of the decrease in COHbc was related to the degree of decrease in serum bilirubin levels, such that the percentage decrease of bilirubin at 24 h was directly correlated with the percentage decrease of COHbc at 24 h (p = 0.007). We conclude that IVIG, when successful, inhibits hemolysis in these infants.