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Understanding Cardiac Troponin T in the Newborn Period

Vento and colleagues, in their recent article (1), report the use of air versus oxygen at newborn resuscitations. Troponins are widely used in adult medicine. However, since there are no accepted normal values in cord blood or in postnatal samples from healthy babies, it is difficult to use troponin values in newborns without expressing some caveats.

Several cohort studies have measured cord blood cardiac troponin T in healthy babies (2–4). All of these studies (a total of 1,150 babies) used the third-generation assay and reported a median value that is effectively the lower limit of the assay or undetectable (0.01 ng/ml). Two of the cord blood studies (2, 4) reported the 75th percentile as 0.014 ng/ml (n = 1,084) in healthy babies. Vento and coworkers (1) report a median value of 0.014 ng/ml. This could be due to different laboratory techniques, but the third-generation assay should be comparable across studies, as there is only one manufacturer. Alternatively, this result could be due to their sample size. Perhaps their laboratory needs to produce a larger reference range for comparison, or was there some other reason for the elevated troponin in the cord blood of their healthy babies? In their healthy controls, there is no postnatal rise in troponin values. Comparing 215 cord bloods with 113 postnatal samples in healthy babies showed a rise from 0.010 to 0.022 ng/ml by 68 h of age (5). The reason for this rise is unknown, but it seems to occur around 48 to 72 h (6) in healthy babies.

In their experimental groups, the cord values are higher than those in their control group. Troponin takes 2 to 4 h from insult to elevation in the blood. This is mainly from adult data with complete regional myocardial ischemia. It does raise the question of how long the babies had been asphyxiated prior to delivery? It is unusual that there are no reported cord pH values, as these would give further information on the degree of asphyxia in these babies. In addition, once myocardial damage has occurred, troponin levels take around 12 h to peak and then remain elevated for a significant time period. This is true in preterm infants as well as in adults (6). Therefore, I was surprised that the later troponin levels in the asphyxiated groups did not continue to rise more and that they were not compared with their respective cord values. There appears to be a numerical rise, but was there a statistically significant increase?

Simon J. Clark

Jessop Wing Neonatal Unit, Sheffield, United Kingdom

FOOTNOTES

Conflict of Interest Statement: S.J.C. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Vento M, Sastre J, Asensi MA, Viña J. Room-air resuscitation causes less damage to heart and kidney than 100% oxygen. Am J Respir Crit Care Med 2005;172:1393–1398.[Abstract/Free Full Text]
2. Clark SJ, Newland P, Yoxall CW, Subhedar NV. Cardiac troponin T in cord blood. Arch Dis Child 2001;84:F34–F37.
3. Mäkikallio K, Vuolteenaho O, Jouppila P, Räsänen J. Association of severe placental insufficiency and systemic venous pressure rise in the fetus with increased neonatal cardiac troponin T levels. Am J Obstet Gynecol 2000;183:726–731.[Medline]
4. Baum H, Hinze A, Bartels P, Neumeier D. Reference values for cardiac troponins T and I in healthy neonates. Clin Biochem 2004;37:1079–1082.[Medline]
5. Clark SJ, Newland P, Yoxall CW, Subhedar NV. Concentrations of cardiac troponin T in neonates with and without respiratory distress. Arch Dis Child 2004;89:F348–F352.
6. Clark SJ, Newland P, Yoxall CW, Subhedar NV. Sequential cardiac troponin T following delivery and its relationship with myocardial performance in neonates with respiratory distress syndrome. Eur J Pediatr 2006;165:87–93.[Medline]

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