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Variability of plasma cortisol levels in extremely low birth weight infants
P L Jett1, M H Samuels, P A McDaniel
1Department of Pediatrics, Oregon Health Sciences University, Portland 97201, USA.
Insights
Extremely low birth weight (ELBW) infants exhibit minimal plasma cortisol variability. A single random blood sample is sufficient for assessing adrenal function in these vulnerable newborns.
Area of Science:
- Endocrinology
- Neonatal Medicine
- Pediatric Physiology
Background:
- Cortisol secretion in children and adults follows a daily circadian rhythm with numerous fluctuations.
- Newborns, particularly extremely low birth weight (ELBW) infants, may present with adrenal insufficiency, necessitating reliable assessment methods.
- The absence of a clear circadian pattern in newborns complicates the timing of blood sampling for adrenal function tests.
Purpose of the Study:
- To characterize the pattern of plasma cortisol levels in extremely low birth weight (ELBW) infants.
- To determine if a single random cortisol measurement is adequate for assessing adrenal status in ELBW infants.
Main Methods:
- Blood specimens were collected every 20 minutes over a 6-hour period from 14 ELBW infants at 4-6 days of life.
- Plasma cortisol levels were analyzed, and statistical methods including cluster analysis and regression analysis were applied.
- Individual cortisol level variability was assessed using standard deviations from each infant's mean cortisol level.
Main Results:
- Plasma cortisol levels in ELBW infants showed minimal variation over the 6-hour sampling period, with low standard deviations from individual means.
- Cluster analysis revealed a low frequency of cortisol pulses (0.6 pulses/infant/6 hours).
- Regression analysis indicated minimal fluctuation in cortisol levels over time for each infant.
Conclusions:
- Extremely low birth weight infants demonstrate a stable pattern of plasma cortisol levels, unlike the typical pulsatile secretion seen in older individuals.
- A single, random plasma cortisol measurement is adequate for evaluating the adrenal status of ELBW infants.
- These findings simplify the diagnostic approach to potential adrenal insufficiency in ELBW neonates.
Abstract:
Cortisol is secreted by children and adults in a pulsatile pattern of 15-30 peaks and nadirs each day with a circadian rhythm. Newborns are known to lack the circadian pattern, leading to uncertainty about the appropriate time for blood sampling for assessment of adrenal function. Because extremely low birth weight (ELBW) infants may manifest signs of adrenal insufficiency, knowledge of the pattern of cortisol levels is necessary to guide the appropriate timing of blood sampling. To define the pattern of plasma cortisol levels in 14 ELBW infants, we obtained blood specimens every 20 min over a 6-h period at 4-6 days of life. Although cortisol levels in the 14 infants ranged from 2.0-54.5 micrograms/dL, each infant's cortisol levels varied little from his or her own mean cortisol level. The SDs calculated from each infant's mean cortisol level were small, ranging from 0.37-4.12 micrograms/dL. Cluster analysis was applied to the data; only 0.6 cortisol pulses/infant 6-h period were detected. Each infant's plasma cortisol levels were plotted against time, and regression analysis was performed. The slopes of the resulting lines of regression ranged from -0.0284 to 0.0221. Our data indicate that ELBW infants show little variability in their plasma cortisol levels over time; therefore, a single random measurement provides an adequate reflection of the adrenal status of the ELBW infant.