Eur J Pediatr (1991) 150: 271-273 034061999100036G

European Journal of

Pediatrics

9 Springer-Verlag 1991

First day serum creatine kinase B B isoenzyme in high-risk infants R. A. Primhak and E. Simmonds Department of Paediatrics, Children's Hospital, Western Bank, Sheffield $10 2TH, UK Received March 8, 1989 / Accepted May 14, 1990

Abstract. S e r u m c r e a t i n e k i n a s e B B ( C K - B B ) o n t h e 1st d a y o f life was m e a s u r e d b y r a d i o i m m u n o a s s a y in 37 v e r y low b i r t h w e i g h t ( V L B W ) infats, 14 s e v e r e l y asp h y x i a t e d infants a n d 24 c o n t r o l s . T h e 31 survivors f r o m t h e t w o h i g h - r i s k g r o u p s w e r e f o l l o w e d u p for 12 m o n t h s o r m o r e . V L B W n o n - s u r v i v o r s (n = 14) h a d significantly h i g h e r m e a n C K - B B levels t h a n survivors (n = 23), ( P < 0.05). H o w e v e r , if o n l y survivors w e r e c o n s i d e r e d , C K B B was a p o o r d i s c r i m i n a t o r o f o u t c o m e in e i t h e r s t u d y g r o u p . F i r s t d a y s e r u m C K - B B is n o t a useful p r e d i c t o r o f n e u r o d e v e l o p m e n t a l o u t c o m e in surviving h i g h - r i s k infants.

Key words: C r e a t i n e k i n a s e - A s p h y x i a - N e w b o r n in-

a 5-min Apgar score of 5 or less or signs of cerebral irritation in the 1st day of life, and were notified to the study within the 1st day of life. A control group of infants born unassisted by vertex vaginal delivery with Apgar scores of 7 or more at 1 and 5 rain was also studied. All infants were studied at the Jessop Hospital for Women, Sheffield with the informed consent of the parents and the approval of the District Ethical Committee.

Blood samples Arterial or venous blood was taken at a mean (+ SD) age of 9.8 + 3.6 h. The serum was separated by centrifugation within 20 min and stored at -70~ until analysis. Serum CK-BB was measured using the two-site RIA technique previously described [3].

fants

Follow-up

Introduction

A full neurological examination and a Ruth Griffiths developmental assessment were performed on all but two of the surviving highrisk infants at a corrected age of 12-24 months. A developmental quotient (DQ) was calculated based on age corrected for prematurity. Two children with severe neurological impairment did not have formal developmental assessment. Audiometry was performed using distraction testing and tympanometry where necessary. The outcome was graded as:

A m e t h o d for assessing t h e p r e s e n c e a n d s e v e r i t y of b r a i n i n j u r y in n e w b o r n infants is n e e d e d for p r o g n o s t i c p u r p o s e s as well as for t h e e v a l u a t i o n o f t e c h n i q u e s of int e r v e n t i o n in a s p h y x i a . O n e m e t h o d w h i c h has b e e n p r o p o s e d is t h e m e a s u r e m e n t o f t h e b r a i n - s p e c i f i c i s o e n z y m e o f c r e a t i n e - k i n a s e ( C K - B B ) in b l o o d [1, 9, 12] o r C S F [6]. M o s t studies h a v e u s e d an i m m u n o e l e c t r o p h o retie m e t h o d to m e a s u r e t h e i s o e n z y m e , w h i c h has a rela t i v e l y low sensitivity. W e h a v e s t u d i e d s e r u m C K - B B in n e w b o r n infants at high risk o f b r a i n i n j u r y using a sensitive t w o - s i t e m o n o c l o n a l a n t i b o d y r a d i o i m m u n o a s s a y (RIA) technique.

Materials and methods

Normal: DQ above 85 and no neurological abnormalities; Equivocal: DQ 75-85 or sensorineural deafness or equivocal neurological signs; Abnormal: DQ below 75 or definite neurological abnormalities. All follow up assessments were made without knowledge of the isoenzyme results.

Statistics In order to achieve an approximation of a normal distribution all enzyme results were transformed to natural logarithms prior to analysis. Differences between groups were tested for significance using Students's t-test with correction for small numbers, and categorical differences were assessed using Fisher's exact test.

Population Patients were included in the study if they were either very low birthweight (VLBW) (below 1500 g) or had asphyxia indicated by

Offprint requests to: R. A. Primhak Abbreviations: CK = creatine kinase; CSF = cerebrospinal fluid; DQ = developmental quotient; RIA = radioimmunoassay; VLBW = very low birth weight

Results A l t o g e t h e r 37 V L B W infants, 14 a s p h y x i a t e d infants a n d 24 c o n t r o l s w e r e s t u d i e d . T h e b i r t h weights, g e s t a t i o n a l ages a n d o u t c o m e s o f t h e V L B W a n d a s p h y x i a g r o u p s a r e s h o w n in T a b l e 1. T h e C K - B B levels a r e s h o w n for t h e d i f f e r e n t o u t c o m e g r o u p s in Fig. 1. I n the V L B W

272 Table 1. Birth weight, gestation and outcome of high-risk newborn

infants Asphyxia Number Birth weight (kg) (_+SD) Gestation (weeks) (-+ SD) CK-BB (geometric mean) (95% confidence limits) Normal outcome Equivocal outcome Abnormal outcome Dead

1000

14 2.71 _+0.86 36.9 +3.4 11.0 3.4, 35.9 4 2 2 6

VLBW

Control

37 1.11 +0.24 28.7 +3.0 6.8 4.1, 11.0 17 3 3 14

24 3.43 +0.35 39.6 +1.36 3.6 2.1, 6.2

-

0

:=L

o 100

9

-

in o X

0 9

O

t

o 0

00 10--

i

O9 9 o

I

X @9

1 --

tllX)O( Control

I ee~e~ Normal

~

I Equivocal

J

L 9 Abnormal

:

I

oo Dead

Fig.l. Serum CK-BB levels in asphyxiated (9 and VLBW (O) infants categorised by outcome, compared to 24 term control infants (• The upper 95% confidence interval derived from the control group is shown group mean values for non-survivors (13.3 gg/1, 95% confidence limits 6.7-26.3) were significantly higher than for survivors (4.5 gg/1, 95% confidence limits 2.4-8.3) (P < 0.05), but if only survivors were considered there was little discrimination of outcome in either study group.

The upper 95% confidence interval for the control infants was 32 gg/1, and if this is taken as the upper limit of normal then there was no non-random association between abnormal CK-BB level and outcome.

Discussion

Most previous studies in newborn infants have related death or acute neurological dysfunction to changes in serum or CSF CK-BB [1, 6]. Although two studies have found serum CK-BB to be a useful predictor of longerterm outcome in term asphyxia [2, 12], both have used death and neurological dysfunction as equivalent adverse outcomes, of which death was the more common. In the present study we studied CK-BB in serum rather than CSF because of the ethical difficulties of prospective CSF sampling and the greater potential clinical practicality of serum sampling. We used a single sample on the 1st day of life as this has been previously found to be more discriminant of asphyxia [10, 12]. In common with other workers [1, 12] we have assumed that there was no significant arteriovenous difference in CK-BB levels. The study design would not allow detection of all brain-injuring events, particularly in the VLBW group, but if serum CK-BB is a good reflection of brain injury then we would have expected that an abnormally high level would have been relatively specific for a poor outcome. However, poor outcome was not predictable from serum CK-BB in our study. The results of this study are at variance with previous studies in newborn infants [1, 10, 12]. This could be related to the use of a different technique for is 9 measurement. The two-site monoclonal antibody method used in the present study is the most sensitive and specific test available for the measurement of CK-BB [3]. In normal newborn infants the total serum CK rises two- or threefold [4] and in asphyxiated infants it may achieve levels of 10-30 times normal [8, 13]. Electrophoretic methods for estimation of CK-BB are based on calculations of fractional CK activity, and would be subject to magnification errors if the total CK were very high. It is possible that high CK-BB values in previous studies may have been in part a reflection of very high total CK activities, reflecting asphyxia per se rather than brain injury. Nevertheless, one recent study using electrophoretic techniques [9] has reported similar findings to ours. Although serum CK-BB measured by R I A has been shown to be elevated in adults with head injury [7] there is evidence that the blood-brain barrier is relatively impermeable to the is 9 [5]. CK-BB is found in tissues outside the nervous system [11] and it may be that in the asphyxiated newborn brain-derived CK-BB is masked in the serum by the larger contribution of other tissues. The findings of the present study suggest that an elevated serum CK-BB may be a predictor of mortality, but is not a useful indicator of brain injury.

Acknowledgements. We are most grateful to Dr. R. J. Thompson for performing the radioimmunoassays, to Mrs. S. Amos for technical assistance and to Trent Regional Health Authority for financialsupport.

273

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