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Technical Briefs |
-Fetoprotein in Newborns
1
Istituto di Puericultura e Medicina Neonatale dell'Università di Genova, Servizio di Patologia Neonatale, Istituto G. Gaslini, 16146 Genova, Italy, and
2
Laboratorio Centrale di Analisi dell'istituto G. Gaslini, 16146 Genova, Italy;
a address correspondence to this author at: Istituto di Puericultura e Medicina Neonatale dell'Università di Genova, Istituto G. Gaslini, Largo G. Gaslini, 5, 16146 Genova, Italy
-Fetoprotein (AFP) is a single chain -globulin with a
molecular weight of ~70 000. AFP is produced in the developing fetus
by both the yolk sac and the fetal liver. At 12 weeks after conception
the yolk sac degenerates and the fetal liver becomes the main site of
synthesis. After 14 weeks of gestation (peak value of AFP), AFP
synthesis decreases until parturition (1). The observation
that AFP synthesis does not entirely cease at birth may be explained on
the basis of transient production sustained by the presence of fetal
hepatocytes (1). Very few, contradictory, and incomplete
data regarding the determination of reference values for AFP in healthy
newborns, correlated to birth weight (BW) and/or gestational age (GA),
are available (1)(2)(3)(4)(5)(6)(7). Yet the usefulness of serum AFP as a
diagnostic marker for the detection and/or differentiation of a great
number of infantile diseases is well established, especially for some
forms of malignant tumors and liver disorders
(8)(9).
Apparently healthy newborns (n = 150; 71 males and 79 females) admitted to our Neonatal Intensive Care Unit (Servizio di Patologia Neonatale, Università di Genova, Italia) were included in the study. Single capillary blood specimens were collected with parental consent within 24 h of birth, when blood collection for other clinical testing was carried out. All subjects were delivered naturally. Subjects who were delivered by cesarean section were excluded from the study. No relevant perinatal complications were present, and no evidence of hepatobiliary disease, cardiac disease, severe respiratory distress, infection, or congenital malformations was found. Six babies with conditions that had been associated previously with abnormal maternal plasma AFP concentrations were excluded. Five infants who developed severe hyaline membrane disease had plasma AFP concentrations that were similar to those of babies of the same GA who did not have this complication. No babies were delivered from diabetic mothers. Dexamethasone treatment administrated to the mothers of four babies before delivery to accelerate lung maturation did not appear to have a major effect on the early postnatal AFP concentration. In spite of this, these last two groups of patients were excluded. Infants at 30 weeks of gestation and those who weighed 1500 g or less were included in the study only if they were free of severe respiratory distress syndrome.
GA was calculated by the mother's estimated date of last menstrual period, by fetal ultrasonic evaluation, and by physical examination after birth (Dubowitz scoring system).
Serum AFP concentrations were determined by double antibody radioimmunoassay (Serono®) with a detection limit of 2 µg/L and an imprecision (CV) of 5.9% (18.6 ± 1.1 µg/L). The assay requires only 50 µL of blood. Because most of the infant serum specimens contained much higher AFP concentrations than adult samples, proper dilution was required before the assay.
Conventional statistical methods were applied to calculate the mean and
SD. The statistical significance of the difference between mean values
of subpopulations was evaluated by the Student t-test, with
a significance level defined at P = 0.05. Differences
in the means of multiple subpopulations were evaluated using ANOVA.
Changes of AFP concentrations with GA and BW, the x and
y variables representing AFP values in µg/L, BW in grams
(Fig. 1A
), and GA in weeks (Fig. 1B
), respectively, were evaluated by
regression analysis; the regression equations are shown in Fig. 1
.
|
BW values correlated significantly with GA. On the basis of correlation
analysis (r = 0.76; P <0.001) the babies
included in our study appeared to be of appropriate BW. No significant
difference was found between AFP values in males vs females (males,
n = 71, AFP = 151 ± 61 mg/L; females, n = 79,
AFP = 150 ± 59 mg/L). There was significant correlation
between AFP values and BW (r = 0.39; P
<0.001) and AFP and GA (r = 0.49; P
<0.001). Fig. 1
shows the regression of AFP concentration in our
patients vs BW and GA, as calculated by the equation. The 95%
confidence interval for each regression line is shown as dashed lines.
Several studies of AFP concentration in newborns have been carried out. Blair et al. (1) provided serum AFP reference values derived using logarithmic transformation of plasma AFP values and rearrangement against patient age corrected for GA deficit. Samples were obtained from 56 babies from birth to 5 months of age with various GAs. Serum AFP reference values in infancy were determined on the basis of mathematical correction of the data obtained.
Wu et al. (2) evaluated average health-related serum AFP concentrations at various ages in 32 healthy babies generically split into two different groups, premature and newborn, without further indication regarding GA and/or BW.
Mizejewski and co-workers (3)(4) studied serum AFP concentrations in newborns partitioned in two subgroups to distinguish small-for-gestational age (2500–2950 g) from premature (<2500 g) infants. The authors concluded that BW had to be considered the indicator of choice, whereas GA had to be avoided because its estimation was highly subjective.
Goraya et al. (5) provided plasma AFP values in preterm neonates. The authors included patients enrolled in the study belonging to four different groups, according to different GA and BW. This methodology failed to take into account the GA and the BW of each patient. Reference values were referred to the individual groups.
Obiekwe et al. (6) compared maternal and fetal AFP concentrations at term; they did not consider preterm infants. In fact, the lowest GA included in the study was 36 weeks. In addition, subjects from 36 to 39 weeks were considered as one single group. Obiekwe et al. (6) provided the sole observation regarding significant differences between AFP concentrations in males vs females, because AFP concentrations are considerably higher in males than in females.
Lee et al. (7) elaborated their data regarding serum AFP determination in a pediatric population ranging from newborn to children 12 months of age by using different and sophisticated statistical analysis. This study did not report definite values regarding GA and BW.
On the basis of these observations, we can conclude that, to date, reference values for AFP in healthy newborns at birth for both premature and full-term newborns are not well defined.
Our results demonstrate the following in our population: BW correlated significantly with GA; correlation analysis data (r = 0.76; P <0.001) suggested that all babies included in the study were of appropriate BW; there was no significant difference between AFP concentrations in males vs females; and there was significant correlation between AFP concentrations and BW (r = 0.39; P <0.001) and between AFP concentrations and GA (r = 0.49; P <0.001).
We conclude that the regression curves shown in Fig. 1
, which relate
AFP concentrations with BW and GA, may be used as a frame of reference
to assist the interpretation of AFP concentrations in newborn infants.
Footnotes
References
-fetoprotein reference ranges in infancy: effect of prematurity. Arch Dis Child 1987;62:362-369.
[Abstract]
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