Procalcitonin in Cord Blood: Evaluating Reference Ranges in Healthy Newborns >32 Weeks Gestation

Abstract

This study was to determine the concentration of procalcitonin (PCT) in umbilical cord blood (UCB) in healthy newborns more than 32 weeks gestational age. A total of 82 newborns were enrolled in a cross-sectional study. UCB was collected and measured for PCT levels immediately after birth. As results, the mean gestational age and birth weight was 37.55 ± 2.33 weeks, 2891.46 ± 555.82 g, respectively. The median concentration of PCT in UCB in healthy newborns was 0.097 (IQR, 0.082-0.134) ng/ml. The concentration of PCT in UCB did not differ in gestational age, gender, method of delivery, birth weight, or risk factors for prolonged rupture of membranes and maternal fever at birth. This study establishes a reference range for PCT levels in UCB in healthy neonates more than 32 weeks gestation. This baseline data can support interpreting PCT levels and improve the early diagnosis of early-onset neonatal sepsis, and help minimize unnecessary antibiotic use in newborns.

Introduction

Procalcitonin (PCT) is a pro-hormone produced by thyroid C cells, as a precursor of calcitonin. ¹ Infection and/ or inflammation of the intrauterine environment results in an increase in the concentration of pro-inflammation cytokines, such as interleukin (IL)-1, IL-6, Tumor Necrosis Factor (TNF)-α. . ., in the plasma of the fetus, which is recognized as the fetal inflammatory response.^2,3 These proinflammatory cytokines along with endotoxins and cellular components such as peptidoglycan stimulate the fetus to secrete PCT.^1,3 After infection, PCT is secreted into the circulation. PCT mRNA can be detected in all tissues, ¹ which explains why extremely high concentrations of PCT (up to 100- to 1000-fold increase compared to physiological concentrations) can be produced. ¹

Compared with other markers, PCT has a higher specificity in response to systemic bacterial infection.^{4 -6} In infection, PCT levels increase early and can be detected within 2 hours, while C-reactive protein (CRP) begins to increase after about 6 hours. Interleukins can increase earlier, but their half-life is fast and the quantification technique is complicated, so they are rarely used in practice.^7,8 Due to its half-life, PCT levels typically decrease by about 50% per day when an infection is resolving. ⁷

There are several studies that have shown the role of umbilical cord blood (UCB) PCT as a biomarker in the diagnosis of early-onset neonatal sepsis (EOS).^{9 -11} Studies have shown that UCB PCT is increased in EOS compared to non-septic neonates.^9,10 However, the cut-off for diagnosing EOS is still not unified or has not been officially recommended by pediatric or neonatal associations. In addition, it is unclear whether PCT concentration in UCB is affected by maternal and fetal factors during labor. Currently, interpreting UCB PCT levels remains a concern. Therefore, we conducted this study with the aim of determining PCT concentration in healthy neonates more than 32 weeks of gestation and the influence of maternal and fetal factors on UCB PCT concentration.

Materials and Methods

Study Design

This is a cross-sectional study that was carried out at the Neonatal care unit and Obstetrics and Gynecology department of Hue University Hospital, between June 2023 and September 2024.

Participants

All healthy newborns >32 weeks of gestation.

Exclusion criteria: we excluded neonates who were transferred to another hospital during the early neonatal period, or neonates diagnosed with respiratory distress syndrome (RDS), EOS, congenital viral infection, or intraventricular hemorrhage.

Sample Size

A total of 82 healthy newborns at of beyond 32 weeks of gestation were selected in this study.

Variables and Measurements

Basic information of study group including gender, gestational age (GA), birth weight, type of delivery. Risk factors of EOS (maternal fever during labor, prolonged rupture of membranes, spontaneous preterm birth before 37 weeks, maternal infection with group B Streptococcus, maternal chorioamnionitis) according to the guidelines of the National Institute for Health and Care Excellence (NICE) 2021. ¹²

Neonates were monitored for at least 72 hours after birth to have clinical assessment morbidities and made sure to excluded EOS cases. Healthy neonates in this study included those who were asymptomatic (not hospitalized and clinically monitored for 72 hours after birth) and neonates with symptoms such as tachypnea (admitted and receiving both clinical and laboratory examination, including blood culture, complete blood count, and CRP), provided that they showed early symptom improvement within 48 hours, had normal laboratory results, and were ruled out for EOS. No neonates with RDS were present in the study group. During the study period, we collected 129 UCB PCT samples. We excluded 47 of cases, including: 3 cases transferred to another hospital and 44 cases with other diseases (RDS, EOS, congenital viral infection, intraventricular hemorrhage).

PCT laboratory test: 2 ml of umbilical cord venous blood was collected by needle immediately after cutting the umbilical cord into a sterile test tube containing lithium heparin and transferred to the laboratory. Measurement of PCT level was performed at the Laboratory Department of Hospital. The results was analyzed by the COBAS^® 6000/8000 (ROCHE DIAGNOSTICS, Japan.

Statistical Analysis

Qualitative variables were presented as frequencies and proportions. Continuous variables were presented as medians, interquartile if its non-normally distributed or means, standard deviation if its normally distributed. To differentiate for 2 groups, Mann-Whitney test was applied. Data were analyzed using SPSS 20.0 software. P < .05 was considered to indicate statistical significance.

Ethical Statements

This study was ethically approved by the Biomedical Ethics Committee of University of Medicine and Pharmacy, Hue University (Code: H2023/195, dated May 24, 2023).

Results

This study included 82 healthy newborns beyond 32 weeks of gestation. Our results showed that preterm newborns from 32 to <37 weeks accounted for 32.9%, term newborns accounted for 67.1%, the average GA and birth weight of the study group were 37.55 ± 2.33 weeks of gestation and 2891.46 ± 555.82 g, respectively. Male newborns accounted for 56.1%. The proportion of cesarean sections and vaginal deliveries was similar (Table 1).

Table 1.

Characteristics of Study Population.

Characteristics		N = 82(%)
Gestational age(weeks)	32–<34	4 (4.9)
	34–<37	23 (28.0)
	37–<42	55 (67.1)
	Mean ± SD	37.55 ± 2.33
	Min-max	32–41
Sex	Male	46 (56.1)
	Female	36 (43.9)
Type of delivery	Cesarean section	42 (51.2)
	Vaginal	40 (48.8)
Birth weight (g)	<2500 g	20 (24.4)
	≥2500 g	62 (75.6)
	Mean ± SD	2891.46 ± 555.82
	Min-max	1400–4200

The median UCB PCT concentration in healthy newborns was 0.097 (0.082-0.134) ng/ml. In preterm newborns (32-<37 weeks), the median PCT was 0.095 (0.078-0.133) ng/ml, while in term newborns the median PCT was 0.098 (0.082-0.137) ng/ml. The median concentration of PCT in UCB in low birth weight (LBW) neonates was 0.1005 (0.083-0.139) ng/ml. There were no significant differences in UCB PCT concentration in healthy newborns according to GA, gender, method of delivery, or birth weight (P > .05; Table 2).

Table 2.

PCT Concentration in Umbilical Cord Blood in Healthy Neonates.

Variables		n	Median PCT (ng/ml)	IQR (ng/ml)	Range (ng/ml)	P-value
Gestational age (weeks)	<37	27	0.095	0.078–0.133	0.037–0.207	.601
	≥37-42	55	0.098	0.082–0.137	0.02–0.323
Sex	Male	46	0.095	0.084–0.133	0.02–0.254	.779
	Female	36	0.099	0.078–0.140	0.032–0.323
Types of delivery	Cesarean section	42	0.100	0.079–0.152	0.02–0.254	.606
	Vaginal	40	0.094	0.083–0.124	0.032–0.323
Birth weight	<2500 g	20	0.1005	0.0835–0.139	0.038–0.207	.646
	≥2500 g	62	0.096	0.079–0.133	0.02–0.323
Prelabor rupture of membranes	≥18 hours	8	0.102	0.087–0.145	0.066–0.207	.611
	<18 hours	74	0.097	0.079–0.134	0.02–0.323
Intrapartum fever higher than 38°C	Yes	14	0.121	0.086–0.144	0.02–0.323	.321
	No	68	0.096	0.080–0.133	0.032–0.254
Total population		82	0.097	0.082–0.134	0.02–0.323	–

Abbreviation: PCT, procalcitonin.

In healthy newborns with risk factors for EOS, such as prolonged ruptured membranes more than 18 hours, or maternal fever during labor, the median concentration of PCT in UCB was higher than that in healthy newborns without these risk factors, but the difference was not statistically significant (P > .05). In addition, our study recorded 1 case of chorioamnionitis and 1 case of maternal group B Streptococcus infection. However, due to the limited number of cases in these 2 groups, we did not analyze the median value of PCT (Table 2).

Discussion

PCT is a sensitive marker of bacterial infection, with rapid physiological changes in the first few days after birth^1,13 and kinetic differences for preterm neonates with delayed peak and prolonged return to its physiological baseline. ¹³ Therefore, analysis of UCB PCT concentrations would be earlier and more valuable than postnatal PCT values. In this study, we selected only healthy newborns, therefore, the study group consisted of moderate and late preterm and term neonates (more than 32 weeks of gestation). Previous studies have also suggested that PCT may also be triggered by other perinatal conditions, such as intracranial hemorrhage and hypoxic ischemic encephalopathy. ¹⁴ Therefore, the newborns in our study did not have EOS, asphyxia or other conditions that require specific treatment in the early neonatal period.

Bianco et al showed that very preterm neonates (less than 32 weeks of gestation), had higher UCB PCT concentration than term neonates, even there was no EOS in these newborns, because they could have more pathological conditions. ¹¹ This study also reported that the average value of PCT in UCB was 0.32 ng/ml. ¹¹ For extremely preterm neonates (less than 28 weeks of gestation), Frerot et al found that the UCB PCT concentration was even higher. ¹⁰ Some previous studies have suggested that very preterm and extremely preterm neonates often have respiratory failure and hypoxemia, which may be factors that increase PCT production. ¹⁵ Therefore, our study was only performed on newborns more than 32 weeks, with an average GA of 37.55 ± 2.33 weeks, and the risk of pathology was reduced. Our results showed that the median value of PCT in the group of preterm newborns (32-<37 weeks) and the group of term newborns (>37 weeks) were similar, with no statistically significant difference.

The median concentration of PCT in UCB in whole group was 0.0975 (0.082-0.134) ng/ml, and the median PCT in preterm group was 0.095 (0.078-0.133) ng/ml, while the median PCT in term group was 0.098 (0.082-0.137) ng/ml. Tran et al (2022) also had similar result, with the median PCT concentration in the non-EOS group being 0.087 ng/ml. ¹⁶ On the other hand, Joram et al showed that the median cord PCT value in the group of non-infected neonates was 0.16 ng/ml, ⁹ higher than that in our study. This difference could be explained by the fact that Joram’s study included neonates in all GA. Furthermore, multivariate analysis in this study demonstrated that neonates with GA <28 weeks, and 28-<32 weeks were associated with increased UCB PCT concentrations, while the group of preterm neonates (32-36 weeks) did not relate to increase PCT levels. ⁹ Similarly, this study found that birth weight <1000 g, and 1001-<1500 g were related to increased UCB PCT levels, while birth weight 1501 to 2500 g had no significant effect on PCT levels. ⁹ Our study did not find a statistically significant difference in PCT levels between both groups (above and below 2500 g).

We investigated whether UCB PCT concentrations are affected by the risk factors for EOS? In our study, there were some newborns at maternal risk factors of infection such as spontaneous preterm birth before 37 weeks, maternal fever, and prolonged rupture of membranes. Although maternal infections can increase the risk of EOS, we carefully followed up the neonates in the early postnatal period and excluded any cases of EOS. Our results showed that above risk factors did not affect the PCT concentration in healthy neonates. Joram et al also reported that multiple pregnancy, birth asphyxia, and intrauterine growth retardation did not affect the PCT levels. ⁹ In contrast, Frerot et al studied extremely preterm neonates (less than 28 weeks of gestation) found that clinical chorioamnionitis in mothers was associated with increased PCT concentration > 0.5 μg/L (OR 2.58; 95% CI: 1.35-4.94; p = 0.004). ¹⁰

The use of UCB as an alternative source for tests from peripheral venous blood to minimize pain and blood loss for newborns is increasingly being studied and applied. ¹⁷ The results showed that UCB PCT concentrations in healthy neonates beyond 32 weeks of gestation were not affected by perinatal factors, de-monstrating the independence and stability of UCB PCT. Furthermore, previous study reported that PCT levels increases significantly in special conditions, particularly EOS.^9,16 In addition, our findings in neonates with risk factors for EOS but absence of clinical symptoms suggested that the interpretation of UCB PCT values or other biological tests should be integrated with a comprehensive clinical assessment. Therefore, we should be more carefully in initiating empirical antibiotic therapy for newborns with only risk factors and no clinical symptoms, as is currently practiced in many neonatal units. The results of our study help to better understand the concentration of PCT in UCB in healthy neonates >32 weeks, thereby helping to better analysis of cases of EOS, and limiting the use of unnecessary antibiotics. On the other hand, our study only collected UCB PCT values and followed clinical outcomes during the first 72 hours, therefore, future studies assessing the dynamic changes of PCT in healthy neonates during the postnatal days are needed. This would allow for better clinical applicability by incorporating longitudinal PCT data for analysis and evaluating the diagnosis of neonatal EOS.

Conclusions

This study establishes a reference range for PCT levels in UCB in healthy neonates more than 32 weeks gestation. In these healthy newborns, UCB PCT concentrations were not affected by GA, gender, mode of delivery, birth weight, and maternal risk factors for EOS.