Correlation and precision of serum free bilirubin concentrations determined by single and two peroxidase concentration methods in term or late-preterm newborn infants using a FDA-approved analyzer.
BACKGROUND
Free bilirubin concentration (B(f)) is an index for identifying newborns at risk for developing bilirubin-induced neurotoxicity. It has been suggested that B(f) measured by a single peroxidase concentration (B(f-single)) does not equal the equilibrium concentration of B(f), which is confirmed by B(f) at two different peroxidase concentrations (B(f-two)). However, the differences between B(f-single) and B(f-two) are unknown in the serum of term or late-preterm newborn infants. Furthermore, to apply B(f-single) with savings on time and cost to the clinical setting, it is very important for us to clarify the differences between B(f-single) and B(f-two).


METHODS
Forty serum samples were obtained from 21 term or late-preterm newborns who were admitted at Kobe University Hospital. Using a peroxidase method, B(f-single) was measured at one peroxidase concentration, and B(f-two) was determined at two different peroxidase concentrations (the manufacturer's recommended peroxidase concentration and half the manufacturer's recommended peroxidase concentration). To clarify the relationship between B(f-single) and peroxidase concentrations, B(f-single) was measured at five different concentrations of peroxidase reagent. Intra-day and inter-day analyses were performed to assess the precision of B(f-single) and B(f-two).


RESULTS
1/B(f-single) increased as peroxidase concentration increased. B(f-single) was significantly lower than B(f-two) (B(f-single): 0.50 microg/dL [0.13 - 1.22 microg/dL] versus B(f-two): 0.59 microg/dL [0.15 - 1.76 microg/dL], p < 0.001), but B(f-single) was significantly correlated with B(f-two) (r = 0.953, p < 0.0001). Intra-day analysis showed that the CV was 9.7% for B(f-two) and 3.3% for B(f-single), and the inter-day CV was 12.4% for B(f-two) and 3.2% for B(f-single).


CONCLUSIONS
Although B(f-single) and B(f-two) are not identical, B(f-single) is significantly correlated with B(f-two) and it is more precise than B(f-two) in term or late-preterm newborns.
Department of Pediatrics, Kobe University Graduate School of Medicine, Japan.
Akihiro
A
Miwa
Ichiro
I
Morioka
Tomoyuki
T
Yokota
Akio
A
Shibata
Kiyomi
K
Matsuo
Kazumichi
K
Fujioka
Tsubasa
T
Koda
Satoru
S
Morikawa
Hisahide
H
Nishio
Naoki
N
Yokoyama
Hajime
H
Nakamura
Masafumi
M
Matsuo
Hideto
H
Yamada
D001663:Bilirubin / Q000097:blood* / Q000737:chemistry / Q000592:standards; D019937:Diagnostic Techniques and Procedures / Q000295:instrumentation* / Q000592:standards; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D007647:Kernicterus / Q000097:blood / Q000175:diagnosis; D008297:Male; D015997:Neonatal Screening / Q000295:instrumentation*; D010544:Peroxidases / Q000737:chemistry; D015203:Reproducibility of Results; D047929:Term Birth / Q000097:blood*; D014481:United States; D014486:United States Food and Drug Administration
D010544:Peroxidases; D001663:Bilirubin