Effect of long-term storage on placental growth factor and fms-like tyrosine kinase 1 measurements in samples from pregnant women.
OBJECTIVE
To assess the effect of storage time on the stability of placental growth factor (PlGF) and fms-like tyrosine kinase 1 (sFlt-1) levels in frozen serum samples from pregnant women.


METHODS
This is a matched case-control study using fresh and stored serum samples collected at 6, 12, 18, 24, 30 and 36 months prior to the collection of the fresh samples and frozen at -80°C. Forty-eight samples from each of the seven time-groups were matched for non-smoking Chinese, maternal weight, singleton-term pregnancy without major obstetric complications and extracted for PlGF and sFlt-1 assays. Multivariate analysis was performed to assess residual effects of the case-matching procedure. ANOVA was used to assess the effects of storage time.


RESULTS
Multivariate analysis of the 336 samples indicated that log(10)PlGF was positively correlated with parity (p=0.014) and gestational age (p=0.029), while log(10)sFlt-1 was inversely correlated with parity (p=0.018). After correcting for the residual effect of gestation and parity, ANOVA showed no significant difference in PlGF and sFlt-1 levels between the fresh samples and all stored samples (p=0.410 and p=0.158, respectively).


CONCLUSIONS
Serum PlGF and sFlt-1 levels are stable for at least 3 years when stored at -80°C. Parity is an independent factor of PlGF and sFlt-1 levels. PlGF levels are lower and sFlt-1 levels are higher in nulliparous women compared to multiparous.
Law
Lai Wa
LW
Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, SAR.
Sahota
Daljit Singh
DS
Chan
Lin Wai
LW
Chen
Min
M
Lau
Tze Kin
TK
Leung
Tak Yeung
TY
D000328:Adult; D001793:Blood Preservation / Q000379:methods*; D016022:Case-Control Studies; D015925:Cryopreservation; D004355:Drug Stability; D005260:Female; D006801:Humans; D015999:Multivariate Analysis; D010298:Parity; D000072483:Placenta Growth Factor; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000097:blood*; D013997:Time Factors; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000097:blood*
C000608036:PGF protein, human; D011257:Pregnancy Proteins; D000072483:Placenta Growth Factor; C501162:FLT1 protein, human; D040281:Vascular Endothelial Growth Factor Receptor-1