205. Elecsys® and Kryptor immunoassays for the measurement of sFlt-1 and PlGF to aid preeclampsia diagnosis: Are they comparable?

Abstract

Introduction In pregnant women with suspected preeclampsia, the soluble Fms-like tyrosine-kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio is used as a biomarker to aid diagnosis. sFlt-1 and PlGF levels are measured using Elecsys® (Roche) or Kryptor (BRAHMS) immunoassays; Elecsys® sFlt-1/PlGF ratio cut-offs 85 and 110 may indicate preeclampsia. Objectives To perform method comparisons between the Elecsys® versus Kryptor immunoassays for sFlt-1 and PlGF measurement, and assess diagnostic performance for preeclampsia/HELLP syndrome in a large cohort. Methods Analyses included 396 serum samples from a case-control study in 113 pregnant women with preeclampsia or HELLP syndrome and 270 controls. sFlt-1 and PlGF were determined using Elecsys® and Kryptor sFlt-1 and PlGF immunoassays, and gestation-specific cut-offs 85 for early-onset preeclampsia (eoPE; 20 + 0–33 + 6 weeks) and 110 for late-onset preeclampsia (loPE; ⩾34 + 0 weeks) were assessed. Method comparisons were based on Passing-Bablok regression, and Bland–Altman plots (CLSI EP09-A3). ROC analysis was performed for all sFlt-1/PlGF cut-offs. Results Mean (±2 SD) differences between Elecsys® and Kryptor values were: sFlt-1, 173.13 pg/mL (6237.66, −5891.40); PlGF, 102.71 pg/mL (186.06, −391.48); and sFlt-1/PlGF ratio, 151.74 (1085.11, −781.63). Elecsys® and Kryptor immunoassays showed high correlation: Pearson’s correlation coefficient (r), 0.913; slope, 1.06; intercept, −358.19 pg/mL (sFlt-1), and Pearson’s r, 0.945; slope, 0.79; intercept, −17.89 pg/mL (PlGF), resulting in ∼20% lower values for PlGF. Sensitivities and specificities using the sFlt-1/PlGF 85 cut-off (eoPE) were 88.0%/100.0% (Elecsys®) and 90.4%/96.2% (Kryptor), and using a sFlt-1/PlGF 110 cut-off (loPE) were 51.3%/96.5% (Elecsys®) and 78.9%/90.1% (Kryptor). Using Elecsys® and Kryptor sFlt-1/PlGF ratios, 0% and 3.8% of women were falsely ruled-in for eoPE, and 3.5% and 9.9% for loPE. Discussion Despite high correlation between Elecsys® and Kryptor immunoassays, substantial differences were observed between Elecsys® and Kryptor sFlt-1/PlGF and PlGF. sFlt-1/PlGF cut-offs 85 and 110 showed lower specificity on Kryptor versus Elecsys®, resulting in more false-positive preeclampsia diagnoses.