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

Abstract

Background For pregnant women with suspected preeclampsia, the soluble fms-like tyrosine-kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio is a biomarker to aid diagnosis. We performed method comparisons between Elecsys® and Kryptor sFlt-1 and PlGF immunoassays and assessed the diagnostic performance for preeclampsia. Methods Serum samples from a case-control study involving 113 pregnant women with preeclampsia/elevated liver enzymes and low platelet count (HELLP) and 270 controls were analyzed. sFlt-1 and PlGF were measured using Roche Elecsys® and BRAHMS Kryptor sFlt-1/PlGF immunoassays. The sFlt-1/PlGF ratios were calculated, and Passing-Bablok regression/Bland-Altman plots were performed. Gestation-specific cut-offs, ≤33 and ≥85/≥110, were assessed. Results Mean (±2 standard deviation [SD]) differences between the 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, 151.74 (1085.11, -781.63). The Elecsys® and Kryptor immunoassays showed high correlation: Pearson's correlation coefficients were 0.913 (sFlt-1) and 0.945 (PlGF). Slopes were 1.06 (sFlt-1) and 0.79 (PlGF), resulting in ~20% lower values for Kryptor PlGF. Sensitivities and specificities using the sFlt-1/PlGF ≥85 cut-off for early-onset preeclampsia (20 + 0 to 33 + 6 weeks) were 88.1%/100.0% (Elecsys®) and 90.5%/96.2% (Kryptor), respectively, and using the ≥110 cut-off for late-onset preeclampsia (≥34 + 0 weeks) were 51.3%/96.5% (Elecsys®) and 78.9%/90.1% (Kryptor), respectively. Using Elecsys® and Kryptor sFlt-1/PlGF, 0% and 3.8% of women, respectively, were falsely ruled-in for early-onset, and 3.5% and 9.9%, respectively, for late-onset preeclampsia. Conclusions Despite high correlation between the Elecsys® and Kryptor immunoassays, we observed significant differences between sFlt-1/PlGF and PlGF results. Therefore, sFlt-1/PlGF cut-offs validated for Elecsys® immunoassays are not transferable to Kryptor immunoassays.

• Authors: Holger Stepan, Martin Hund, Peter Dilba, Johanna Sillman, Dietmar Schlembach
• Journal: Clinical chemistry and laboratory medicine (Clin Chem Lab Med) Vol. 57 Issue 9 Pg. 1339-1348 (08 27 2019) ISSN: 1437-4331 [Electronic] Germany
• PMID: 31323000 (Publication Type: Comparative Study, Journal Article)

Chemical References

• Biomarkers
• PGF protein, human
• Vascular Endothelial Growth Factor A
• Placenta Growth Factor
• FLT1 protein, human
• Vascular Endothelial Growth Factor Receptor-1

Topics

• Adult
• Algorithms
• Biomarkers (blood)
• Case-Control Studies
• Female
• Gestational Age
• HELLP Syndrome (diagnosis)
• Humans
• Immunoassay (methods)
• Placenta Growth Factor (analysis, blood, metabolism)
• Pre-Eclampsia (diagnosis, immunology)
• Pregnancy
• Research Design
• Sensitivity and Specificity
• Vascular Endothelial Growth Factor A (blood)
• Vascular Endothelial Growth Factor Receptor-1 (analysis, blood, metabolism)