Differentiating Systemic Lupus Erythematosus Flare From Preeclampsia in Pregnancy Using the Soluble Fms-Like Tyrosine Kinase-1/Placental Growth Factor Ratio

Systemic lupus erythematosus (SLE) may be exacerbated at any stage of pregnancy, complicating maternal and fetal outcomes. Additionally, pregnancies with SLE have a higher risk of preeclampsia (PE), requiring careful differentiation between SLE flare and PE when symptoms such as proteinuria emerge. We herein describe a 36-year-old pregnant woman with SLE who developed severe proteinuria (13 g/day) at 30 weeks of gestation without hypertension or thrombocytopenia. No abnormal urinary segments were observed. The differential diagnosis between SLE flare and the preliminary sign of PE was challenging. The soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) ratio was utilized for diagnostic clarification. A normal sFlt-1/PlGF ratio at 29+4 weeks of gestation suggested SLE flare rather than the preliminary sign of PE. Intensified immunosuppressive therapy with increased prednisolone (30 mg/day) attenuated proteinuria, allowing for late-term pregnancy. At 37+4 weeks of gestation, the patient developed late-onset PE with a hypertensive crisis, necessitating emergency cesarean delivery. The infant was delivered safely without complications. Postpartum recovery was uneventful, with stable maternal renal function. This case underscores the importance of angiogenic markers in distinguishing SLE flare from PE. An elevated sFlt-1/PlGF ratio is typically associated with PE, but not SLE flare, aiding in a differential diagnosis and guiding treatment strategies.