Clinical usefulness of serum levels of soluble fms-like tyrosine kinase 1/placental growth factor ratio to rule out preeclampsia in women with new-onset lupus nephritis during pregnancy

Measurement of the soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio may be clinically useful to discriminate systemic lupus erythematosus (SLE) from preeclampsia. Here, we present a pregnant woman with new-onset SLE with hypertension, with the measurement of the sFlt-1/PlGF ratio during pregnancy. A 31-year-old Japanese nulliparous woman, who had been diagnosed with idiopathic thrombocytopenic purpura at 10 years, had a systolic blood pressure of 120 mmHg and was negative for proteinuria at 12⁺¹ weeks. Since her blood pressure increased to 159/86 mmHg with 3+ proteinuria at 25⁺⁴ weeks, preeclampsia was suspected. Deterioration of the kidney function (creatinine: 0.58 mg/dL at 24⁺⁶ weeks to 0.83 mg/dL at 33⁺⁶ weeks) necessitated cesarean section at 33⁺⁶ weeks. After delivery, she still showed increased creatinine and proteinuria. Therefore, she was transferred to a nephrology specialist in a tertiary center and was finally diagnosed with SLE with lupus nephritis class IV-G(A) (diffuse lupus nephritis). The serum levels of sFlt-1 and the sFlt-1/PlGF ratio, which are usually elevated in preeclampsia, were within normal reference ranges at 27⁺⁶, 28⁺¹, and 28⁺⁶ weeks of gestation, although the serum levels of PlGF were slightly lower than the normal reference range. In conclusion, measurement of the sFlt-1/PlGF ratio may be clinically useful to discriminate lupus nephritis from preeclampsia.