Urinary congophilia in pregnancy: a marker of kidney injury rather than preeclampsia.

Background: The differentiation between preeclampsia and similarly presenting kidney disease in pregnancy is a diagnostic challenge. Although some laboratory tests have been utilized, globally validated tools are yet needed, particularly in resource-limited settings. Congophilic proteins are abundantly detected in the urine of pregnant women who develop preeclampsia that is thought to be a marker of disease process. The present study aimed to assess the diagnostic and predictive utility of urinary congophilia in pregnant women with hypertensive disorders of pregnancy as well as kidney diseases.

Methods: This cohort study included 157 pregnant women, classified as healthy controls ( n  = 38), preeclampsia/eclampsia ( n  = 45), gestational hypertension ( n  = 9), chronic hypertension ( n  = 8), chronic kidney disease (CKD) ( n  = 27), and pregnancy-related acute kidney injury (PR-AKI) ( n  = 30). Urinary congophilia was assessed by Congo Red Dot Blot assay.

Results: Congo red retention (CRR) values were significantly higher in women with preeclampsia/eclampsia ( P  ≤ 0.001), chronic hypertension ( P  = 0.029), gestational hypertension ( P  = 0.017), CKD ( P  ≤ 0.001), PR-AKI secondary to preeclampsia ( P  ≤ 0.001), and PR-AKI secondary to other causes ( P  = 0.001), compared with healthy controls. Women with preeclampsia, CKD, and PR-AKI (non-preeclampsia related) exhibited the highest levels of CRR. CRR positively correlated to proteinuria ( P  = 0.006) and serum creatinine ( P  = 0.027). CRR did not significantly vary between women who presented antepartum and those presented postpartum after removal of the placenta ( P  = 0.707). CRR at a cut-off point of at least 1.272 had 91% specificity and 61.1% sensitivity in predicting renal recovery in PR-AKI patients. CRR had a poor specificity in discriminating preeclampsia from the other clinical presentations.

Conclusion: Urinary congophilia could not discriminate preeclampsia from similarly presenting kidney diseases in pregnancy. Further studies are needed to improve differentiation of these conditions.