What is the role of Congo red (CR) dye in the diagnosis of preeclampsia?

Updated: Nov 29, 2018
  • Author: Kee-Hak Lim, MD; Chief Editor: Ronald M Ramus, MD  more...
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A study at Yale University showed preliminary results suggesting that Congo red (CR), a dye currently used to locate atypical amyloid aggregates in Alzheimer disease, may also be effective in the early diagnosis of preeclampsia. [50] It was thought that this finding might lead to a spot urine test that could be used in emergency departments and internationally, especially in resource-poor countries where preeclampsia continues to be underdiagnosed and accounts for a large percentage of maternal and fetal mortality.

In a study of 40 pregnant women with severe preeclampsia and 40 healthy pregnant controls, Buhimschi et al found that the urine and placentas of women with preeclampsia contain aggregates of misfolded proteins. [52, 53] They suggested that urine CR spotting tests (CR binds to misfolded proteins) may be better than currently used current dipstick methods at diagnosing preeclampsia and indicating the need for medically indicated delivery. [52, 53]

In this study, a cutoff value of a 15% measure of redness on the CR spotting test had 100% sensitivity and 100% specificity for distinguishing women with severe preeclampsia from control subjects. [53] In a separate validation cohort of 563 pregnant women, the test had a sensitivity of 85.9%, a specificity of 85.0%, a positive likelihood ratio of 5.7, and a negative likelihood ratio of 0.17.

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