Clinical significance of Proteinuria during pregnancy
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Qualitative and/or quantitative measurement of urine protein excretion is one of the most common tests performed during pregnancy. For more than 100 years, proteinuria was necessary for the diagnosis of preeclampsia, but recent guidelines recommend that proteinuria is sufficient but not necessary for the diagnosis. Still, in clinical practice, the majority of patients with gestational hypertension will be diagnosed with preeclampsia based on the presence of proteinuria. While the reference standard for measuring urinary protein excretion is a 24-hour urine collection, spot urine protein creatinine ratio is a reasonable “rule-out” test for proteinuria. Urine dipstick screening for proteinuria does not provide any clinical benefit and should not be used to diagnose proteinuria. The classic cutoff cited to define proteinuria during pregnancy is a value >300 mg/24 hours or a urine protein creatinine ratio of at least 0.3. Using this cutoff the rate of isolated proteinuria in pregnancy may reach 8% whereas preeclampsia occurs among 3-8% of pregnancies. Although this threshold is widely accepted, its origin is not evidence-based on adverse pregnancy outcomes but rather on “expert” opinion and results of small studies.

After reviewing the available data, the most important factor that influences maternal and neonatal outcome is the severity of blood pressures and the presence of end-organ damage, rather than the excess protein excretion. Since the management of gestational hypertension and preeclampsia without severe features is almost identical in the frequency of surveillance and timing of delivery, the separation into two separate disorders is unnecessary. If the management of women with gestational hypertension with a positive assessment of proteinuria will not change, think urine assessment for proteinuria is unnecessary in women that develop new-onset blood pressure at or after 20 weeks of gestation. Furthermore, its not recommend repeated measurement of proteinuria for women with preeclampsia, the amount of proteinuria does not seem to be related to poor maternal and neonatal outcomes, and monitoring proteinuria may lead to un-indicated preterm deliveries and related neonatal complications.

Since the current diagnosis of preeclampsia in women with chronic kidney disease may be based on a change in protein excretion, a baseline protein excretion evaluation is critical in certain conditions such as chronic hypertension, diabetes, autoimmune, or other renal disorders. The current definition of superimposed preeclampsia possess a diagnostic dilemma and it is unclear whether a change in the baseline proteinuria reflects another systemic disease such as preeclampsia or whether women with chronic disease such as chronic hypertension or diabetes will experience a different “normal” pattern of protein excretion during pregnancy. Finally, limited data are available regarding angiogenic and other biomarkers in women with chronic kidney disease as a potential aid in distinguishing the worsening of baseline chronic kidney disease, chronic hypertension, from superimposed preeclampsia.

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