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PubMed This is a summary of 20 peer-reviewed journal articles Updated
Obstetrics

The Science of the Diagnosis: Biology and Labs

At a Glance

Preeclampsia is diagnosed using a combination of blood pressure readings and lab tests that check organ health, such as urine protein, AST/ALT, and platelet counts. You do not need to have protein in your urine to be diagnosed if other severe features are present.

Understanding the biology of preeclampsia can help you make sense of why your doctor is ordering so many different tests. While it may feel like a series of unrelated checks, each lab provides a specific window into how your body—and your placenta—is functioning [1].

The Root Cause: The Placenta and Your Blood Vessels

Preeclampsia is fundamentally a condition of the placenta and the endothelium (the delicate inner lining of your blood vessels) [2].

  1. Placental Insufficiency: Early in pregnancy, the placenta’s blood vessels should widen to handle high blood flow. In preeclampsia, these vessels remain narrow, limiting the oxygen and nutrients the placenta receives [3].
  2. Endothelial Dysfunction: Because it isn’t getting enough oxygen, the placenta becomes “stressed” and releases proteins into your bloodstream [4]. These proteins travel through your body and irritate your blood vessel linings. This “irritation” causes your vessels to leak fluid (leading to swelling) and constrict (leading to high blood pressure) [5][6].

Why Proteinuria is No Longer “Required”

In the past, doctors believed you couldn’t have preeclampsia without proteinuria (protein in the urine). However, current guidelines from the American College of Obstetricians and Gynecologists (ACOG) have updated this [7].

We now know that preeclampsia can affect other organs, like the liver or brain, even before it affects the kidneys [8]. Today, you can be diagnosed with preeclampsia if you have new-onset high blood pressure plus either protein in your urine or other “severe features” like low platelets or liver issues [9].

Decoding Your Lab Report

Your medical team uses several key tests to monitor the severity of the condition:

Kidney Function Tests

  • Protein-to-Creatinine Ratio (PCR): A quick “spot” urine test that compares the amount of protein to waste (creatinine). It is often used instead of a 24-hour collection because it is faster and highly accurate [10][11].
  • 24-Hour Urine Collection: The “gold standard” where you collect all urine for a full day to measure exactly how much protein your kidneys are losing [12].
  • Serum Creatinine: A blood test that measures how well your kidneys are filtering waste. A level above 1.1 mg/dL can indicate kidney stress [8].

Liver and Blood Tests

  • AST and ALT (Liver Enzymes): When the liver is stressed by preeclampsia, these enzymes leak into the blood. Levels more than twice the normal range are considered a “severe feature” [13].
  • Platelet Count: Platelets help your blood clot. In severe preeclampsia, platelets can get “used up” or destroyed. A count below 100,000/μL (thrombocytopenia) is a serious warning sign [14][15].

The “Crystal Ball” Test: sFlt-1/PlGF Ratio

This newer blood test measures the balance between “pro-angiogenic” proteins (which help vessels grow) and “anti-angiogenic” proteins (which stress the vessels) [16].

  • What it means: A low ratio (typically 38 or less) is very good at “ruling out” the development of preeclampsia for the next week [17].
  • High ratios: Higher numbers (especially over 85 or 110 depending on the stage of pregnancy) suggest the placenta is under significant stress and the condition may progress soon [18][19].

Lab Completeness Checklist

When reviewing your care with your doctor, ensure these “big picture” markers have been checked recently:

  • [ ] Blood Pressure: Two readings of at least 140/90 [7].
  • [ ] Urine Protein: Either a PCR or 24-hour collection [10].
  • [ ] Platelets: To check for blood clotting health [14].
  • [ ] AST/ALT: To check for liver involvement [13].
  • [ ] Creatinine: To check for kidney health [8].
  • [ ] Angiogenic Ratio (sFlt-1/PlGF): To help predict progression (if available at your hospital) [20].

Back to Home

Common questions in this guide

Do I need to have protein in my urine to be diagnosed with preeclampsia?
No. Current guidelines state that you can be diagnosed with preeclampsia if you have new-onset high blood pressure along with other severe features, such as low platelets or liver issues, even without protein in your urine.
What does the sFlt-1/PlGF ratio test for in preeclampsia?
This blood test measures the balance of specific proteins that affect blood vessel health. A low ratio helps rule out the development of severe preeclampsia for the next week, while a high ratio suggests the placenta is under stress and the condition may progress.
Why are my liver enzymes (AST and ALT) being checked?
Preeclampsia can cause stress on your organs, including your liver. When the liver is stressed, AST and ALT enzymes leak into your bloodstream, and elevated levels are considered a severe warning sign that requires close monitoring.
What is a protein-to-creatinine ratio (PCR) test?
The PCR is a quick urine test that compares the amount of protein to a waste product called creatinine. It is frequently used instead of a 24-hour urine collection to quickly and accurately assess how well your kidneys are functioning.
Why is my doctor checking my platelet count?
Platelets are blood cells that help your blood clot. In severe preeclampsia, platelets can get used up or destroyed. A platelet count below 100,000 is a serious warning sign that requires immediate medical attention.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Is my preeclampsia being diagnosed based on protein in my urine, or other signs of organ dysfunction?
  2. 2.What was my sFlt-1/PlGF ratio, and how does that number help predict the next few weeks of my pregnancy?
  3. 3.Are my liver enzymes or platelet counts showing any signs of 'severe features'?
  4. 4.How often will we be repeating these lab tests to monitor for changes?
  5. 5.If my protein-to-creatinine ratio (PCR) is high but my blood pressure is stable, how does that change my care?

Questions For You

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Related questions

Preeclampsia Without Protein in Urine? | Inciteful MedWhat is the sFlt-1/PlGF Ratio Test? | Inciteful Med

References

References (20)
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    Analysis of ICAM-1 rs3093030, VCAM-1 rs3783605, and E-Selectin rs1805193 Polymorphisms in African Women Living with HIV and Preeclampsia.

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This page explains preeclampsia biology and diagnostic lab tests for educational purposes. Always consult your obstetrician or maternal-fetal medicine specialist to interpret your specific lab results.

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