Preeclampsia is diagnosed when a pregnant woman develops new high blood pressure after 20 weeks of gestation, confirmed by two elevated readings at least 4 hours apart, along with signs of organ stress such as protein in the urine or abnormal blood work. There is no single test for preeclampsia. Instead, the diagnosis relies on a combination of blood pressure measurements, urine tests, and lab work that together reveal how the condition is affecting the body.
Blood Pressure Thresholds
The first and most essential piece of the diagnosis is elevated blood pressure. A systolic reading (the top number) of 140 mmHg or higher, or a diastolic reading (the bottom number) of 90 mmHg or higher, meets the threshold. Crucially, this has to be a new finding in someone who previously had normal blood pressure during pregnancy. A single high reading isn’t enough on its own: two elevated readings taken more than 4 hours apart are required to confirm the pattern.
There’s one exception to the waiting period. If blood pressure is severely elevated, with a systolic of 160 or higher or a diastolic of 110 or higher, the diagnosis can be confirmed much more quickly so that treatment can begin right away.
The Role of Urine Testing
Protein in the urine has long been considered a hallmark of preeclampsia, and it remains a key part of the diagnostic workup. The gold standard is a 24-hour urine collection showing 300 mg or more of protein. Because collecting urine for a full day isn’t always practical, a spot urine test that calculates the protein-to-creatinine ratio can be used instead; a ratio of 0.3 or higher is considered positive. A simple dipstick reading of 1+ also counts, though it’s considered less reliable and is only used when the more precise methods aren’t available.
What many people don’t realize is that proteinuria is no longer required for a preeclampsia diagnosis. If you have new-onset high blood pressure plus evidence that other organs are being affected, that’s enough.
Diagnosis Without Protein in the Urine
Current guidelines from the American College of Obstetricians and Gynecologists (ACOG) recognize that preeclampsia can damage organs well before protein shows up in the urine. When proteinuria is absent, the diagnosis can still be made if new-onset high blood pressure is accompanied by any one of the following:
- Low platelet count: a drop below 100,000 per microliter, which signals the blood’s clotting system is being disrupted
- Kidney problems: indicated by a creatinine level of 1.1 mg/dL or higher, or a level that has doubled from your baseline
- Liver dysfunction: liver enzymes rising to more than twice their normal upper limit
- Fluid in the lungs (pulmonary edema)
- New-onset headache or visual changes that can’t be explained by another cause and don’t respond to medication
This broader definition matters because it catches cases that older diagnostic criteria would have missed entirely.
What Symptoms Prompt Testing
Many cases of preeclampsia are first flagged during a routine prenatal visit when a blood pressure reading comes back high. But certain symptoms can also trigger a closer look. The most common complaint is a new headache that feels different from typical pregnancy headaches and doesn’t improve with over-the-counter pain relief. This may come with visual disturbances like blurriness, seeing spots, or light sensitivity.
Pain in the upper right side of the abdomen or just below the breastbone, sometimes with nausea or vomiting, points toward liver involvement. Shortness of breath that’s worsening beyond what you’d expect in pregnancy can signal fluid buildup in the lungs. Swelling, particularly in the face or hands (rather than the feet and ankles, which swell in most pregnancies), is another red flag that prompts further evaluation.
Preeclampsia With Severe Features
Once preeclampsia is diagnosed, the next step is determining whether it has severe features, because this changes how urgently it needs to be managed. Blood pressure of 160/110 mmHg or higher automatically qualifies as severe, regardless of what other tests show. Beyond that, any of the organ-damage findings listed above, including a platelet count below 100,000, liver enzymes more than double the normal limit, kidney impairment, pulmonary edema, or persistent neurological symptoms, elevates the diagnosis to preeclampsia with severe features.
The distinction is not just academic. Preeclampsia without severe features may be monitored closely with the goal of reaching a safer gestational age for delivery. Preeclampsia with severe features typically moves the timeline up significantly, because the risks of continuing the pregnancy begin to outweigh the benefits.
Blood Tests That May Help Predict Risk
A newer type of blood test measures the ratio of two proteins in the bloodstream that reflect how well the placenta is functioning. In women who already have high blood pressure, this ratio can help predict whether preeclampsia will develop within the next week. Research in a large cohort found that a ratio of 74 or higher predicted early-onset preeclampsia (before 34 weeks) with about 88% sensitivity and 97% specificity, meaning it catches most true cases while rarely producing false alarms. For later-onset disease, a higher cutoff of 95 was used, though it was less sensitive at picking up every case.
This blood test is not yet a standard part of diagnosis everywhere, but it’s increasingly being used as a risk-stratification tool, especially in cases where the clinical picture is uncertain.
Postpartum Preeclampsia
Preeclampsia doesn’t always appear before delivery. New-onset high blood pressure developing between 48 hours and 6 weeks after giving birth should raise suspicion for postpartum preeclampsia. The blood pressure thresholds are the same as during pregnancy: 140/90 mmHg or higher. However, experts place less emphasis on proteinuria in the postpartum setting, because there’s no evidence that protein in the urine helps predict outcomes or distinguish between types of postpartum hypertension.
The presence of any severe feature, including severely elevated blood pressure in a woman with no prior history of hypertension, is generally treated as postpartum preeclampsia after other potential causes have been ruled out. This is worth knowing because many new parents don’t expect a pregnancy complication to appear after the baby has already arrived, and symptoms like severe headaches or vision changes in the days or weeks following birth deserve prompt attention.