Preeclampsia is diagnosed through a combination of blood pressure readings, urine tests, and blood work, typically starting after 20 weeks of pregnancy. The key threshold is a blood pressure of 140/90 mmHg or higher on two separate readings at least four hours apart. From there, your provider runs additional tests to confirm the diagnosis and assess severity.
Blood Pressure: The First Signal
Blood pressure measurement is the starting point for every preeclampsia evaluation. Two readings of 140 mmHg systolic or 90 mmHg diastolic (or both), taken at least four hours apart, meet the initial criteria. These readings must occur after 20 weeks of pregnancy in someone whose blood pressure was previously normal.
If your blood pressure hits the severe range, 160 mmHg systolic or 110 mmHg diastolic, the four-hour waiting period isn’t necessary. A single confirmed reading at that level, combined with any other concerning finding, is enough for a diagnosis of preeclampsia with severe features.
It’s worth knowing that high blood pressure alone, without protein in the urine or other organ involvement, is classified as gestational hypertension rather than preeclampsia. The distinction matters because gestational hypertension carries a different risk profile. But if lab results or symptoms point to organ stress, the diagnosis shifts to preeclampsia even without proteinuria.
Urine Tests for Protein
Protein spilling into your urine is one of the hallmark signs of preeclampsia. It signals that the kidneys are under stress. There are three ways to measure it, and your provider will choose based on what’s practical and how quickly results are needed.
- 24-hour urine collection: You collect all urine over a full day. A total of 300 mg of protein or more confirms significant proteinuria. This is considered the traditional standard, but it’s slow and inconvenient.
- Spot urine protein-to-creatinine ratio: A single urine sample is tested for both protein and creatinine, and the ratio is calculated. A result of 0.3 or higher is the diagnostic cutoff. This method gives results much faster and correlates well with the 24-hour collection, making it the more common choice in practice.
- Urine dipstick: A quick in-office test where a treated strip is dipped into a urine sample. A reading of 2+ or higher raises concern, but this method is the least precise. It’s typically used only when the other options aren’t immediately available.
Proteinuria has long been considered a core requirement for diagnosing preeclampsia, but it isn’t always present. You can be diagnosed without it if blood work or symptoms show that other organs are affected.
Blood Tests That Reveal Organ Stress
A set of blood tests rounds out the diagnostic picture. These check whether preeclampsia is affecting your liver, kidneys, or blood cells.
Liver enzymes (AST and ALT) are measured to detect liver inflammation or damage. In preeclampsia, these values rise above twice the normal upper limit. Your provider will also check your platelet count. Healthy platelets fall between 150,000 and 400,000 per microliter. A drop below 100,000 is a serious finding and one of the criteria that can confirm preeclampsia even without protein in the urine.
Kidney function is assessed through serum creatinine. A level above 1.1 mg/dL, or a doubling from your baseline, indicates the kidneys aren’t filtering properly. In severe forms like HELLP syndrome, red blood cells can actually be damaged or destroyed, causing a specific type of anemia that shows up on a blood smear.
These blood tests aren’t one-time checks. If your provider suspects preeclampsia, they’ll repeat them to track whether the condition is stable or worsening.
The Physical Exam
Beyond numbers on a lab report, your provider looks for physical signs during the exam. Swelling is common in pregnancy, but the type of swelling matters. Puffiness in the face or hands (the kind where a ring suddenly doesn’t fit) is more concerning than swollen ankles, which are common and usually harmless. Sudden weight gain of more than five pounds in a week can also be a red flag.
Providers check reflexes because exaggerated responses, called hyperreflexia, suggest the nervous system is being affected. They’ll press on the upper right side of your abdomen to check for liver tenderness and listen to your lungs for signs of fluid buildup. These physical findings help determine whether the condition has progressed to severe features.
What Makes It “Severe”
Preeclampsia exists on a spectrum, and the distinction between mild and severe changes how urgently it’s managed. A diagnosis of preeclampsia with severe features is made when any of the following are present alongside elevated blood pressure:
- Blood pressure at or above 160/110 mmHg
- Platelet count below 100,000
- Liver enzymes more than twice the normal upper limit
- Serum creatinine above 1.1 mg/dL or doubled from baseline
- Persistent, severe headache that doesn’t respond to pain medication
- Visual changes such as blurred vision, seeing spots, sensitivity to light, or temporary vision loss
- Confusion or altered behavior
- Upper abdominal or chest pain that doesn’t go away with medication
- New shortness of breath or difficulty breathing while lying flat
Any one of these findings is sufficient. You don’t need to have all of them, and you don’t need proteinuria if other organ damage is confirmed through lab work.
A Newer Blood Test: The sFlt-1/PlGF Ratio
A blood test measuring two proteins produced by the placenta has emerged as a powerful tool for ruling preeclampsia in or out. The test calculates the ratio between a protein that damages blood vessels (sFlt-1) and one that protects them (PlGF). In preeclampsia, the damaging protein surges while the protective one drops.
A large study published in the New England Journal of Medicine found that a ratio of 38 or lower was extremely reliable at predicting that preeclampsia would not develop within the following week, with a negative predictive value of 99.3%. This makes the test particularly useful when symptoms are ambiguous: a low ratio can spare you from unnecessary hospitalization, while a high ratio prompts closer monitoring. This test is not yet standard everywhere but is increasingly available and used alongside traditional diagnostics.
Testing Doesn’t Stop at Delivery
Preeclampsia can develop after birth. Most postpartum cases appear within the first few days, but late postpartum preeclampsia can show up as far out as six weeks after delivery. The symptoms mirror those before delivery: high blood pressure, protein in the urine, headaches, visual changes, and upper abdominal pain.
If you develop any of these symptoms after giving birth, the same diagnostic workup applies: blood pressure readings, urine protein testing, and blood work checking liver enzymes, platelets, and kidney function. This is true even if your pregnancy was uncomplicated and you had no prior signs of preeclampsia.