Flow cytometry — used to analyze blood cells one by one — is considered the main test for diagnosing paroxysmal nocturnal hemoglobinuria (PNH). However, several other blood tests can help doctors get a clearer picture of what’s causing your symptoms, whether PNH may be the cause, and whether you’re developing serious complications.

Here are some of the most common blood tests recommended when doctors suspect someone may have PNH and what their results show. These tests may also be used to monitor your condition during follow-ups if you’ve already been diagnosed with this rare disease.

1. Lactate Dehydrogenase

Lactate dehydrogenase (LDH) is a protein found in red blood cells (RBCs). High levels of LDH in your blood may indicate hemolysis — abnormal destruction of RBCs — is taking place in your body. In PNH, RBCs are attacked and prematurely destroyed by the complement system, one part of the immune system. If your LDH levels are high and it’s unclear why, hematology specialists may suspect PNH.

According to Cleveland Clinic, normal LDH levels ranges are as follows:

• 135 to 225 units per liter in adults assigned male at birth
• 135 to 214 units per liter in adults assigned female at birth

These ranges are higher among children.

In people with the most common type of PNH, LDH levels are typically more than 1.5 times the highest normal range.

After PNH is diagnosed, blood tests to check LDH may be performed periodically to assess:

• Whether you’re developing blood clots
• Whether you have bone marrow failure
• Whether PNH medications are effective
• Whether PNH gets worse if you stop taking medication

2. Liver Function Tests

Bilirubin is a yellow pigment produced by the destruction of RBCs. The liver is responsible for breaking down bilirubin, so levels of the substance can provide information about how well the liver is working and how rapidly red blood cells are being destroyed.

Bilirubin can be measured in different ways. Normal ranges of bilirubin are:

• Less than 0.3 milligrams per deciliter when direct or conjugated bilirubin is measured
• 0.1 to 1.2 milligrams per deciliter when total bilirubin is measured

Higher levels of bilirubin may indicate that too many RBCs are being destroyed, making PNH a more likely cause.

3. Complete Blood Count

A complete blood count (CBC) assesses the number of different types of blood cells in a blood sample. It’s used to check for anemia (low levels of RBCs). It can also check for low levels of platelets, blood cell fragments that play an important role in blood clotting.

Read more about symptoms of hemolytic anemia with PNH.

Sometimes a CBC includes a differential, which means that white blood cells (WBCs, which function as part of the immune system) and immature blood cells will also be counted.

Other than anemia, CBC of people with PNH may show pancytopenia, in which levels of all types of cells — red blood cells, white blood cells, and platelets — are reduced. This is because PNH is associated with bone marrow failure, a condition in which your bone marrow cannot produce enough cells.

4. Reticulocyte Count

Reticulocytes are immature RBCs. Measuring reticulocytes helps doctors understand whether your body is producing enough RBCs. In healthy adults, the normal range for reticulocytes is between 0.5 and 2.5 percent of the RBCs in blood.

In people with PNH, reticulocytes may be high because your body is trying to rapidly replace RBCs destroyed by hemolysis. Reticulocytes may also be low in people with PNH if they have a preexisting deficiency of iron,vitamin B12, or folate or if their PNH is complicated by bone marrow failure. If your results show low reticulocytes, your doctor may recommend nutritional supplements to help boost RBC production.

They may also consider ordering a bone marrow biopsy to check for bone marrow disorders like aplastic anemia or myelodysplastic syndrome. Everyone who has PNH has problems with their bone marrow to some degree. Many also have one of these disorders at the same time.

5. Serum Haptoglobin and Free Hemoglobin

Haptoglobin is a protein that clears away unattached hemoglobin and substances left behind when RBCs are damaged. In people with PNH, hemolysis destroys so many RBCs that haptoglobin is used up and hemoglobin isn’t cleared away.

The normal range for haptoglobin in healthy individuals is between 41 and 165 milligrams per deciliter. In a healthy person who doesn’t have hemolytic anemia, hemoglobin levels are considered normal up to 5 milligrams per deciliter. Low haptoglobin and higher-than-normal free hemoglobin in your blood can signal the presence of PNH.

6. Iron Testing

Your body needs adequate levels of iron to produce enough hemoglobin to carry oxygen to your cells and tissues. There are many ways to measure iron levels, including these:

• Serum iron is iron currently carried in the blood. Normal range is 60 to 170 micrograms per deciliter.
• Transferrin is a protein responsible for moving iron through the body. Normal saturation range is 20 percent to 50 percent.
• Ferritin is iron in a form the body uses for storage. Normal ranges are 12 to 150 nanograms per milliliter in females and 12 to 300 nanograms per milliliter in males, according to Mount Sinai.

Lower-than-normal values may point to PNH as a potential cause.

Talk With Others Who Understand

On myPNHteam, the social network for people with paroxysmal nocturnal hemoglobinuria and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with PNH.

Have you had laboratory tests for PNH? Did your doctor discuss your results and what they mean? Share your experience in the comments below, or start a conversation by posting on your Activities page.