Short answer
PNH flow cytometry is the main lab method for diagnosing paroxysmal nocturnal hemoglobinuria, a rare acquired blood-cell disorder that can cause hemolysis, cytopenias, dark urine, bone marrow failure, and unusual blood clots. The test looks for blood cells missing GPI-linked proteins such as CD55 and CD59, often using FLAER-based testing on red cells and white cells.
Why PNH may be considered
| Clue | Why it matters | Related tests |
|---|---|---|
| Hemolysis | Red cells break down inside blood vessels. | LDH, haptoglobin, bilirubin, reticulocytes, urinalysis. |
| Unusual-site clots | PNH can increase thrombosis risk in uncommon locations. | Imaging, clotting workup, hematology review. |
| Bone marrow failure context | PNH can overlap with aplastic anemia or other marrow disorders. | CBC trend, marrow evaluation, clone-size monitoring. |
What flow cytometry measures
Flow cytometry checks for the absence or reduction of GPI-linked proteins on blood-cell surfaces. That is what makes PNH different from many other hemolysis or clotting problems. Some laboratories also report clone size in red cells, granulocytes, and monocytes, which helps interpret the clinical significance.
Because PNH can coexist with marrow failure, high-sensitivity methods and the right specimen matter. A negative blood result may not fully settle the question if the clinical suspicion is still high.
What the result means
The report may describe a PNH clone in multiple cell lines. Clone size, symptoms, hemolysis markers, clot history, kidney function, and marrow status all influence management. A tiny clone can mean something different from a large symptomatic clone, and a large clone can be more concerning when hemolysis or thrombosis is present.
Questions to ask
- Was testing ordered because of hemolysis, low counts, dark urine, or unusual clots?
- Which cell lines were tested, and what was the clone size?
- Are LDH, haptoglobin, bilirubin, reticulocytes, and kidney markers being followed?
- Does the result need repeat monitoring or treatment discussion with hematology?
Related guides: LDH, haptoglobin, and hemolysis labs, reticulocyte count, urinalysis, and JAK2 testing.
What the result still cannot prove
PNH flow cytometry can detect a clone, but it does not by itself explain every cause of hemolysis, thrombosis, or marrow failure, so the rest of the workup still matters.
FAQ
Is PNH inherited?
Usually no. Most PNH is acquired, not inherited, and arises from a somatic variant in a blood-forming stem cell.
Why is flow cytometry the key test?
Because it can detect missing GPI-linked proteins such as CD55 and CD59 on red cells, white cells, and sometimes granulocytes with FLAER-based methods.
Can a blood test miss PNH?
A negative or low-level blood result does not always end the question if suspicion is high; specimen type and assay sensitivity matter.
What does clone size mean?
Clone size describes how many blood cells show the PNH pattern, and it helps clinicians judge how much the result may matter clinically.
Which other labs are usually checked?
CBC, LDH, bilirubin, haptoglobin, reticulocyte count, urinalysis, and kidney markers are commonly reviewed alongside the flow result.
Does PNH always mean dark urine?
No. Dark urine can happen, especially in hemolysis, but some people present with fatigue, cytopenias, or thrombosis instead.
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