Investigations
1st investigations to order
urine dipstick
Test
Almost all patients with classic PNH have episodes of haemoglobinuria during haemolytic episodes.
Result
haemoglobinuria
urine microscopy
Test
Stainable iron in the urine is evidence of intravascular haemolysis.
Result
haemosiderinuria
FBC
Test
Unilineage or multilineage cytopoenias may co-exist (e.g., leukopenia, thrombocytopoenia). Evidence of dysplastic changes in bone marrow and/or peripheral blood may suggest underlying myelodysplasia.
Result
anaemia or cytopoenia (e.g., granulocytopoenia, thrombocytopoenia)
reticulocyte count
Test
Assessed to confirm intravascular haemolysis.
Result
increase indicates haemolysis
serum LDH
Test
Other sources of tissue destruction may give the same result; may be resolved by isozyme testing.
Liver damage is characterised by elevated alanine aminotransferase, whereas intravascular haemolysis is not.
Sample must be processed at once to avoid in vitro haemolysis.
Result
increase indicates intravascular haemolysis
unconjugated bilirubin
Test
Assessed to confirm intravascular haemolysis.
Result
elevated
D-dimer
Test
Assesses the risk of thrombosis; elevated D-dimer level suggests an increased risk.
Result
may be elevated
Investigations to consider
haptoglobin
Test
Assessed to confirm intravascular haemolysis.
Result
low
flow cytometry for glycosylphosphatidylinositol anchor or anchored proteins
Test
Testing should be done with at least two reagents on RBCs, granulocytes and monocytes.[2]
Result
>1% to 3% of anchor-deficient granulocytes indicates a diagnosis of PNH
fluorescent aerolysin
Test
Done on granulocytes and monocytes. Most sensitive and accurate test.[22]
Result
detects glycosylphosphatidylinositol anchor; >1% to 3% deficient cells indicate PNH
immunotyping
Test
Detects missing proteins on PNH cells.
Result
variable
antiglobulin (Coombs) test
Test
Usually negative except after treatment with complement C5 inhibitors.
Result
detects IgG and C3 on the RBC surface, excludes autoimmune haemolytic anaemias
serum iron, serum ferritin
Test
Patients with PNH have unusually large iron losses and may be iron deficient.
Result
low
serum creatinine and urea
Test
Both acute and chronic renal insufficiency may occur.[10]
Result
variable
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