What are the normal PFA-100 reference ranges?

Commonly cited intervals are 84 to 160 seconds for the Col/Epi cartridge and 68 to 121 seconds for the Col/ADP cartridge. Ranges depend on the citrate tube and local validation, so confirm against your own laboratory limits.

What does a prolonged Col/Epi with a normal Col/ADP mean?

This is the classic signature of aspirin or other COX-inhibiting NSAID effect. The epinephrine pathway is more sensitive to cyclo-oxygenase inhibition, so it prolongs first while the ADP cartridge stays normal.

When are both cartridges prolonged?

Prolongation of both Col/Epi and Col/ADP suggests a significant primary haemostatic defect such as von Willebrand disease, intrinsic platelet dysfunction, thrombocytopenia, or severe anaemia. It warrants von Willebrand testing and platelet aggregometry.

Does a normal PFA-100 rule out a bleeding disorder?

No. The PFA-100 is a screening test with limited sensitivity for mild platelet defects and type 1 von Willebrand disease. A normal result does not exclude a clinically relevant bleeding tendency in a patient with a suggestive history.

Why is the test affected by haematocrit and platelet count?

The assay relies on platelets adhering and aggregating under flow within a membrane aperture. A low haematocrit (below about 30%) or low platelet count (below about 100) reduces this process and prolongs closure times independent of true platelet function.

PFA-100 Closure Time Result Interpreter

The PFA-100 measures how quickly whole blood, drawn through a small aperture under high shear, forms a platelet plug. Two cartridges probe different activation pathways, and the combined pattern points toward the cause of any prolongation.

How it works

Each cartridge has its own reference interval, and the pattern of which is prolonged drives interpretation:

Col/Epi normal,    Col/ADP normal     normal primary haemostasis
Col/Epi prolonged, Col/ADP normal     aspirin / NSAID effect
Col/Epi prolonged, Col/ADP prolonged  vWD, platelet defect, low platelets/Hct
Col/Epi normal,    Col/ADP prolonged  uncommon — recheck, consider clopidogrel

The epinephrine cartridge is the more sensitive to cyclo-oxygenase inhibition, which is why aspirin prolongs it first while the ADP cartridge stays within range.

Notes and limitations

Closure times rise with low haematocrit and low platelet count regardless of true platelet function, so always interpret alongside the full blood count. The PFA-100 is a screen, not a confirmatory test: a normal result cannot exclude a mild platelet defect or type 1 von Willebrand disease, and abnormal results should be followed up with von Willebrand factor assays and light-transmission aggregometry.