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.

What is the PFA-100 Closure Time Result Interpreter?

Enter PFA-100 Col/Epi and Col/ADP closure times to classify the platelet function pattern — normal, aspirin effect, or a significant primary haemostatic defect — against standard reference intervals. For haemostasis labs. It runs free in your browser on Gera Tools, with nothing uploaded.

PFA-100 Closure Time Result Interpreter

Name: PFA-100 Closure Time Result Interpreter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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 the PFA-100 works physically

The analyser draws citrated whole blood through a nitrocellulose membrane coated with collagen and either epinephrine (Col/Epi cartridge) or ADP (Col/ADP cartridge). The high-shear flow activates platelets, which adhere and aggregate on the collagen until they occlude the aperture. The instrument records the time from flow start to aperture occlusion — the closure time.

Because the test uses whole blood under physiological shear stress, it interrogates the entire primary haemostasis pathway: platelet adhesion via GPIb-vWF interaction, platelet activation, and platelet aggregation via GPIIb/IIIa. This is fundamentally different from platelet-poor plasma tests like PT or APTT, which test coagulation factors rather than platelet function.

Interpreting the combined pattern

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.

Why the two cartridges probe different things

Collagen/epinephrine pathway: Collagen activates platelets via GPVI and integrin α2β1. Epinephrine amplifies activation via α2-adrenergic receptors. Crucially, this secondary activation step is dependent on thromboxane A2 production through the COX-1 pathway — the same pathway that aspirin irreversibly inhibits. This makes the Col/Epi cartridge exquisitely sensitive to aspirin and most NSAIDs.

Collagen/ADP pathway: ADP activates platelets via P2Y1 and P2Y12 receptors — a route that bypasses COX-1 entirely. So ordinary aspirin dose does not prolong the Col/ADP closure time, but clopidogrel (which blocks P2Y12) does. The uncommon pattern of isolated Col/ADP prolongation with a normal Col/Epi result should prompt a medication review for ADP-receptor antagonists.

Commonly referenced reference intervals

Reference intervals vary between laboratories and with the citrate concentration of the collection tube. The commonly cited ranges are:

Col/Epi: 84–160 seconds
Col/ADP: 68–121 seconds

These figures are often cited in haematology references but your own laboratory’s validated local interval should always take precedence, particularly because the 3.2% citrate tube gives slightly different results from the 3.8% tube.

Factors that prolong closure time independently of platelet function

Several pre-analytical and patient variables affect closure times without indicating true platelet dysfunction:

Haematocrit below about 30%. Red cells contribute to the shear dynamics that drive platelet adhesion. Anaemia prolongs both cartridges. Always check the FBC before interpreting a prolonged result.
Platelet count below approximately 100 × 10⁹/L. Thrombocytopenia directly reduces aperture closure rate. A low platelet count must be corrected for or accounted for in interpretation.
Sample age and transport. The PFA-100 is time-sensitive — samples should be tested within 4 hours and ideally kept at room temperature. Cold temperatures partially activate platelets in vitro and can shorten or falsely normalise closure times.
Recent anti-platelet medication. Aspirin effect persists for 7–10 days (the lifespan of the affected platelets). Clopidogrel and other P2Y12 inhibitors have their own washout kinetics.

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.

This tool is designed for qualified haemostasis laboratory professionals as an interpretation aid. It does not replace clinical judgement or the laboratory’s own validated reference intervals. Results should always be interpreted in the context of the patient’s clinical history, current medications, and full blood count.