If the patients' Activated Partial Thromboplastin Time (APTT) is prolonged, can we conclude that the patient is Lupus Anticoagulant (LA) positive? Is there any way to diagnose whether the patient is LA positive or not? Is it possible that the patients' APTT is prolonged but LA is negative?
Dear Asiful Islam,
a prolonged aPTT does not mean your patient is LA positive - it is just one of a couple of explanations! First of all, you want to exclude a factor activity deficiency (FVIII, FIX, X, XI, XII, prekallikrein, high-molecular-weight kininogen) or an inhibitor against one single factor (mainly, those are FVIII-inhibitors). Does the patient receive anticoagulant therapy, like heparin or any given DOAK?
LA diagnosis is not always easy and requires a combination of tests! Just look at this literature search in the link below!
http://www.ncbi.nlm.nih.gov/pubmed/?term=guidelines+lupus+anticoagulant+detection
Julian Strobel: Thanks very much for the clarification. If a patient is taking anticoagulant therapy; what would be the pattern of LA or APTT? Will there be any influence of the drug on LA or APTT?
Yes there might, depending on the anticoagulant! This question cannot answered that easily, as influences depend on the chemicals you use in your tests! Furthermore, in the new oral anticoagulants it depends on the time span between last dosis and drawing of the blood sample. Vitamin K antagonists will always influence your aPTT (remember, factors IX and X need Vitamin K to carboxylated in order to function properly and both have influence on your aPTT), if the patient is therapeutically anticoagulated (INR > 2).
So does heparine, but again this is dose-dependant and chemical-dependant (you can choose by your aPTT chemicals whether your aPTT is more sensible to heparine or to factor deficiency - you need to decide which!)!!!
As you see, this question is a tricky one!
For example: A patient of mine just recently was screened for Lupus anticoagulant, as she had suffered from a spontaneous lung emboly. She was anticoagulated with phenprocoumon (Vit.-K-antagonist) at the time, INR was 2.5! Her Lupus screen looked like this:
LA screen 86.0 sec (his is a diluted Russel´s viper venom time, norm
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