Reader Responses: How would you treat a patient with a prolonged PTT and antiphospholipid antibodies?

Here’s how readers responded to a You Make the Call question about a patient with a prolonged PTT and antiphospholipid antibodies.

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It seems that the patient doesn’t have bleeding or thrombotic issues, therefore I would continue to taper the steroid. I agree that FIX activity less than 1 is due to interference of the inhibitor.

Matteo Dragani, MD
Turin, Italy

I would get the patient off steroids and not treat unless she has any symptoms of bleeding.

Hassan Sheikh, MD
Lance and Ellen Shaner Cancer Pavilion
State College, PA

Taper steroids and observe.

David Ross
Voorhees, NJ

The activated PTT (aPTT) is clearly prolonged, prothrombin time mildly prolonged, and thrombin time normal. There is no heparin in the plasma, lupus anticoagulant (LA; diagnosed earlier) should certainly be confirmed (screening and confirmation). The FIX:C activity (<1%) could be a laboratory artifact caused by high-titer LA; also the FIX inhibitor is falsely positive due to the LA. I would have expected FVIII:C activity to be lower as well (if measured by a modified aPTT-based assay, but not if measured by a chromogenic FVIII:C assay). Evidently, the patient does not need prednisone. She needs observation but no treatment.

Bernhard Lämmle, MD
Johannes Gutenberg University Mainz
Mainz, Germany

This patient appears to have acquired hemophilia B, as evidenced by an inhibitor and reduced Bethesda units for FIX. It would be interesting to see a repeat PTT and FIX activity level after exposure to prednisone. Despite the patient not having a history of bleeding at age 78, we do not know how long the PTT has been elevated. This is an acquired coagulopathy and perhaps this patient has not had the inhibitor long enough to have experienced a bleeding event.

Brian J. Leberthon, MD
West Covina, CA

LA plus FIX inhibitor is uncommon and is more frequently seen with FVIII, but I think it could be seen with FIX too. We suggest doing a test that differentiates a specific factor inhibitor from one that is non- specific, such as LA. This could be an immunologic assay.

Maria V. Garcia Pallas, MD
Caguas, Puerto Rico

Since the positivity of antiphospholipid antibodies is a laboratory finding, I would probably not treat her except if she had a thromboembolic event. Then she should be treated with a vitamin K antagonist.

Stamatis Karakatsanis, MD
University of Athens
Athens, Greece

The patient may have either hemophilia B or a prolonged PTT due to the FIX inhibitor. It might be helpful to perform a mixing study and to repeat the PTT with an LA-insensitive assay. In either case, with a lifetime history of no bleeding tendencies, she does not have a clinical problem. Hemophilia B can produce surprisingly little bleeding diathesis even with this low of an FIX level.

Taper her off prednisone rapidly, figure out whether she’s a de novo hemophiliac B, and reassure her.

Howard L. Ritter Jr., MD
Toledo, OH

In my opinion, more tests are necessary before making a decision. This includes performing a “mixing test” with normal plasma, testing for anti-β2 -glycoprotein I antibodies, determining the class of immunoglobin and the titer of antiphospholipid antibodies, a search for antinuclear and anti-dsDNA (to confirm systemic lupus erythematosus ), and serial determinations every three months. For the moment, because the patient has been asymptomatic for many years, observation would be wise. Prolonged corticotherapy in such doses and at this age could be dangerous. I would use caution in performing invasive procedures, or with trauma.

Radu Gologan, MD, PhD
Bucharest, Romania

In this scenario, without antiphospholipid syndrome and without a history of thrombosis, she doesn’t need to be treated. She has lived several years without thrombosis with these conditions. You said that you believe that these findings are because antiphospholipid antibodies “are likely also interfering with the FIX inhibitor test.” I disagree. You tell us that she had FVIII activity of 63. To assert that the result of FIX activity is due to antibodies interfering, you must have the same result with FVIII, FIX, FXI, FXII, and FX (if you decided to use aPTT instead of prothrombin time only in a FX assay). Remember that some manufacturers formulate low phospholipid aPTT reagents to enhance detection of LA – for example, Siemens Actin FSL, Beckman-Coulter HemosIL aPTT-SP, and Stago PTT-LA.

I usually use two different reagents: one with low-phospholipid reagents to detect LA and another to avoid interference with low interference activity such as Siemens Actin FS and Stago’s C.K. Prest. Both are considered to exhibit relatively low responsiveness to LA. You must determine FIX, FVIII, FXI, FXII and FX levels with any reagent that shows low activity to LA (Siemens’ Actin FS or Stago’s C.K. Prest).

I used to perform the inhibitor detection assay at 15, 30, and 60 minutes, incubating the samples at 98.6˚F, ice melting temperature, and room temperature, obviously with a pool of blood plasma as a control. Sometimes the antibodies have wide thermic amplitude, other times they are cold or warm (as in hemolytic anemia). I agree with your advice to treat her with corticosteroids as soon as possible because we cannot discount an acquired inhibitor.

You must perform studies to disclose a hidden cancer, which may be responsible for an  acquired inhibitor factor, usually FVIII. Furthermore, it is possible that your patient has developed an acquired inhibitor associated with an antiphospholipid antibody. Remember that acquired hemophilia A has an annual incidence of 1.5/million and mostly affects people between the ages of 75 and 80, whereas thrombosis associated with LA occurs at a much younger age. First you can try corticosteroids (prednisone).  If the patient is refractory, then you could try rituximab, cyclophosphamide, azathioprine, vincristine, cyclosporine, and high-dose immunoglobin. If she has a bleeding episode, start with high doses of FIX.

Sergio Barragan, MD, PhD
Buenos Aires, Argentina 

I would look for a malignancy, too. Depending on the level of the antibodies, I would start her on aspirin.

Sarina Levy-Mendelovich, MD
New York, NY

I would do the following:

  1. Review history. A true specific FIX inhibitor is likely to present with bleeding. If there is no evidence of bleeding tendency, it is more likely an LA clinically.
  2. Distinguish specific from nonspecific inhibitor:
  • Nonspecific factor is neutralized with phospholipid during the confirmatory step. This will not occur with a specific inhibitor.
  • Repeated testing will show erratic values of many factors (and their inhibitors). I would choose one from the extrinsic and one from the common pathway. On the other hand, repeat testing would point toward one factor only in the case of a specific inhibitor.
  • PTT mixing studies usually show delayed prolongation with 37˚C incubation in the case of a LA.

Prem Sobti, MD
Cape Girardeau, MO

Stop prednisone.

Frank Bontempo, MD
Pittsburgh, PA

I would “treat” the patient to confirmatory laboratory testing after possibly calling the director of the lab that put out some of those initial lab results.  The data are curious.  Was the FVIII assay parallel to the standard curve or nonparallel?  I would start re-evaluating the patient in my own hospital lab, including repeating prothrombin time (PT) and PTT with 1:1 mix on PT and PTT, repeat the lupus inhibitor assay, FVIII, and FIX assays.  In a patient with no bleeding from early adulthood through age 78, I would not conclude that she truly has severe FIX deficiency.  Acquired disorders with autoantibodies to FIX are rare.  Similarly, inherited FIX deficiency with inhibitor formation in a phenotypic female would also be very rare.  If the abnormality is indeed related to a strong lupus inhibitor (making PT slightly prolonged and PTT even more prolonged), why is the FVIII assay not affected?  There may be people with antiphospholipid syndrome who have an antibody that clears FIX similar to the acquired hypoprothrombinemia associated with lupus inhibitor in children, but  I have not heard of that situation. Furthermore,  in the   hypoprothrombinemia, I thought it was due to clearing rather than an inhibitory antibody.  If the patient truly had severe FIX deficiency with LA and bleeding (or needed surgery), I might then consider immunosuppression.

Kenneth D. Friedman, MD
Blood Center of Wisconsin
Milwaukee, WI

I would rapidly taper steroids over 7 to 10 days, then repeat the LA panel. Repeat inhibitor studies with serial dilutions of plasma, which should dilute out the effect of a nonspecific inhibitor such as a lupus-type anticoagulant.

James Granfortuna, MD
Greensboro, NC

 I suspect that the low FIX activity measured is factitious, as is the positive FIX Bethesda titer, and that both are likely due to LA interference in the assays.  Acquired FIX inhibitors in a non-hemophiliac patient would be quite unusual and I have in fact never seen one.  Furthermore, if this were a real FIX inhibitor, I would expect that the patient would have some bleeding manifestations.

LAs can, in some patients, cause intrinsic factor activities (factors VIII, IX, XI and XII) to appear low due to an assay interference.  Just as in this patient, only one factor may demonstrate interference, or multiple intrinsic factors can show assay interference. The patterns can be quite variable.  As lupus anticoagulants are inhibitors, they can also cause factor inhibitor assays to be falsely positive, usually leading to a titer of <5 BU.

To confirm assay interference, the FIX activity should be determined using a method that is either not LA-sensitive or not as LA-sensitive.  FIX chromogenic assays do not demonstrate LA interference as they are less phospholipid-dependent and they are performed at a high dilution.  These assays are only available on a researchuse-only basis and are performed in very few laboratories in the U.S. So, while this would be the ideal solution, it may not be an option.  Another possibility is to make certain that the original assay was performed using at least three dilutions, and it should be determined whether there were any nonparallelism, as this would indicate a nonspecific inhibitor such as an LA.  A true FIX inhibitor would not show nonparallelism in a FIX activity assay.  Not all LAs can be diluted in factor activity assays, and in my experience, this is PTT re-agent as well as the specific LA-dependent.  If there were no nonparallelism present in the FIX assay, I would evaluate the results of the Bethesda assay (see paragraph below) and pending that, may recommend sending the sample to a laboratory that uses a different and ideally less LA-responsive PTT re-agent.  Some PTT reagents, such as Siemens FSL, are manufactured to be lupus-sensitive.  FSL in fact, stands for factor sensitive, LA-sensitive. If the FIX activity assay were significantly higher or even normal using a non-LA–sensitive re-agent, this would suggest assay interference and the prednisone could be discontinued.  A FIX antigen could be performed and would be expected to be normal if the activity were factitiously low due to assay interference, but a normal FIX antigen would not rule out a FIX inhibitor.

The manner in which the Bethesda assay is performed can also help detect the presence of a nonspecific inhibitor. The Bethesda assay is often performed using multiple dilutions of patient plasma in buffer so that an inhibitor titer (Bethesda titer [BT]) can be determined.  Patient plasma is typically tested neat, at 1:2 and 1:5 dilutions, although additional dilutions may be required with high titer inhibitors.  These initial patient dilutions are referred to as “dependent dilutions.”  When the factor activity is performed on these “dependent dilutions” following incubation, the analyzer should be programmed to perform the activity assay at 1:10 and 1:20 dilutions. The 1:10 and 1:20 dilution results should be evaluated for nonparallelism. This step will aid in the detection of nonspecific inhibitor effect, which could potentially result in a false-positive BT.  Some nonspecific inhibitors that cannot be distinguished in a factor activity assay may be detected in the dilutions of the Bethesda assay.  This enhanced sensitivity to nonspecific inhibitors may be due to the fact that this step of the Bethesda assay has added pooled normal plasma and is subject to incubation. As an example, when a strong LA sample without a FIX inhibitor is tested in a FIX activity assay, it may result in no measurable FIX activity at all dilutions tested. In the FIX Bethesda assay, the 1:10 and 1:20 dilutions of this strong LA sample often show nonparallelism with increasing activity comparing the 1:10 to the 1:20 dilution.

Testing in the coagulation laboratory can be complex and results difficult to interpret correctly.  This is often due to the presence of assay interferences such as circulating inhibitors, including LAs or anticoagulant drugs that function as inhibitors (e.g., direct oral anticoagulant agents). The low FIX activity and positive FIX Bethesda assay in this patient could represent LA interference. Confirming such interference can be difficult but is important so that unneeded prednisone therapy can be discontinued.


Adcock DM, Favaloro EJ. Pearls and pitfalls in factor inhibitor assays. Int J Lab Hematol. 2015;37(Suppl 1):52-60.

Dorothy M. Adcock, MD
CMO Laboratory Corporation of America
Burlington, NC

It is not clear to me why the patient was treated with prednisone. This is a patient with a lab abnormality and no clinical disease. I would taper prednisone and stop it. I would do no more lab tests unless the patient had an actual clinical problem with bleeding or clotting.

Phillip O. Periman, MD
Amarillo, TX

She has no symptoms, so I would discontinue prednisone. I would measure the factor by a chromogenic assay.

Joseph Holahan, MD
San Antonio, TX

I do not believe the patient has severe hemophilia B suddenly at age 78 with no history of bleeding problems. She is not acting like an acquired hemophiliac.  Has she has had any surgeries in the past?  Was the reason she was on prednisone because of the antibody? Are you able to get a mixing study?  That should be able to clarify between factor deficiency and the presence of an antibody.

Nadia Ali, MD
Temple University Hospital
Philadelphia, PA