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In the June 2007 issue was a question
and answer related to livedo reticularis patients possibly having platelet
antiphospholipid antibodies that are treated with anticoagulants. The
question was whether the antiphospholipid antibody test can be negative
(within normal limits) in an LR patient who is taking Coumadin for chronic
atrial fibrillation. Here, Elizabeth M. Van Cott, MD, member of the CAP
Coagulation Resource Committee, and Rajni Mandal, MD, both of Massachusetts
General Hospital, Boston, provide additional information.
A. Livedo reticularis, or LR, is characterized
by a violaceous reticular or mottled pattern of the skin on the trunk,
arms, or legs due to increased visibility of the cutaneous venous plexus
by either venodilation or deoxygenation of the blood.1,2
LR can also be seen as a physiologic response to cold exposure
(cutis marmorata), or as a primary disorder due to spontaneous arteriolar
vasospasm. Secondary causes of LR commonly lead to increased resistance
to venous outflow, such as due to vasculitis, embolic phenomena, or a
hypercoagulable state. Medications such as amantadine have been associated
with LR. Livedo vasculitis, which is the formation of cutaneous nodules
and ulcerations secondary to ischemia and tissue infarction, can occur
with occlusion of vascular lumina.
Antiphospholipid antibody syndrome, or APS, is defined as thrombotic
or pregnancy complications that occur in temporal concordance with a persistently
positive test, or tests, for a lupus anticoagulant, anticardiolipin antibodies,
or anti-beta-2-glycoprotein-I antibodies. LR can be seen in APS and has
been associated with a poor outcome in patients with both APS and systemic
lupus erythematosus.2 In Sneddon syndrome,
which is characterized by ischemic cerebrovascular events with LR, patients
with livedo racemosa—in which the thickness of the reticular pattern
was greater than 10 mm—had a higher likelihood of having anticardiolipin
antibodies.3 Histological examination
of skin biopsies is not clinically indicated, since classic findings of
LR—vascular dilation without inflammation—can be nonspecific.
However, a biopsy can help exclude vasculitis, if suspected.
In a patient with LR and negative antiphospholipid antibodies, a clinical
evaluation, including the response to ambient temperature, can help distinguish
between primary or secondary LR. In addition, investigating autoimmune
connective tissue disease, infection such as hepatitis C, hypercoagulability,
or other causes for emboli is also recommended. Since the causes for secondary
LR are extensive and can be due to systemic disease, a full clinical evaluation
is warranted.
Warfarin does not affect the presence or absence of antiphospholipid
antibodies. In addition, warfarin is not expected to interfere with anticardiolipin
antibody or beta-2-glycoprotein-I antibody testing because these are enzyme-linked
immunosorbent assays. On the other hand, a number of coagulation experts
have anecdotally reported that warfarin can cause false-positive lupus
anticoagulant tests when using a dilute Russell viper venom time assay.
In our experience, the presence of warfarin can make interpreting dilute
partial thromboplastin time-based screening tests more difficult, possibly
leading to false-negative mixing study results. In theory, warfarin should
not interfere with the hexagonal phase lupus anticoagulant assay, but
as this has not been validated with certainty, it is recommended that
such results be interpreted cautiously. According to a consensus group,
specimens containing anticoagulants should not be tested for lupus anticoagulants,
but if such patients must be tested, the results must be interpreted with
caution.4
References
- Miyakis S, Lockshin MD, Atsumi T, et al.
International consensus statement on an update of the classification
criteria for definite antiphospholipid syndrome (APS). J
Thromb Haemost. 2006;4:295-306.
- Gibbs MB, English JC, Zirwas MJ. Livedo reticularis:
an update. J
Am Acad Dermatol. 2005;52:1009-1019.
- Francès C, Papo T, Wechsler B, et al. Sneddon
syndrome with or without antiphospholipid antibodies. A comparative
study in 46 patients. Medicine.
1999;78:209-219.
- Triplett DA. Antiphospholipid antibodies.
College of American Pathologists Consensus Conference XXXVI: Diagnostic
Issues in Thrombophilia. Arch
Pathol Lab Med. 2002;126:1424-1429.
Q. Is there a time frame after blood collection within which
a prothrombin time or activated partial thromboplastin time must be run
to ensure accurate results?
A. There is no consensus on the stability of prothrombin time or activated
partial thromboplastin time after collection in an appropriately filled
3.2 percent citrate tube. It is good practice to centrifuge the specimen
as soon as it arrives in the laboratory, leaving the plasma on top of
the cells.
The Clinical Laboratory Standards Institute (CLSI) document H21-A4 (2003)1
recommends that a PT test be completed within 24 hours from the time of
collection if stored at room temperature (between 18° and 24°C).
Other investigators have reported that the PT was stable for 24 hours
if the plasma was stored at room temperature2,3
or on ice (4°C).2 However, room-temperature
storage has also been recommended for a maximum of six hours4
and eight hours.5
Always follow the manufacturer's recommendations for your specific coagulation
analyzer/reagent combination, especially if these instructions are more
restrictive for the maximum storage time. For example, the Dade Behring
Innovin PT reagent package insert6 indicates
plasma should be tested within four hours after collection.
CLSI recommends that an APTT test be completed within four hours from
the time of collection if stored between 18° and 24°C.1
This time interval is suggested for patients on heparin therapy.2
Other investigators have recommended eight hours5
and 12 hours3 after the collection
time. However, the Dade Behring Actin FSL APTT reagent package insert
recommends testing be completed within two hours after blood collection.7
When PT and APTT testing cannot be completed within the recommended time
frame, the plasma should be removed from the cells and frozen at -20°C
for up to two weeks2 or three months8,
or at -70°C for up to six months1
or 18 months.8
References
- Clinical Laboratory Standards Institute.
Collection, Transport and Processing of Blood Specimens for Testing
Plasma-Based Coagulation Assays. Approved Guideline. 4th ed. Document
H21-A4. Wayne, Pa.:CLSI;2003.
- Adcock D, Kressin D, Marlar RA. The effect
of time and temperature variables on routine coagulation tests. Blood
Coagul Fibrinolysis. 1998;9:463-470.
- Rao LV, Okorodudu AO, Petersen JR, et al.
Stability of prothrombin time and activated partial thromboplastin time
tests under different storage conditions. Clin
Chim Acta. 2000;300:13-21.
- Van Geest-Daalderop JH, Mulder AB, Boonman-de
Winter LJ, et al. Preanalytical variables and off-site blood collection:
influences on the results of the prothrombin time/international normalized
ratio test and implications for monitoring of oral anticoagulant therapy.
Clin
Chem. 2005;51:561-568.
- Neofotistos D, Oropeza M, Ts'ao CH. Stability
of plasma for add-on PT and APTT tests. Am
J Clin Pathol. 1998;109:758-763.
- Dade Innovin [package insert]. Deerfield,
Ill.: Dade Behring Inc.; 2005.
- Dade Actin FSL activated PTT reagent [package
insert]. Deerfield, Ill.: Dade Behring Inc.; 2003.
- Woodhams B, Girardot O, Blanco MJ, et al.
Stability of coagulation proteins in frozen plasma. Blood
Coagul Fibrinolysis. 2001;12:229-236.
Peggy Fuller, MT (ASCP)
Supervisor
Hematology/Coagulation/Flow Cytometry
Memorial Regional Hospital
Hollywood, Fla.
Frederick L. Kiechle, MD, PhD
Medical Director, Clinical Pathology
Memorial Regional Hospital
Hollywood, Fla.
Member, CAP Special Chemistry Resource Committee
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