Approach Considerations
Laboratory studies for suspected hemophilia include a complete blood cell count, coagulation studies, and a factor VIII (FVIII) assay. Never delay indicated coagulation correction pending diagnostic testing.
On the hemoglobin/hematocrit assay, expect normal or low values. Expect a normal platelet count. On coagulation studies, the prothrombin time (which assesses the extrinsic coagulation pathway) and thrombin time are normal.
Usually, the activated partial thromboplastin time (aPTT) is prolonged; however, a normal aPTT does not exclude mild or even moderate hemophilia because of the relative insensitivity of the test. The aPTT is significantly prolonged in severe hemophilia.
For FVIII assays, levels are compared with a normal pooled-plasma standard, which is designated as having 100% activity or the equivalent of FVIII U/mL. Normal values are 50-150%. Values in hemophilia are as follows:
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Mild: > 5%
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Moderate: 1-5%
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Severe: < 1%
Aging, pregnancy, oral contraceptive use, and estrogen replacement therapy are associated with increased FVIII levels. Because FVIII is a large molecule that does not cross the placenta, the diagnosis can be made at birth with quantitative assay of cord blood.
Three main FVII assay methods are in use: one-stage and two-stage clotting assays and a two-stage chromogenic method. In approximately one-third of patients with mild hemophilia, FVIII levels on the automated one-stage FVIII assay are significantly higher than—typically, more than double—those of the two-stage coagulation assay. [25, 26]
Those discrepancies, which result from differences in the underlying FVIII mutations in these patients, can result in missed diagnoses or mismanagement due to underestimation of bleeding risk. [25, 27] Given the possibility of discrepant hemophilia A, as this condition is termed, use of the chromogenic FVIII assay combined with FVIII gene mutation analysis has been recommended for diagnosis of mild hemophilia A. [25]
Differentiation of hemophilia A from von Willebrand disease is possible by observing normal or elevated levels of von Willebrand factor antigen and ristocetin cofactor activity. A caveat to this is the rare patient with type 2N von Willebrand disease in which the VW antigen and activity levels are normal but binding to FVIII is impaired resulting in short circulating half-life of Factor VIII and low levels. While type 2N VWD is very rare, it is relevant to exclude this diagnosis as those patients may require therapy wtih combined VWF/FVIII product rather than isolated FVIII concentrate. Bleeding time is prolonged in patients with von Willebrand disease but conflicting reports of presence of elevation patients with hemophilia as well of lack of standardization and familiarity with proper performance of this assay limits the utility of the bleeding time as a diagnostic strategy.
In patients with an established diagnosis of hemophilia, periodic laboratory evaluations include screening for the presence of FVIII inhibitor and screening for transfusion-related or transmissible diseases such as hepatitis and HIV infection. Screening for infection may be less important in patients who receive only recombinant FVIII concentrate.
Imaging studies for acute bleeds
Early and aggressive imaging is indicated, even with low suspicion for hemorrhage, after coagulation therapy is initiated. Imaging choices are guided by clinical suspicion and the anatomic location of involvement.
Head CT scans without contrast are used to assess for spontaneous or traumatic intracranial hemorrhage. Perform magnetic resonance imaging (MRI) on the head and spinal column for further assessment of spontaneous or traumatic hemorrhage. MRI is also useful in the evaluation of the cartilage, synovium, and joint space.
Ultrasonography is useful in the evaluation of joints affected by acute or chronic effusions. This technique is not helpful for evaluating the bone or cartilage. Special studies such as angiography and nucleotide bleeding scan may be clinically indicated.
Testing for Inhibitors
Laboratory confirmation of a FVIII inhibitor is clinically important when a bleeding episode is not controlled despite infusion of adequate amounts of factor concentrate. For the assay, the aPTT measurement is repeated after incubating the patient's plasma with normal plasma at 37°C for 1-2 hours. If the prolonged aPTT is not corrected, the inhibitor concentration is titrated using the Bethesda method. Ideally, the Nijmegen modification of the Bethesda inhibitor assay should be used to detect an inhibitor if the mixing test result is positive. [13]
By convention, more than 0.6 Bethesda units (BU) is considered a positive result for an inhibitor. Less than 5 BU is considered a low titer of inhibitor, and more than that is a high titer. The distinction is clinically significant, as patients with low-titer inhibitors may respond to higher doses of FVIII concentrate while those with high-titer inhibitors require treatment with agents that bypass FVIII and consideration for induction of immune tolerance.
Caution is warranted when obtaining blood samples for coagulation assays from heparinized central lines because of the effect of heparin contamination on all coagulation test results. The excess heparin causes false-positive results and/or higher inhibitor titer values than are actually present in the patient, because heparin is also an inhibitor of coagulation.
One study found significant heparin contamination in 45% of all specimens obtained through implanted venous access devices. These researchers suggested that all blood samples obtained from such devices, which are usually flushed with heparin, should be treated with heparinase before performing an inhibitor assay. [28]
Carrier Testing and Fetal Testing
Screening for carrier status can be performed by measuring the ratio of FVIII coagulant activity to the concentration of von Willebrand factor (vWF) antigen. A ratio that is less than 0.7 suggests carrier status.
Direct genetic testing for known gene mutation is more accurate. Linkage analysis by restriction fragment length polymorphism (RFLP) in multiple family members can be used. Direct mutation analysis is available in several laboratories for unknown FVIII mutations. Inversion of the FVIII gene can be detected by Southern blot.
For prenatal testing, carriers whose mutation has been identified can have chorionic villus sampling at approximately 10-12 weeks' gestation or amniocentesis at 16-20 weeks' gestation to obtain fetal cells for DNA analysis or for linkage studies. If DNA analysis cannot be performed, then fetal blood obtained by fetoscopy at approximately 20 weeks' gestation can be assayed for factor VIII level.
All of those procedures carry a risk ranging from a low of 0.5% for maternal-fetal complications to a high of 1-6% for fetal death from fetoscopy. These procedures should be undertaken only after patients receive intense genetic and obstetric counseling. Genetic counseling before the woman becomes pregnant is ideal and may help couples make informed decisions before conception.
Noninvasive prenatal diagnosis using quantitative digital polymerase chain reaction testing of free fetal DNA in the maternal circulation has been reported. However, this technique remains a research tool. [29]
If the fetus is a female, the couple may elect to carry the pregnancy to term because carriers rarely have bleeding problems. If the fetus is a severely affected male, the couple must make a decision about continuing the pregnancy to term. With pregnancies that will be carried to term, prenatal diagnosis allows for planning of delivery so as to minimize the risk of intracranial hemorrhage (eg, avoidance of vacuum devices). [29]
Radiography
Radiography for joint assessment is of limited value in acute hemarthrosis. Evidence of chronic degenerative joint disease may be visible on radiographs in patients who have been untreated or inadequately treated or in those with recurrent joint hemorrhages. In these patients, radiographs may show synovial hypertrophy, hemosiderin deposition, fibrosis, and damage to cartilage that progresses with subchondral bone cyst formation.
Hemophilic arthropathy evolves through 5 stages, starting as an intra-articular and periarticular edema due to acute hemorrhage and progressing to advanced erosion of the cartilage with loss of the joint space, joint fusion, and fibrosis of the joint capsules. [8] See the image below. For discussion of the 5-stage Arnold-Hilgartner classification of hemophilic arthropathy, see Imaging in Musculoskeletal Complications of Hemophilia.
Photograph of a hemophilic knee at surgery, with synovial proliferation caused by repeated bleeding; synovectomy was required.
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Coagulation pathway.
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The hemostatic pathway. APC = activated protein C (APC); AT-III = antithrombin III; FDP = fibrin degradation products; HC-II = heparin cofactor II; HMWK = high-molecular-weight kininogen; PAI = plasminogen activator inhibitor; sc-uPA = single-chain urokinase plasminogen activator; tc-uPA = two-chain urokinase plasminogen activator; TFPI = tissue factor pathway inhibitor; tPA = tissue plasminogen activator
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Structural domains of human factor VIII. Adapted from: Stoilova-McPhie S, Villoutreix BO, Mertens K, Kemball-Cook G, Holzenburg A. 3-Dimensional structure of membrane-bound coagulation factor VIII: modeling of the factor VIII heterodimer within a 3-dimensional density map derived by electron crystallography. Blood. Feb 15 2002;99(4):1215-23; Roberts HR, Hoffman M. Hemophilia A and B. In: Beutler E, Lichtman MA, Coller BS, et al, eds. Williams Hematology. 6th ed. NY: McGraw-Hill; 2001:1639-57; and Roberts HR. Thoughts on the mechanism of action of FVIIa. Presented at: Second Symposium on New Aspects of Haemophilia Treatment; 1991; Copenhagen, Denmark.
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Possible genetic outcomes in individuals carrying the hemophilic gene.
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Photograph of a teenage boy with bleeding into his right thigh as well as both knees and ankles.
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Photograph of the right knee in an older man with a chronically fused, extended knee following open drainage of knee bleeding that occurred many years previously.
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Photograph depicting severe bilateral hemophilic arthropathy and muscle wasting. The 3 punctures made into the left knee joint were performed in an attempt to aspirate recent aggravated bleeding.
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Radiograph depicting advanced hemophilic arthropathy of the knee joint. These images show chronic severe arthritis, fusion, loss of cartilage, and joint space deformities.
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Radiograph depicting advanced hemophilic arthropathy of the elbow. This image shows chronic severe arthritis, fusion, loss of cartilage, and joint space deformities.
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Photograph of a hemophilic knee at surgery, with synovial proliferation caused by repeated bleeding; synovectomy was required.
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Large amount of vascular synovium removed at surgery.
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Microscopic appearance of synovial proliferation and high vascularity. If stained with iron, diffuse deposits would be demonstrated; iron-laden macrophages are present.
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Large pseudocyst involving the left proximal femur.
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Transected pseudocyst (following disarticulation of the left lower extremity due to vascular compromise, nerve damage, loss of bone, and nonfunctional limb). This photo shows black-brown old blood, residual muscle, and bone.
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Dissection of a pseudocyst.
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Transected pseudocyst with chocolate brown-black old blood.
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Photograph of a patient who presented with a slowly expanding abdominal and flank mass, as well as increasing pain, inability to eat, weight loss, and weakness of his lower extremity.
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Plain radiograph of the pelvis showing a large lytic area.
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Intravenous pyelogram showing extreme displacement of the left kidney and ureter by a pseudocyst.
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Photograph depicting extensive spontaneous abdominal wall hematoma and thigh hemorrhage in an older, previously unaffected man with an acquired factor VIII inhibitor.
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Magnetic resonance image of an extensive spontaneous abdominal wall hematoma and thigh hemorrhage in an older, previously unaffected man with an acquired factor VIII inhibitor.
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Coagulation Cascade
Tables
Classification |
Factor Activity, % |
Cause of Hemorrhage |
Mild |
>5-40 |
Major trauma or surgery |
Moderate |
1-5 |
Mild-to-moderate trauma |
Severe |
< 1 |
Spontaneous |
Indication or Site of Bleeding |
Factor level Desired, % |
FVIII Dose, IU/kg |
Comment |
Severe epistaxis; mouth, lip, tongue, or dental work |
20-50 |
10-25 |
Consider aminocaproic acid (Amicar), 1-2 d |
Joint (hip or groin) |
40 |
20 |
Repeat transfusion in 24-48 h |
Soft tissue or muscle |
20-40 |
10-20 |
No therapy if site small and not enlarging (transfuse if enlarging) |
Muscle (calf and forearm) |
30-40 |
15-20 |
None |
Muscle deep (thigh, hip, iliopsoas) |
40-60 |
20-30 |
Transfuse, repeat at 24 h, then as needed |
Neck or throat |
50-80 |
25-40 |
None |
Hematuria |
40 |
20 |
Transfuse to 40% then rest and hydration |
Laceration |
40 |
20 |
Transfuse until wound healed |
GI or retroperitoneal bleeding |
60-80 |
30-40 |
None |
Head trauma (no evidence of CNS bleeding) |
50 |
25 |
None |
Head trauma (probable or definite CNS bleeding, eg, headache, vomiting, neurologic signs) |
100 |
50 |
Maintain peak and trough factor levels at 100% and 50% for 14 d if CNS bleeding documented† |
Trauma with bleeding, surgery |
80-100 |
50 |
10-14 d |
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- Overview
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- Factor VIII Concentrates
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