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Hemophilia B Workup

  • Author: Robert A Zaiden, MD; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
Updated: Mar 11, 2016

Approach Considerations

Laboratory studies for suspected hemophilia B include a complete blood cell count, coagulation studies, and a factor IX (FIX) assay. Never delay indicated coagulation correction pending diagnostic testing.

On the hemoglobin/hematocrit, expect normal or low values. Expect a normal platelet count. On coagulation studies, the bleeding time and prothrombin time (which assesses the extrinsic coagulation pathway) 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 FIX assays, levels are compared with a normal pooled-plasma standard, which is designated as having 100% activity or the equivalent of FIX U/mL. Normal values are 50-150%. Values in hemophilia are as follows:

  • Mild - Greater than 5%
  • Moderate - 1-5%
  • Severe - Less than 1%

Spontaneous bleeding complications are severe in individuals with undetectable activity (< 0.01 U/mL), moderate in individuals with activity (2-5% normal), and mild in individuals with factor levels greater than 5%.

Usually, von Willebrand factor (vWF) levels are also measured. The combination of low FVIII and low vWF may indicate vWF deficiency as the primary diagnosis.

Because FIX is a large molecule that does not cross the placenta, the diagnosis can be made at birth with quantitative assay of coagulation factors in the cord blood. However, early diagnosis of FIX deficiency is complicated by the physiologic reduction of vitamin K–dependent factors in young infants. In term and healthy premature neonates, FIX values are low (20-50% of the normal level), due to hepatic immaturity. levels rise to normal after 6 months of age. FVIII levels are normal during that period of life.

In patients with an established diagnosis of hemophilia B, laboratory evaluations include periodic screening for the presence of FIX inhibitor and screening for transfusion-related or transmissible diseases such as hepatitis and HIV. This may be less important in populations who receive only recombinant product.[#WorkupImagingStudies]

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 anatomic location of involvement.

Head CT scans without contrast are used to assess for spontaneous or traumatic intracranial hemorrhage. Perform magnetic resonance imaging 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 FIX inhibitor is clinically important when bleeding is not controlled after adequate amounts of factor concentrate are infused during a bleeding episode. 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.

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 10 BU is a high titer. The distinction is clinically significant, as patients with low-titer inhibitors may respond to higher doses of FVIII concentrate.


Carrier Testing and Fetal Testing

FIX level is often normal in FIX carriers. When the specific FIX gene mutation is known, direct genetic testing provides accurate results. 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 FIX mutations.

For fetal testing, if the mutation is known, then RFLP can be performed on chorionic villous or amniocentesis samples. If the mutation is not known, gene sequencing can be performed.



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 are 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.[5] For discussion of the 5-stage Arnold-Hilgartner classification of hemophilic arthropathy, see Imaging in Musculoskeletal Complications of Hemophilia

Contributor Information and Disclosures

Robert A Zaiden, MD Assistant Professor, Division of Hematology/Oncology, Department of Medicine, University of Florida at Jacksonville College of Medicine

Robert A Zaiden, MD is a member of the following medical societies: American College of Physicians, American Society of Clinical Oncology

Disclosure: Nothing to disclose.

Chief Editor

Srikanth Nagalla, MBBS, MS, FACP Director, Clinical Hematology, Cardeza Foundation for Hematologic Research; Assistant Professor of Medicine, Division of Hematology, Associate Program Director, Hematology/Medical Oncology Fellowship, Assistant Program Director, Internal Medicine Residency, Jefferson Medical College of Thomas Jefferson University

Srikanth Nagalla, MBBS, MS, FACP is a member of the following medical societies: American Society of Hematology, Association of Specialty Professors

Disclosure: Nothing to disclose.


Dimitrios P Agaliotis, MD, PhD, FACP Consulting Staff, Department of Medicine, Baptist Health System

Disclosure: Nothing to disclose.

Jeffrey L Arnold, MD, FACEP Chairman, Department of Emergency Medicine, Santa Clara Valley Medical Center

Jeffrey L Arnold, MD, FACEP is a member of the following medical societies: American Academy of Emergency Medicine and American College of Physicians

Disclosure: Nothing to disclose.

Emmanuel C Besa, MD Professor, Department of Medicine, Division of Hematologic Malignancies and Hematopoietic Stem Cell Transplantation, Kimmel Cancer Center, Jefferson Medical College of Thomas Jefferson University

Emmanuel C Besa, MD is a member of the following medical societies: American Association for Cancer Education, American College of Clinical Pharmacology, American Federation for Medical Research, American Society of Clinical Oncology, American Society of Hematology, and New York Academy of Sciences

Disclosure: Nothing to disclose.

Gary D Crouch, MD Associate Professor, Program Director of Pediatric Hematology-Oncology Fellowship, Department of Pediatrics, Uniformed Services University of the Health Sciences

Gary D Crouch, MD is a member of the following medical societies: American Academy of Pediatrics and American Society of Hematology

Disclosure: Nothing to disclose.

Brendan R Furlong, MD Clinical Chief, Department of Emergency Medicine, Georgetown University Hospital.

Brendan R Furlong is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Mary A Furlong, MD Associate Professor and Program/Residency Director, Department of Pathology, Georgetown University School of Medicine

Mary A Furlong, MD is a member of the following medical societies: United States and Canadian Academy of Pathology

Disclosure: Nothing to disclose.

William G Gossman, MD Associate Clinical Professor of Emergency Medicine, Creighton University School of Medicine; Consulting Staff, Department of Emergency Medicine, Creighton University Medical Center

William G Gossman, MD is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.

Lawrence F Jardine, MD, FRCPC Associate Professor, Department of Pediatrics, Schulich School of Medicine and Dentistry, University of Western Ontario; Head, Section of Pediatric Hematology and Oncology, Children's Hospital of Western Ontario; Associate Scientist, Child Health Research Institute

Lawrence F Jardine, MD, FRCPC is a member of the following medical societies: American Society of Hematology, American Society of Pediatric Hematology/Oncology, Canadian Medical Protective Association, Children's Oncology Group, College of Physicians and Surgeons of Ontario, Hemophilia and Thrombosis Research Society, Ontario Medical Association, and Royal College of Physicians and Surgeons of Canada

Disclosure: Baxter Honoraria Consulting; Bayer Honoraria Consulting; Novartis Honoraria Speaking and teaching

Adonis Lorenzana, MD Consulting Staff, Department of Pediatric Oncology, St John Hospital and Medical Center

Adonis Lorenzana, MD is a member of the following medical societies: American Academy of Pediatrics and American Society of Pediatric Hematology/Oncology

Disclosure: Nothing to disclose.

Saduman Ozturk, PA-C Physician Assistant, Bone Marrow Transplant Center, Florida Hospital Cancer Institute

Disclosure: Nothing to disclose.

Ronald A Sacher, MB, BCh, MD, FRCPC Professor, Internal Medicine and Pathology, Director, Hoxworth Blood Center, University of Cincinnati Academic Health Center

Ronald A Sacher, MB, BCh, MD, FRCPC is a member of the following medical societies: American Association for the Advancement of Science, American Association of Blood Banks, American Clinical and Climatological Association, American Society for Clinical Pathology, American Society of Hematology, College of American Pathologists, International Society of Blood Transfusion, International Society on Thrombosis and Haemostasis, and Royal College of Physicians and Surgeons of Canada

Disclosure: Glaxo Smith Kline Honoraria Speaking and teaching

Hadi Sawaf, MD Director, Pediatric Hematology Oncology, Van Elslander Cancer Center; Clinical Assistant Professor, Wayne State University School of Medicine

Hadi Sawaf, MD is a member of the following medical societies: American Academy of Pediatrics, American Society of Clinical Oncology, and American Society of Hematology

Disclosure: Nothing to disclose.

Karen Seiter, MD Professor, Department of Internal Medicine, Division of Oncology/Hematology, New York Medical College

Karen Seiter, MD is a member of the following medical societies: American Association for Cancer Research, American College of Physicians, and American Society of Hematology

Disclosure: Novartis Honoraria Speaking and teaching; Novartis Consulting fee Speaking and teaching; Ariad Honoraria Speaking and teaching; Celgene Honoraria Speaking and teaching

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

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Coagulation Cascade
Table 1. Severity, Factor Activity, and Hemorrhage Type
Classification Factor Activity, % Cause of Hemorrhage
Mild >5-40 Major trauma or surgery
Moderate 1-5 Mild-to-moderate trauma
Severe < 1 Spontaneous, hemarthrosis
Table 2. General Guidelines for Factor Replacement for the Treatment of Bleeding in Hemophilia B
Indication or Site of Bleeding Factor level Desired, % FIX Dose, IU/kg* Comment
Severe epistaxis; mouth, lip, tongue, or dental work 20-50 20-50 Consider aminocaproic acid (Amicar), 1-2 d
Joint (hip or groin) 40 40 Repeat transfusion in 24-48 h
Soft tissue or muscle 20-40 40 No therapy if site small and not enlarging (transfuse if enlarging)
Muscle (calf and forearm) 30-40 40 None
Muscle deep (thigh, hip, iliopsoas) 40-60 40-60 Transfuse, repeat at 24 h, then as needed
Neck or throat 50-80 50-80 None
Hematuria 40 40 Transfuse to 40% then rest and hydration
Laceration 40 40 Transfuse until wound healed
GI or retroperitoneal bleeding 60-80 60-80 None
Head trauma (no evidence of CNS bleeding) 50 50 None
Head trauma (probable or definite CNS bleeding, eg, headache, vomiting, neurologic signs) 100 100 Maintain peak and trough factor levels at 100% and 50% for 14 d if CNS bleeding documented
Trauma with bleeding, surgery 80-100 100 10-14 d
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