Test ID: HEPN
Heparin Anti-Xa Assay, Plasma
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Measuring heparin concentration:
-In patients treated with low molecular weight heparin preparations
-In presence of prolonged baseline activated partial thromboplastin time (APTT) (eg, lupus anticoagulant, "contact factor" deficiency, etc.)
-When unfractionated heparin dose needed to achieve desired APTT prolongation is unexpectedly higher (>50%) than expected
Method Name A short description of the method used to perform the test
Chromogenic Method on STA-R Evolution
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Anti-Xa
Fragmin (Dalteparin)
Heparin Anti-Xa Assay, Plasma
Lovenox (Enoxaparin)
Low-Molecular Weight Heparin Assay
Unfractionated Heparin Assay
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Specimen Type: Platelet-poor plasma
Collection Container/Tube:
Preferred: Light-blue top (3.2% sodium citrate at 9:1 ratio)
Acceptable: Light-blue top (3.8% sodium citrate at 9:1 ratio)
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions: Spin down, remove plasma, and spin plasma again.
Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
Forms: If not ordering electronically, submit a General Request Form (Supply T239) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Plasma Na Cit | Frozen | 30 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Heparins are sulphated glycosaminoglycans that inactivate thrombin, factor Xa, and several other coagulation factors; act by enhancing activity of the plasma coagulation inhibitor, antithrombin III (AT III); prolong the activated partial thromboplastin time (APTT); of low molecular weight heparin have minimal effect on the APTT, and require an alternative method, such as the anti-Xa assay, to monitor therapy.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =18 years
UFH therapeutic range: 0.30-0.70 IU/mL
LMWH therapeutic range:
0.50-1.00 IU/mL for twice daily dosing
1.00-2.00 IU/mL for once daily dosing
(sample obtained 4-6 hours following subcutaneous injection)
> or =8 weeks-17 years
UFH therapeutic range: 0.30-0.70 IU/mL
LMWH therapeutic range: 0.50-1.00 IU/mL (sample obtained 4-6 hours following subcutaneous injection)
LMWH prophylactic range: 0.10-0.30 IU/mL
<8 weeks
Reference values have not been established for patients who are less than 8 weeks of age.
Interpretation Provides information to assist in interpretation of the test results
Therapeutic ranges:
Adults > or =18 years
-Standard heparin (UFH): 0.30 to 0.70 IU/mL
-Low molecular weight heparin (LMWH): 0.50 to 1.00 IU/mL for twice daily dosing (specimen drawn 4-6 hours following subcutaneous injection) or 1.00 to 2.00 IU/mL for once daily dosing (specimen drawn 4-6 hours following subcutaneous injection)
Children <8 weeks
-Standard heparin (UFH): 0.30 to 0.70 IU/mL
-LMWH: 0.50 to 1.00 IU/mL (specimen drawn 4-6 hours following subcutaneous injection)
-LMWH (prophylactic): 0.10 to 0.30 IU/mL
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test should not be used for routine monitoring of unfractionated heparin (UFH) therapy except as indicated above. The activated partial thromboplastin time (APTT) test is routinely used to monitor UFH therapy.
This is not a test for the presence of inhibitors directed against factor X (FX).
Plasma specimen must be depleted of platelets by repeat centrifugation before freezing.
During freezing and thawing, residual platelets in plasma release platelet factor 4, possibly causing falsely-low heparin levels.
Not useful for monitoring therapy with the heparinoid "danaparoid."
Very low endogenous antithrombin III (AT III) levels might result in spuriously-low results.
Antibodies to bovine FX or AT III can interfere with assay (very rare).
Lipemia, icterus, and hemolysis may interfere with color detection and give inaccurate results.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Marci CD, Prager D: A review of the clinical indications for the plasma heparin assay. Am J Clin Pathol 1993;99:546-550
2. Houbouyan L, Boutiere B, Contant G, et al: Validation of analytical hemostasis systems: measurement of anti-Xa activity of low-molecular-weight-heparins. Clin Chem 1996;42:1223-1230
3. Jeske W, Messmore HL Jr, Fareed J: Pharmacology of heparin and oral anticoagulants. In Thrombosis and Hemorrhage. Second edition. Edited by J Loscalzo, AI Schafer. Baltimore, MA, Williams and Wilkins, 1998, pp 1193-1204
4. Monagle P, Michelson AD, Bovill E, Andrew M: Antithrombotic therapy in children. CHEST 2001;119:344-370
5. Fraser G, McKenna J: Monitoring low molecular weight heparins with antiXa activity: house of cards or firm foundation? Hospital Pharmacy 2003;38:202-211
6. Nutescu EA, Spinler SA, Wittkowsky A, Dager WE: Low-molecular-weight heparins in renal impairment and obesity: available evidence and clinical practice recommendations across medical and surgical settings. Ann Pharmacother 2009;43:1064:1083
Method Description Describes how the test is performed and provides a method-specific reference
Residual free factor Xa is measured in plasma by chromogenic substrate assay after addition of bovine antithrombin III (AT III) and factor Xa, which forms an inactive factor Xa-AT III-heparin complex.(Meyers BJ, Plumhoff EA, Gastineau DA, et al: A heparin assay system for measuring unfractionated heparin and low molecular weight heparin using the same standard curve. Blood 1998;92:123b)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
85520
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| HEPN | Heparin Anti-Xa Assay, P | In Process |
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