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Useful For
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To detect antibodies against the Heparin/PF4 complex in patients on Heparin thereapy.
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Method name and description
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Automated.
HemosIL HIT-Ab(PF4-H) is a latex-enhanced immunoturbidimetric assay for the detection of anti-PF4-H, commonly associated with HIT. The latex reagent is a suspension of polystyrene particles, coated with a monoclonal antibody against PF4-H. The competitive agglutination reaction occurs when a complex of PF4 and PVS (polyvinyl sulfonate, a compound similar to Heparin) is mixed with the latex and patient sample. Anti-PF4-H in a positive sample will bind to the complex, thereby inhibiting agglutination, while the absence of anti-PF4-H will allow the complex to bind to the latex, thereby allowing agglutination.
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Reporting name
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Heparin Induced Thrombocytopenia (HIT)
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Clinical information
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There are two distinct type of Heparin-induced thrombocytopenia (HIT) :
1- type I HIT which is nonimmune heparin-associated thrombocytopenia (HAT). This is a common benign thrombocytopenia, characterized by a mild decrease of the platelet count, occurring early in the course of treatment with heparin, especially intravenous UFH. It does not progress and may resolve spontaneously despite continuation of heparin therapy.
2 -Type II HIT (immune heparin-associated thrombocytopenia) caused by antibodies directed against heparin/platelet factor 4 complexes. A serious immune-mediated syndrome occurs in 1%- 5% of patients treated with UFH, with delayed onset, typically between days 5 and 10 of UFH therapy. In patients previously treated with heparin (within the preceding 3-6 months), thrombocytopenia can develop rapidly (within 24 hours) after heparin re-exposure. In Type II HIT, the platelet count typically decreases by 40% to 50% from baseline.
Immune HIT is clinically important, because of the high risk for development of arterial or venous thrombosis.
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Specimen type / Specimen volume / Specimen container
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Plasma Na Cit. Platelet-poor plasma. Specimen Volume: 2.7 ml. Container/Tube: Light-blue top .
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Collection instructions / Special Precautions / Timing of collection
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Sample collected in HMC facilities/others and transported to the lab within 1hour :
• Collect sample into light blue-top (sodium citrate).
• Tubes must be filled to within +/- 10% of their proper volume, to provide a 9:1 ratio of blood to citrate.
2- Samples collected in HMC facilities / others and which are expected not to reach the lab within 1hour:
• Centrifuge the whole blood and carefully remove the plasma by pipette not by decanting and send the plasma in a temperature-controlled environment (18-25ºC ) within one hour of centrifugation.
• If the transportation of the plasma can’t be within a maximum of 2hour , prepare platelet-poor plasma as follow:
A: Re-centrifuge plasma again.
B: Remove the top portion of plasma leaving approximately 250 mcL in the bottom to discard.
C: The double-centrifuged plasma should be aliquoted (0.5 to 1 mL per aliquot) into labeled plastic tubes. The number of tests ordered will determine the aliquots needed.
D: Freeze immediately at -20 ºC or below .
E: Specimens must arrive frozen.
3- Sample for Platelets function studies (Platelets function assay) , Citrated whole blood should reach HMC within a maximum of 1-2 hours of collection.
4- For heparin monitoring, follow the above mentioned steps.
5- Consider patient HCT %. , if HCT is >55%, the volume of anticoagulant in the tube must be adjusted by the referring lab, as per the below table shows the volume of citrate (µL) to be removed from common sizes of coagulation specimen tubes prior to specimen collection. After removal of the specified volume of citrate, enough blood is added to fill the tube to the ideal volume.
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Hematocrit %
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Volume to be removed, µL
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2.7 ml Tube
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1.0 ml Tube
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56
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50
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20
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57
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50
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20
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58
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60
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20
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59
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60
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20
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60
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70
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30
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61
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70
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30
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62
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80
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30
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63
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80
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30
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64
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90
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30
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65
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90
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30
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66
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100
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40
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67
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100
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40
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68
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110
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40
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69
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110
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40
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70
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120
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40
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71
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120
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40
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72
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130
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50
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73
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130
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50
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74
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140
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50
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75
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140
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50
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76
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150
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50
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77
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150
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60
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78
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160
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60
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79
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160
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60
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80
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170
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60
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Relevant clinical information to be provided
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Type of Heparin given must be clearly indicated (whether UFH or LMWH) .
Patient/family history of bleeding disorder. History of anticoagulant therapy.
History of chronic diseases
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Storage and transport instructions
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Specimen Rejection Criteria
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Specimens with no label or missing required identification
Broken, leaking or contaminated specimen
Clotted samples
Under-filled or overfilled sample tubes.
Wrong sample container sample received
Improper specimen transport temperature (e.g. like specimens which are needed to be sent on ice)
Old specimen (test-dependent)
Grossly Hemolyzed sample (test-dependent)
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Biological reference intervals and clinical decision values
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Reference range in normal /untreated population with heparin:0.0 U/mL.
On heparin treated patient samples, HemosIL HIT-Ab(PF4-H) results equal or higher than 1.0 U/mL may indicate the presence of HIT antibodies.
Although a positive result obtained using this assay may indicate the presence of heparin-associated antibodies, a positive result DOES NOT CONFIRM the diagnosis of HIT. Some patients may have naturally occurring antibodies to PF4.
The assay results should be used with other information, including the clinical context, in forming a diagnosis.
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Factors affecting test performance and result interpretation
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HIT-Ab (PF4-H) results on the ACL TOP® Family are not affected by
- Hemoglobin up to 495 mg/dL,
- Bilirubin up to 18 mg/dL, Triglyceride up to 375 mg/dL,
- Rheumatoid Factor up to 1000 IU/mL,
- Human anti-mouse antibodies (HAMA) up to 1 µg/mL.2
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Turnaround time / Days and times test performed / Specimen retention time
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