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Activated Partial Thromboplastin Time (APTT) : 1000084
MessageThe plasma aliquot must remain frozen. Freeze thaw cycle will adversely affect specimen integrity. CRITICAL FROZEN: Separate specimens must be submitted when multiple tests are ordered.
Test Code
APTT or 1000084
Alias/See Also
APTT; Partial Thromboplastin Time, Activated; PTT
CPT Codes
85730
Instructions
Blue top tube, 3.2% sodium citrate.
• Obtain venous blood by clean venipuncture. Avoid slow-flowing draws and/or traumatic venipunctures as either of these may result in an activated or clotted specimen. Do not use needles smaller than 23 gauge. Do not leave the tourniquet on for an extended length of time before drawing the sample.
• A pilot tube (non-additive or light blue tube) before drawing coagulation specimens in light blue vacuum tubes is only necessary when using a butterfly blood collection set as this will cause reduced draw volume in the first tube. Discard the pilot tube.
• Fill light blue tubes as far as vacuum will allow and mix by gentle inversion. Exact ratio of nine parts blood to one part anticoagulant must be maintained. Inadequate filling of the sample tube will alter this ratio and may lead to inaccurate results. Patients who have hematocrit values above 55 percent should have the anticoagulant adjusted to maintain the 9:1 ratio. Use the following formula to determine the amount of anticoagulant to use: [(100 – Hct) / (595 – Hct) ]* total volume = amount of anticoagulant required.
• After collecting the blood, examine the tube to ensure that it is filled to within 90% of the fill line.
• Note: Specimens containing heparin should not be used for coagulation studies. If possible, stop heparin therapy before the draw to avoid contamination. Heparin interferes with most clotting assays. If heparinized line must be used to obtain the sample, flush line with 5mL saline and discard the first 5 mL of blood drawn into a syringe, or 6 “dead space” volumes of the line.
• Obtain venous blood by clean venipuncture. Avoid slow-flowing draws and/or traumatic venipunctures as either of these may result in an activated or clotted specimen. Do not use needles smaller than 23 gauge. Do not leave the tourniquet on for an extended length of time before drawing the sample.
• A pilot tube (non-additive or light blue tube) before drawing coagulation specimens in light blue vacuum tubes is only necessary when using a butterfly blood collection set as this will cause reduced draw volume in the first tube. Discard the pilot tube.
• Fill light blue tubes as far as vacuum will allow and mix by gentle inversion. Exact ratio of nine parts blood to one part anticoagulant must be maintained. Inadequate filling of the sample tube will alter this ratio and may lead to inaccurate results. Patients who have hematocrit values above 55 percent should have the anticoagulant adjusted to maintain the 9:1 ratio. Use the following formula to determine the amount of anticoagulant to use: [(100 – Hct) / (595 – Hct) ]* total volume = amount of anticoagulant required.
• After collecting the blood, examine the tube to ensure that it is filled to within 90% of the fill line.
• Note: Specimens containing heparin should not be used for coagulation studies. If possible, stop heparin therapy before the draw to avoid contamination. Heparin interferes with most clotting assays. If heparinized line must be used to obtain the sample, flush line with 5mL saline and discard the first 5 mL of blood drawn into a syringe, or 6 “dead space” volumes of the line.
Transport Container
Ambient Whole Blood: The blue top tube must be kept at room temperature. Do not refrigerate or freeze. If the specimen will not be tested in the laboratory within 24 hours of collection, then the tube must be centrifuged and plasma must be submitted frozen per instructions below.
Frozen Plasma: Centrifuge the blue top tube at a rate of speed to yield platelet poor plasma (<10,000 /uL), immediately remove only the top two-thirds of the platelet-poor plasma from the specimen using a plastic-transfer pipet (use of glass-transfer pipets may result in activation and/or clotting of the plasma) and transfer citrated plasma (Min. 0.5 mL) into a standard transport tube, and freeze the aliquot.
Frozen Plasma: Centrifuge the blue top tube at a rate of speed to yield platelet poor plasma (<10,000 /uL), immediately remove only the top two-thirds of the platelet-poor plasma from the specimen using a plastic-transfer pipet (use of glass-transfer pipets may result in activation and/or clotting of the plasma) and transfer citrated plasma (Min. 0.5 mL) into a standard transport tube, and freeze the aliquot.
Transport Temperature
Whole blood: Ambient.
Plasma: Frozen.
Plasma: Frozen.
Specimen Stability
Whole blood: Ambient: 24 hours
Plasma after separation from cells: Ambient: 4 hours; Refrigerated: 4 hours; Frozen: 2 weeks
Plasma after separation from cells: Ambient: 4 hours; Refrigerated: 4 hours; Frozen: 2 weeks
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Tubes not filled within 90% of the fill line will be rejected by the lab.
Methodology
Clotting
Setup Schedule
Sunday - Saturday
Report Available
1 day
Limitations
This test has not been validated for monitoring unfractionated heparin therapy. For testing that is validated for this type of therapy, please refer to Heparin, Anti-Xa, Unfractionated Assay (test code XAUNF or 1001022).
Reference Range
0 to <4 days: Not established
≥4 days to <7 months: 24.0 – 37.0 seconds
≥7 months to <18 years: 24.0 – 34.0 seconds
≥ 18 years old: 22.0 – 32.0 seconds
≥4 days to <7 months: 24.0 – 37.0 seconds
≥7 months to <18 years: 24.0 – 34.0 seconds
≥ 18 years old: 22.0 – 32.0 seconds
Clinical Significance
The Activated Partial Thromboplastin Time (aPTT) is a screening procedure for evaluating deficiencies in coagulation factors of the intrinsic coagulation pathway, including Factors VIII, IX, XI, XII, Fletcher Factor, and Fitzgerald Factor. Severe deficiencies of fibrinogen and Factors II, V, and X can also be detected by the aPTT. It is a useful and effective method for screening patients with a bleeding tendency, for evaluating the effect of therapy in procoagulant disorders, and as the basis for several specific coagulation factor assay procedures. The aPTT may also be used as a test for monitoring and regulating heparin therapy. The presence of nonspecific inhibitors, such as the Lupus anticoagulant, may prolong the aPTT, but this effect is variable and generally recognized as being related to the nature and level of the inhibitor as well as the aPTT reagent.
TEST PRINCIPLE:
The aPTT test consists of activation of the factors of the intrinsic coagulation pathway with the optimal amount of phospholipids and a surface activator. The addition of calcium ions triggers the coagulation process and the clotting time in seconds is measured.
LIMITATIONS:
aPTT testing encompasses the entire clotting process from contact activation to fibrin formation and is therefore more susceptible to variations than specific individual tests. The control and use of aPTT is therefore subject to inherent limitations. Control of plasma sample and storage conditions is strictly emphasized. Studies have shown that sample decomposition may occur more rapidly in stored samples that are not refrigerated. Extremely small plasma volumes prior to testing are to be avoided since pH changes in the plasma from physiological conditions may be encountered. Such changes may lead to the decomposition of plasma components of the coagulation system.
aPTT testing may be affected by a number of commonly administered drugs. Decrease in time of aPTT determination in conjugated estrogen therapy in males and oral contraceptive administration in females has been reported. Increase in the aPTT has been seen in diphenylhydantoin, heparin, warfarin, naloxone, and radiographic agent administration. Therapeutic doses of hirudin or other direct thrombin inhibitors may prolong clotting times. The condition of the specimen (e.g., hemolyzed, lipemic, parenteral feeding, etc.) may affect results.
Blood clotting factor deficiencies which should produce prolonged clotting times may be compensated for or made to appear normal by elevated levels of one or more different clotting factors. Similarly, the presence of active intermediates which would tend to reduce the clotting time may also mask conditions that would normally lead to prolongation of the aPTT. Mild or minor deficiencies in several factors may have an additive effect on increasing the aPTT. Variable aPTT results may be obtained in samples containing the Lupus anticoagulant. Unexpected abnormal aPTT results should always be followed by additional coagulation studies to determine the source of abnormal results.
TEST PRINCIPLE:
The aPTT test consists of activation of the factors of the intrinsic coagulation pathway with the optimal amount of phospholipids and a surface activator. The addition of calcium ions triggers the coagulation process and the clotting time in seconds is measured.
LIMITATIONS:
aPTT testing encompasses the entire clotting process from contact activation to fibrin formation and is therefore more susceptible to variations than specific individual tests. The control and use of aPTT is therefore subject to inherent limitations. Control of plasma sample and storage conditions is strictly emphasized. Studies have shown that sample decomposition may occur more rapidly in stored samples that are not refrigerated. Extremely small plasma volumes prior to testing are to be avoided since pH changes in the plasma from physiological conditions may be encountered. Such changes may lead to the decomposition of plasma components of the coagulation system.
aPTT testing may be affected by a number of commonly administered drugs. Decrease in time of aPTT determination in conjugated estrogen therapy in males and oral contraceptive administration in females has been reported. Increase in the aPTT has been seen in diphenylhydantoin, heparin, warfarin, naloxone, and radiographic agent administration. Therapeutic doses of hirudin or other direct thrombin inhibitors may prolong clotting times. The condition of the specimen (e.g., hemolyzed, lipemic, parenteral feeding, etc.) may affect results.
Blood clotting factor deficiencies which should produce prolonged clotting times may be compensated for or made to appear normal by elevated levels of one or more different clotting factors. Similarly, the presence of active intermediates which would tend to reduce the clotting time may also mask conditions that would normally lead to prolongation of the aPTT. Mild or minor deficiencies in several factors may have an additive effect on increasing the aPTT. Variable aPTT results may be obtained in samples containing the Lupus anticoagulant. Unexpected abnormal aPTT results should always be followed by additional coagulation studies to determine the source of abnormal results.
Performing Laboratory
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