Blood Tests 3 Flashcards
explain the mechanisms that prevent the normal flow of blood from clotting within blood vessels and ensure that coagulation only occurs at sites of injury
Endothelial Barrier: Endothelial cells that line the inner surface of blood vessels provide a natural barrier between the flowing blood and the underlying procoagulant proteins, such as collagen within the vessel wall. This barrier normally prevents blood from clotting inappropriately.
Nitric Oxide (NO): Endothelial cells secrete nitric oxide (NO), which serves as a potent vasodilator. Nitric oxide relaxes the smooth muscle in the walls of blood vessels, leading to vasodilation. This helps maintain normal blood flow and prevents clot formation within the vessels.
Prostacyclin: Endothelial cells also secrete prostacyclin, which is another powerful vasodilator. Prostacyclin helps inhibit platelet aggregation and the formation of blood clots. It further promotes vasodilation and maintains blood fluidity.
Injury-Induced Coagulation: Coagulation is a highly regulated process designed to occur primarily at sites of injury. When a blood vessel is injured, the exposed subendothelial surface and collagen initiate the coagulation cascade, leading to platelet activation and the formation of a stable blood clot to stop bleeding.
explain a patient’s history and evaluation for a bleeding disorder
HPC (History of Presenting Complaint):
Cause of Bleeding: Determine what event or circumstance led to the current bleeding episode. This information can help identify potential triggers or underlying causes.
Previous Bleeding Episodes: Inquire about any previous episodes of bleeding, whether they were spontaneous or related to trauma or procedures.
Duration of Bleeding: Note the duration of the current bleeding episode. Was it acute or chronic?
Response to Hemostatic Measures: Assess the patient’s response to any attempts to stop the bleeding, such as applying pressure, using topical hemostatic agents, or taking over-the-counter medications like antifibrinolytics.
Past Surgical History: Obtain a detailed surgical history, including any dental procedures, surgeries, or invasive medical interventions the patient has undergone.
Umbilical Cord Bleeding or Circumcision: Ask about any history of bleeding complications related to the umbilical cord at birth or circumcision procedures in males.
Hospitalization or Transfusion: Inquire whether the patient has previously been hospitalized or required blood transfusions due to bleeding episodes.
FHx (Family History):
Investigate whether there is a family history of bleeding disorders or a known genetic predisposition to bleeding. Identifying affected relatives can provide valuable insights into the possible hereditary nature of the patient’s bleeding tendencies.
Rx (Medications):
Document the patient’s current medications, including any anticoagulants like NOACs (novel oral anticoagulants), antiplatelet agents (such as aspirin), or other drugs that may affect blood coagulation.
explain a comprehensive medical assessment used to identify and evaluate various skin and bleeding disorders
Skin Findings:
Ecchymoses: These are large, bruise-like patches of purple or greenish discoloration on the skin, often caused by the leakage of blood into the surrounding tissues.
Senile Purpura: A common condition in older adults characterized by easily bruised and discolored skin, particularly on the arms and hands.
Petechiae: Small, red or purple pinpoint spots on the skin resulting from tiny blood vessel (capillary) bleeding.
Telangiectasia: The visible appearance of small, dilated blood vessels near the surface of the skin, often appearing as red or purplish lines or patterns.
Purpura: This refers to a condition where small blood vessels (capillaries) under the skin break, causing purple or red discoloration.
Bleeding Around Venepuncture Sites: Assess for signs of bleeding or bruising at sites where venipuncture (insertion of a needle into a vein) has occurred, which can indicate a bleeding tendency.
Systemic Evaluation:
Check for signs of systemic conditions such as liver disease (jaundice or signs of liver dysfunction), connective tissue disorders (e.g., skin and joint involvement), or renal disease (changes in skin color or texture).
Be vigilant for specific signs of conditions like scurvy, which include gum bleeding, joint pain, and skin changes.
Scars:
Examine any existing scars, as they can provide important historical information about previous injuries, surgeries, or medical conditions.
explain the distinction between the characteristics of bleeding due to thrombocytopenia or platelet defects and bleeding due to coagulation factor deficiencies or inhibitors
Bleeding Due to Thrombocytopenia or Platelet Defects:
Location of Bleeding: Primarily occurs into the skin and mucous membranes.
Timing: Bleeding is immediate and tends to happen right after an injury or trauma.
Examples: Petechiae, purpura, ecchymoses, gum bleeding, epistaxis (nosebleeds), and easy bruising are common manifestations of bleeding in thrombocytopenia or platelet function defects.
Bleeding Due to Coagulation Factor Deficiency or Inhibitor:
Location of Bleeding: Mainly occurs into deep tissues such as muscles and joints.
Timing: Bleeding may be delayed and not necessarily immediate following an injury.
Examples: Hemarthrosis (bleeding into the joints), muscle hematomas, and deep tissue bleeding are characteristic of bleeding associated with coagulation factor deficiencies or the presence of inhibitors.
explain the specific guidelines to ensure accurate and reliable test results when collecting blood samples for a coagulation screen
Blood Sample Collection:
Ensure that the blood sample is collected in the correct bottle or tube designed for coagulation testing.
The tube should be filled to the required volume or line, following the laboratory’s guidelines for sample volume.
Be mindful of the order in which you collect samples if using a vacuum system, as the first bottle may not be suitable for coagulation testing.
Essential Coagulation Tests:
Prothrombin Time (PT): This test measures the time it takes for blood to clot and assesses the extrinsic pathway of the coagulation cascade. It is used to monitor the function of factors I, II, V, VII, and X.
Activated Partial Thromboplastin Time (aPTT/PTT): The aPTT test evaluates the intrinsic pathway of the coagulation cascade and measures the time it takes for blood to clot. It helps assess factors VIII, IX, XI, and XII, among others.
Optional Coagulation Tests:
Thrombin Time (TT): TT measures the time it takes for fibrinogen in the blood to convert to fibrin. It can be useful in assessing fibrinogen function.
Fibrinogen Assay: This test specifically measures the concentration of fibrinogen in the blood, which is an essential component of the coagulation cascade.
Platelet Function Tests: Platelet function tests evaluate the ability of platelets to aggregate and participate in hemostasis.
Assays for Individual Factors or Antibodies: These tests assess the levels and activity of specific coagulation factors or the presence of antibodies that may interfere with the coagulation process.
50:50 (1:1) Mixing Study: A mixing study involves mixing the patient’s plasma with normal plasma in a 1:1 ratio to assess whether a coagulation factor deficiency is present.
International Normalized Ratio (INR): INR is often used to standardize PT results, especially for patients on anticoagulant therapy, such as warfarin. It ensures that PT results are consistent and comparable.
explain Prothrombin Time (PT)
Blood Sample Collection: A blood sample is collected from the patient using a special tube containing citrate anticoagulant. The anticoagulant prevents blood from clotting within the tube, ensuring that it remains in a liquid state for testing.
Reversal of Anticoagulant: In the laboratory, a mixture of chemicals is added to the blood sample to reverse the anticoagulant effect of citrate. This step is crucial to allow clot formation during the test.
Clot Formation Measurement: After the anticoagulant is neutralized, the blood sample is tested to determine the time it takes for a blood clot to form. This measurement is typically reported in seconds.
Normal PT Range: In a healthy individual, the PT results usually fall within a specific reference range, typically around 12 to 14 seconds. This reference range may vary slightly between laboratories.
Factor Deficiency Detection: An extended PT time (prolonged PT) suggests that one or more factors involved in the extrinsic and common coagulation pathways are deficient or not functioning properly. Factors that can cause a prolonged PT include factor VII, X, V, or II (prothrombin) deficiencies.
Clinical Significance: A prolonged PT can be indicative of various conditions, such as bleeding disorders, liver disease, vitamin K deficiency, or the use of anticoagulant medications. It may also be used to monitor patients receiving oral anticoagulant therapy, such as warfarin, to ensure that the treatment is within the desired therapeutic range.
explain Activated Partial Thromboplastin Time (aPTT)
Blood Sample Collection: A blood sample is collected from the patient using a tube that contains citrate anticoagulant. The anticoagulant ensures that the blood remains in a liquid state and doesn’t clot within the tube.
Reversal of Anticoagulant: In the laboratory, a mixture of chemicals, along with a partial thromboplastin reagent, is added to the blood sample to reverse the anticoagulant effect of citrate. This is a crucial step to enable clot formation during the test.
Clot Formation Measurement: After neutralizing the anticoagulant, the blood sample is tested to measure the time it takes for a blood clot to form. The result is typically reported in seconds.
Normal aPTT Range: In healthy individuals, the aPTT results generally fall within a specific reference range, which is typically between 30 and 40 seconds. The reference range may vary slightly depending on the laboratory and the reagents used.
Factor Deficiency Detection: A prolonged aPTT time (prolonged aPTT) indicates that one or more factors associated with the intrinsic and common coagulation pathways are deficient or not functioning correctly. Factors that can cause a prolonged aPTT include XII, XI, IX, VIII, X, V, or II (prothrombin) deficiencies.
Clinical Significance: A prolonged aPTT may suggest various conditions, including hemophilia, von Willebrand disease, or the presence of specific factor deficiencies. It can also be used to monitor patients receiving therapy with anticoagulants or as part of a preoperative assessment.
name a mnemonic to remember the differences between the Prothrombin Time (PT) and the Activated Partial Thromboplastin Time (aPTT/PTT) coagulation tests
PT (Prothrombin Time):
“Play Tennis Externally”
Associated with “extrinsic” factors.
Measures the extrinsic pathway of the coagulation cascade.
Evaluates factors VII, X, V, II (prothrombin), and the common pathway.
Often used to monitor warfarin therapy and assess the clotting cascade’s extrinsic components.
aPTT/PTT (Activated Partial Thromboplastin Time):
“Play Table Tennis Indoors”
Associated with “intrinsic” factors.
Measures the intrinsic and common pathways of coagulation.
Evaluates factors XII, XI, IX, VIII, X, V, II (prothrombin), and the common pathway.
Used to assess disorders related to intrinsic coagulation factors and to monitor heparin therapy.
A 14-month-old boy presents to the ED with an intramuscular haematoma after falling over in a playground. He had no history of bleeding from minor cuts or abrasions. There was no family history of bleeding disorders. Blood tests included coagulation:
PT 11.9 s (10.0 - 14.0)
APTT 102.3 s (32.0 - 42.0)
TT 9.3 s (9.0 - 11.0)
Fibrinogen 3.8g /L (1.5 - 4.0)
Plt count 250 x 109 /L (150 - 400)
APTT 1:1 mix 38.0s
The blood test results for the 14-month-old boy with an intramuscular hematoma indicate a prolonged Activated Partial Thromboplastin Time (aPTT), which may be indicative of a coagulation factor deficiency or abnormality in the intrinsic coagulation pathway. Let’s break down the test results:
Prothrombin Time (PT): The PT result is within the normal range, which suggests that the extrinsic coagulation pathway is functioning properly. This is reflected in the normal PT time of 11.9 seconds.
Activated Partial Thromboplastin Time (aPTT): The aPTT result is significantly prolonged at 102.3 seconds (normal range: 32.0 - 42.0 seconds). This prolonged aPTT indicates an issue in the intrinsic and common coagulation pathways.
Thrombin Time (TT): The TT result is within the normal range, which suggests that the conversion of fibrinogen to fibrin is occurring at the expected rate. The normal TT time of 9.3 seconds is consistent with appropriate fibrinogen function.
Fibrinogen: The fibrinogen level is within the normal range at 3.8 g/L (normal range: 1.5 - 4.0 g/L), indicating that the patient’s fibrinogen concentration is appropriate.
Platelet Count (Plt count): The platelet count is within the normal range at 250 x 10^9/L (normal range: 150 - 400 x 10^9/L), suggesting normal platelet function.
APTT 1:1 Mix: The APTT mixing study result is 38.0 seconds, which is within the normal range. This test involves mixing the patient’s plasma with normal plasma in a 1:1 ratio to determine whether the prolonged aPTT is due to a factor deficiency or inhibitor.
The significantly prolonged aPTT suggests that there may be a deficiency or abnormality in one of the intrinsic coagulation factors (e.g., factors VIII, IX, XI, XII) or the presence of an inhibitor affecting the intrinsic pathway. Further evaluation and specific coagulation factor assays are necessary to identify the exact factor deficiency or abnormality and determine the underlying cause of the prolonged aPTT. Given the clinical presentation, a pediatric hematologist may be consulted to manage and diagnose the coagulation disorder in this child.
explain the patient’s blood test results
Normal PT: The normal Prothrombin Time (PT) result rules out deficiencies or inhibitors of factors in the extrinsic and common coagulation pathways. This also excludes the presence of anticoagulants that affect PT, as you mentioned.
Normal Fibrinogen and TT: The normal Fibrinogen and Thrombin Time (TT) results indicate that there are no inhibitors or anticoagulants affecting these specific aspects of the coagulation cascade.
Normal Platelet Count: While the platelet count is normal, it’s important to consider the possibility of a functional platelet defect, which may not be reflected in the platelet count alone.
Normal 1:1 Test: The normal result of the 1:1 test confirms that there are no inhibitors affecting the clotting factors in the intrinsic and common coagulation pathways.
Given the blood test results and the clinical presentation of the patient with an intramuscular hematoma, the significantly prolonged aPTT is likely due to a deficiency or abnormality in one of the intrinsic coagulation factors (e.g., factors VIII, IX, XI, XII) rather than the presence of inhibitors or anticoagulants. Further diagnostic tests, such as specific coagulation factor assays, are necessary to identify the exact factor deficiency and determine the underlying cause of the prolonged aPTT. A pediatric hematologist or coagulation specialist can provide the expertise needed to manage and diagnose this coagulation disorder in the child.
