Flashcards in Investigations Deck (27)
What is the practical approach to a bleeding patient?
- FBC with platelet count
- Prothrombin time (PT)
- Activated Partial Thromboplastin Time (APTT)
What does mixture of patient and normal plasma show?
50/50 mix will show:
- Corrects = deficiency
- No correction = inhibitor
What clotting factors affect APTT?
VIII, IX, XI, XII and vW factor
What is the diagnostic triad of clotting disorders?
1. Personal history of bleeding
2. FH of bleeding
3. Supportive laboratory tests
What will FBC and clotting tests show you?
- Hb, haematocrit and WBC
- Platelets (normal 150-400 x10^9/L)
- Prothrombin time (PT) - normal 10-12 sec (tests VII, measures extrinsic pathway)
- Activated Partial Thromboplastin Time (APTT) (normal 20-30 secs) - measures intrinsic pathway
- APTT 50:50
What conditions could the patient have if the APTT returns to normal after the 50:50 test?
- Factor VIII deficiency (haemophilia A)
- Factor IX deficiency (haemophilia B)
What factors are measured in the extrinsic pathway?
- Tissue factor (TF) to VIIa to Xa
What factors are measured in the intrinsic pathway?
- IX-XII to VIIIa to Xa
- PK + HK > XI x XII
What are the causes of prolonged PT?
- Warfarin (most common)
- VII (2nd most common)
what are the causes of APTT prolonged?
- XII (but no bleeding)
- vW disease
What are the causes of prolonged PT and APTT?
- Vitamin K deficiency and low fibrinogen - liver disease, malabsorption
- DIC (disseminated intravascular coagulation) + low fibrinogen >> FDPs, d-dimers raised, low platelets, red cell fragments
- Heparin toxicity (normal fibrinogen)
- Rarely (normal fibrinogen) - deficiencies of factor V or X
What are the vitamin K dependent factors?
II, VII, IX, X, protein C, protein S
What are the platelet tests?
- PFA - screen of platelet function
- Specialist tests - aggregation + nucleotide release, glycoproteins, molecular genetics (MYH9), bone marrow
What are the tests for clot stability?
- Euglobin clot lysis
- Factor XIII assay
What tests are used for VW screen?
- Factor VIII (normal 50-150iu/dl)
- VW antigen (normal 50-150iu/dl)
- VW activity (normal 50-150 iu/dl)
How is type 1 and 2 VW disease differentiated?
Ratio of VWF activity : VWF antigen
If ratio is >0.6 = type 1 and if <0.6 = type 2
What are the typical ECG findings of PE?
- Sinus tachycardia
- May see AF or evidence of right heart strain (right axis deviation or RBBB) with classical S1 Q3 T3 pattern
What would an ABG show for PE?
Hypoxia of T1 respiratory failure
What tests are done for PE and DVT?
- If Wells score is low then do d-dimer (detects fibrin breakdown products), if result is normal or negative DVT and PE can be excluded
- If Wells score low and d-dimer positive then further imaging.
- If Wells score is high probability then recommend going for highly specific imaging tests
What are differentials for a positive d-dimer test?
- Pregnancy (Wells score doesn't apply)
What imaging tests are done for DVT and PE?
- DT - US doppler scan
- PE - CT pulmonary angiogram (CTPA)
What are the highly specific imaging tests for DVT and PE?
U+E, ABG, LFT, CXR (exclude other causes such as pneumothorax), clotting screen (baseline clotting), FBC, CTPA, ECG
What would a CXR for a PE show?
- Reduced vascular markings/oligemia
- Dilated pulmonary artery
- Pleural effusion
- Exclude pneumothorax
Who should a V/Q test be done on?
Pregnant women as CTPA is not good
What does an ABG show in DVT/PE patients?
- Normal in 20%
- Decreased pO2, decreased pCO2, increased pH due to hyperventilation and poor gas exchange > respiratory alkalosis
- Leads to type 1 respiratory failure as there is a ventilation/perfusion mismatch - parts of lungs getting air but no blood flow for gas exchange
- This means not enough oxygen in blood > respiratory alkalosis as their RR is high so CO2 diffuses more freely across alveolar membranes than O2.
What are the results for tests for VW?
- Increased APTT
- Increased bleeding time
- Decreased factor VIIIc (clotting activity)