A patient is receiving anticoagulant heparin sulphate therapy. Which of the following lab report should be monitored?

Appeared in: NORCET 5 Prelims - Sept 2023 (Shift-1)

Explanation

Partial Thromboplastin Time (PTT), and more specifically Activated PTT (aPTT), is the standard laboratory test used to monitor the therapeutic effectiveness of heparin.
Heparin primarily affects the intrinsic and common pathways of the coagulation cascade, and the aPTT test directly measures the functionality of these pathways.
The therapeutic goal for a patient on heparin is to maintain an aPTT level that is 1.5 to 2.5 times the baseline control value, which typically corresponds to a range of 45 to 70 seconds.

Option A: This is an older, less sensitive, and less precise test for monitoring heparin therapy. It provides a general measure of clotting but is not the standard of care.
Option C: This test measures the extrinsic and common coagulation pathways, which are primarily affected by warfarin, not heparin.
Option D: This test measures the oxygen-carrying capacity of red blood cells and does not assess the blood's clotting ability or the drug's therapeutic effect.

Visual 1: Flowchart - The coagulation cascade, highlighting the intrinsic pathway (monitored by aPTT and affected by heparin) and the extrinsic pathway (monitored by PT and affected by warfarin).
Visual 2: Table - A comparison chart detailing the differences between Heparin and Warfarin, including their mechanism of action, route of administration, onset, antidote, and the specific laboratory test used for monitoring (aPTT vs. PT/INR).

Clinical Relevance

Nursing practice connection: Use the key finding related to Laboratory Monitoring of Anticoagulant Therapy to guide bedside assessment, documentation, and the next nursing action.
Accurate monitoring of heparin with aPTT is critical for patient safety, preventing both thrombotic events (from under-dosing) and life-threatening hemorrhage (from over-dosing).
Nurses are responsible for ensuring aPTT levels are drawn at appropriate intervals (e.g., 4-6 hours after initiation or dose change of an IV infusion) and for holding the infusion and notifying the provider if the level is critically high.
What if? If the patient were being switched from IV heparin to oral warfarin, the nurse would expect to see orders for both aPTT and PT/INR, as there is an overlap period of several days where both drugs are administered concurrently until the INR reaches a therapeutic level.

How to Approach the Question

First, identify the key drug in the question: 'heparin sulphate'.
Next, recall the class of this drug: it is a potent anticoagulant.
Differentiate between the primary parenteral/IV anticoagulant (heparin) and the primary oral anticoagulant (warfarin).
Associate the correct laboratory monitoring test with each drug. A helpful mnemonic is 'WePT' (Warfarin is monitored by PT). By elimination, heparin is monitored by the other major clotting test, PTT.
Evaluate the options: 'Prothrombin time' is for warfarin. 'Hb level' is for bleeding, not drug effect. 'Clotting time' is outdated. This leaves 'Partial thromboplastin time' as the correct answer.

Concept Tested & Keywords

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Practise the full NORCET 5 Prelims - Sept 2023 (Shift-1)

Attempt every question from this paper in a timed mock, then review the full solution for each one.