During morning rounds, a patient who underwent right total knee arthroplasty 6 days ago is… — USMLE Step 2 CK

During morning rounds, a patient who underwent right total knee arthroplasty $6$ days ago is evaluated for new-onset left leg pain and swelling. The patient, a female in her mid-sixties, has been receiving standard postoperative venous thromboembolism prophylaxis with subcutaneous unfractionated heparin since the day of surgery.

Vital signs are:
Temperature: $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ )
Heart rate: $92\text{/min}$
Blood pressure: $128/82\text{ mm Hg}$
Respiratory rate: $14\text{/min}$
Oxygen saturation: $97\%$ on room air

Physical examination reveals a swollen, erythematous, and tender left calf. The right surgical site is healing appropriately without signs of infection or excessive bleeding.

Laboratory studies are as follows:

Admission (Day 0):
Hemoglobin: $13.5\text{ g/dL}$
Platelet count: $280,000/\mu\text{L}$

Today (Day 6):
Hemoglobin: $12.8\text{ g/dL}$
Platelet count: $118,000/\mu\text{L}$
Leukocyte count: $7,200/\mu\text{L}$

Based on these findings, which of the following is the most appropriate next step in management?

Immediate cessation of unfractionated heparin and initiation of argatrobanCevap
B
Discontinuation of unfractionated heparin and initiation of enoxaparin
C
Continuation of the current regimen and immediate duplex ultrasonography of the left lower extremity
D
Discontinuation of unfractionated heparin and initiation of warfarin monotherapy
E
Transfusion of one unit of apheresis platelets and discontinuation of heparin

Cevap

Immediate cessation of unfractionated heparin and initiation of argatroban

This patient's clinical presentation—a platelet count drop of greater than

50\%

occurring

6

days after starting unfractionated heparin, coupled with a new thrombotic event (deep venous thrombosis)—strongly suggests Heparin-Induced Thrombocytopenia (HIT). HIT is an immune-mediated prothrombotic disorder caused by IgG antibodies against heparin-platelet factor 4 (PF4) complexes. The diagnosis is strongly suspected clinically based on the 4T score (Thrombocytopenia, Timing of platelet fall, Thrombosis, and absence of oTher causes). The single most critical initial step in suspected HIT is to immediately discontinue all heparin-containing products (including heparin flushes) and initiate anticoagulation with a non-heparin agent. A direct thrombin inhibitor (such as argatroban or bivalirudin) or fondaparinux must be started to manage the extreme prothrombotic state. Waiting for laboratory confirmation (such as a PF4 ELISA or serotonin release assay) before changing therapy is inappropriate, as the patient remains at an immediate high risk for life-threatening thrombotic events.

Adım Adım Çözüm

Evaluate the laboratory values for significant changes.

The platelet count has dropped from

280,000/\mu\text{L}

118,000/\mu\text{L}

(a drop of

>50\%

), occurring precisely

6

days after the initiation of unfractionated heparin.

Recognizing a significant relative drop in platelets (even if the absolute number is not severely low) during the typical

5

10

day window is the key to identifying Heparin-Induced Thrombocytopenia (HIT).

Identify clinical signs of complications related to the platelet drop.

The patient has developed a new swollen and erythematous calf, highly indicative of a new deep venous thrombosis (DVT).

Thrombosis, not bleeding, is the hallmark complication of the prothrombotic state caused by HIT antibodies activating platelets.

Determine the definitive immediate management step.

Stop all heparin products immediately and start a direct thrombin inhibitor (e.g., argatroban).

Given the high probability of HIT based on the 4T score (timing, platelet drop, and new thrombosis), empirical treatment must begin immediately to prevent catastrophic thrombotic events like pulmonary embolism or limb gangrene.

Anahtar Kavram

Management of Heparin-Induced Thrombocytopenia (HIT)

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

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