Criteria

Wells score

  • Active cancer (treatment ongoing, within 6 months, or palliative): 1 point

  • Calf swelling where affected calf circumference measures >3 cm more than the asymptomatic calf (measured 10 cm below tibial tuberosity): 1 point

  • Collateral superficial veins (non-varicose): 1 point

  • Pitting oedema (confined to symptomatic leg): 1 point

  • Swelling of entire leg: 1 point

  • Localised pain along distribution of deep venous system: 1 point

  • Paralysis, paresis, or recent plaster immobilisation of lower extremities: 1 point

  • Recent bed rest for ≥3 days, or major surgery requiring regional or general anaesthetic within past 12 weeks: 1 point

  • Previous history of DVT or pulmonary embolism: 1 point

  • Alternative diagnosis at least as likely as DVT: subtract 2 points.

If the Wells score is ≥2, the patient is classified as ‘DVT likely' (absolute risk is approximately 40%).[85][86] If the Wells score is <2 the patient is classified as ‘DVT unlikely’ (probability <15%).[12][85][86]

[ Modified Wells score for deep vein thrombosis (DVT) Opens in new window ]

Ultrasonography criteria

The radiologist or technician who performs lower-extremity ultrasound first locates the femoral artery and vein in the groin region. The artery and its associated pulsatility can be identified readily; the femoral vein is adjacent. Inability to compress the vein indicates the presence of a clot, but provides no information on the age of the clot.[98]

All of the deep veins in the leg must be identified and compressed in a deliberate and systematic fashion (including the deep veins of the calf if whole-leg ultrasound is chosen). There must be a careful search for a duplicated femoral vein and a duplicated popliteal vein.

Secondary criteria include a larger vein diameter on the affected side, and absent or scant echoes within the clot. In acute DVT, the vein is non-compressible and dilated. In subacute DVT, the vein is non-compressible and marginally dilated or of normal size. In chronic DVT, the affected vein is non-compressible and small. Acute DVT is frequently easy to determine on the ultrasound, but where the vein is normal-sized or the vein is partially compressible or partially non-compressible, it is more difficult to determine the age of the DVT. In these cases, the DVT is referred to as age-indeterminant.

Warkentin Probability Scale for heparin-induced thrombocytopenia (HIT)[99]

The Warkentin Probability Scale for HIT (the '4T score') can be used to estimate the probability of a patient having HIT. [ Pretest Probability of Heparin Induced Thrombocytopenia (4-T's score) Opens in new window ] ​​ Points are scored (0, 1, or 2) for each of the 4 categories (maximum possible score = 8).

Thrombocytopenia

  • 2 points if >50% fall in platelet count to a platelet count nadir of ≥20 × 10⁹/L (≥20,000/mm³ or 20 × 10³/microL)

  • 1 point if 30% to 50% fall in platelet count, or if the nadir is 10-19 × 10⁹/L (10-19,000/mm³ or 10-19 × 10³/microL)

  • 0 points if <30% fall in the platelet count, or if the nadir is <10 × 10⁹/L (<10,000/mm³ or 10 × 10³/microL).

Timing* of onset of platelet fall (or other sequelae of HIT)

  • 2 points if onset is 5 to 10 days after starting heparin, or <1 day if there has been recent heparin (within past 30 days)

  • 1 point if onset is more than 10 days after starting heparin or if timing unclear; or if <day 1 after starting heparin with recent heparin (past 31-100 days)

  • 0 points if onset is within 4 days of first time heparin exposure (no recent heparin).

Thrombosis or other sequelae

  • 2 points if there is a proven new thrombosis, or skin necrosis, or acute systemic reaction after intravenous unfractionated heparin bolus

  • 1 point if there is progressive or recurrent thrombosis, or erythematous skin lesions, or suspected thrombosis (not proven)

  • 0 points if no thrombosis or other finding.

Other cause(s) of platelet fall

  • 2 points if none evident

  • 1 point if there is another possible cause

  • 0 points if there is another definite cause.

Pretest probability score

  • High = 6 to 8 points (probability of HIT approximately 50%)

  • Intermediate = 4 to 5 points (probability of HIT approximately 10%)

  • Low = 0 to 3 points (<1% probability of HIT).

*First day of immunising heparin exposure is considered day 0.

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