Tutorial #26: DVT

Question 1

What is the modified Wells score for DVT (x10 items)

Answer 1

1. Paralysis/recent immobiization = 1
2. Active cancer or cancer treated within six months = 1
3. Recently bedridden for longer than 3 days or major surgery within the past four weeks = 1
4. Localized tenderness in the deep vein system = 1
5. Swelling of the entire leg = 1
6. Calf swelling > 3cm more than other leg =1
7. pitting edema greater confined to symptomatic leg = 1
8. collateral nonvaricose superficial veins = 1
9. previously documented DVT = 1
10. Alternative diagnosis more likely than DVT = -2

Question 2

In the 3-level Wells for DVT, what is the pretest probabily for “low probability of DVT” (-2 to 0). What is the best investigation to pursue at this time?

Answer 2

5%, can rule out with negative D-dimer

Question 3

In the 3-level Wells for DVT, what is the pretest probabily for “moderate probability of DVT” (1-2). What is the best investigation to pursue at this time?

Answer 3

17%, can rule out with negative D-dimer

Question 4

In the 3-level Wells for DVT, what is the pretest probabily for “high probability of DVT” (3-8). Can you use a D-dimer test?

Answer 4

53%, no role for D-dimer as rule out test

Question 5

List TWO patient populations where D-dimer is not used for rule out of DVT, and list why.

Answer 5

1. Inpatients: has been studied and shown that negative d-dimer with appropriate Wells Score DOES NOT rule out DVT.
2. Pregnant patients: this patient population that NOT been included in previous studies, and effectiveness of d-dimer is largely unknown*.

Notably, d-dimer PE CAN be used with YEARS criteria in pregnant patients, as shown in several trials. So far, no strong literature for rule out of DVT though.

Question 6

What is the diagnostic imaging choice for DVT?

Answer 6

ultrasound

Venography is considered the gold standard test for DVTs, however it is rarely, if ever, performed anymore.

Question 7

What is the usual treatment of DVT?

Answer 7

anti-coagulation

*Choices include heparin, LMWH, DOAC, wafarin.

*if it is the patients first VTE and it was precipitated by something, then theyre usually treated for 3-6 months AND until resolution of the precipitant. Otherwise patients are considered for indefinite treatment based on their individual risks for VTE which are weighed against their risk of bleeding.

Question 8

For a DVT, if ultrasound testing is negative, and the pre-test probability was low-moderate, what is the next best course of action?

Answer 8

DVT is ruled out

Question 9

For a DVT, if ultrasound testing is negative, and the pre-test probability was high, what is the next best course of action?

Answer 9

Repeating ultrasound in 1 week

Question 10

In clinical medicine, define the term “Miss rate”

Answer 10

The miss rate refers to the number of patients in whom we miss a particular diagnosis. In general, clinicians would like a low miss rate, but aiming for a zero miss rate leads to unnecesary testing.

Question 11

The risk factors for DVT include Virchows Triad, which is?

Answer 11

1. (venous) stasis
2. endothelial injury
3. hypercoagubility

1. Venous stasis -> recent immobilization/flight, casting, recent surgery or hospitalization.
2. Venous catheter placement, trauma
3. hypercoagubility -> malignancy, hormone replacement, IBD, pregnancy, family history of VTE.

Question 12

What are three positive predictors of DVT?

Answer 12

unilateral leg swelling, pain, and leg warmth.

Question 13

What is cellulitis? How can you differentiate on inspection from DVT?

Answer 13

it is a bacterial skin infection

Erythema, patch form and localized distribution.
- DVT does not localize in the same way as cellulitis

Question 14

What are the 3 positive predictors of cellulitis

Answer 14

1. Uniformly tender patch with associated erythema/warmth.
2. Fever
3. Pain/swelling distributed in contiguous area of soft tissue

Question 15

How can you differentiate chronic venous insufficiency from DVT?

Answer 15

Usually presents as bilateral and chronic swelling (*but chronic venous insuficiency can be unilateral as well)

Question 16

what are three positive predictors for chronic venous insufficiency?

Answer 16

1. bilateral swelling
2. skin discolouration
3. stasis ulcers

Question 17

In the 3-level Wells Score, what Wells point range corresponds to low probability of DVT, and how is DVT ruled out?

Answer 17

Score: –2 to 0

DVT is unlikely with a pre-test probability of ~5%

Can rule out with a negative D-dimer

Question 18

What test is the gold standard to diagnose DVT?

Answer 18

Venography is the gold standard but is rarely used today.

Ultrasound is the diagnostic test of choice.

Question 19

What is the diagnostic role of a single positive D-dimer in the evaluation of DVT?

Answer 19

A positive D-dimer is non-specific and cannot confirm DVT. It simply indicates that further imaging (e.g., ultrasound) is needed in the appropriate clinical context.

Question 20

What is a diagnostic cascade?

Answer 20

A diagnostic cascade is a sequence of follow-up tests or treatments that is triggered by an initial test result (often ordered without strong indication), which may lead to unnecessary interventions, costs, or harm.

Question 21

What is the difference between the testing threshold and the treatment threshold in clinical decision-making?

Answer 21

The testing threshold is the probability below which no further testing is needed because the disease is unlikely.

The treatment threshold is the probability above which treatment should begin without further testing.
Between these thresholds, testing is appropriate to guide management.