Antithrombin III levels should be measured when certain clinical findings are present.


Unexplained deep vein thrombosis or pulmonary embolus:

(1) personal history

(2) active disease

(3) family history


Presence of an underlying condition associated with acquired antithrombin III deficiency:

(1) DIC

(2) proteinuria

(3) cirrhosis


Possible resistance to heparin therapy:

(1) failure of aPTT or other monitoring test to prolong as expected for a given dosage regimen

(2) recurrent thrombotic event while on heparin


Situations increasing desirability of screening:

(1) preoperative

(2) possibly with oral contraceptive therapy


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