When increasing amounts of purified antithrombin III are added to a known amount of thrombin, the enzymztic activity of the thrombin decreases.
Since antithrombin III binds irreversibly to thrombin, the decrease in thrombin activity is proportional to the amount of antithrombin III that is added to the assay.

Normal plasma inhibits thrombin

When a small amount of a patient's plasma is added to thrombin, the antithrombin III that is present in the plasma decreases the thrombin activity.

Question

From the above results you can conclude that:

James has twice the normal amount of antithrombin III
James has half the normal amount of antithrombin III protein
James has half the normal amount of antithrombin III activity
James has either too much heparin, too much thrombin or too little antithrombin III

Question

When determining the antithrombin III activity, the laboratory added a low molecular weight form of heparin to the solution. Why was the heparin analogue added?

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James' Unwanted Blood Clots

Antithrombin III inhibits thrombin

Normal plasma inhibits thrombin

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