Don’t test vitamin K levels unless the patient has an abnormal international normalized ratio and does not respond to vitamin K therapy.
|Rationale and Comments:||Measurements of the level of vitamin K in the blood are rarely used to determine if a deficiency exists. Vitamin K deficiency is very rare, but when it does occur, a prolonged prothrombin time and elevated international normalized ratio will result. A diagnosis is typically made by observing the prothrombin time correction following administration of vitamin K, plus the presence of clinical risk factors for vitamin K deficiency.|
|References:||• Suttie JW. Vitamin K. In: Machlin L, ed. Handbook of Vitamins. New York, NY: Marcel Dekker; 1984:147.
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