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Objectives: The naming convention in coagulation may cause confusion in electronic ordering systems, leading to inappropriate test orders. We implemented test utilization efforts and studied utilization before and after interventions for two specialty coagulation assays., Methods: Two interventions were implemented: test names were changed from factor assay to activity, and residents reviewed all factor V and X requests. A retrospective review of factor V and X activity orders was performed for the period 1 year before and after interventions., Results: After interventions, factor V and X activity orders decreased by approximately 40%. Resulted tests decreased by 53.8% and 47.8%, corresponding to reductions of $2,493.05 and $1,867.80 per year in laboratory charges for factor V and factor X activity, respectively. Abnormal factor V activity results increased from 45% to 59%. Factor V activity orders from outpatient clinics decreased by 21.6%., Conclusions: Simple interventions can reduce inappropriate specialty coagulation test orders and unnecessary costs., (© American Society for Clinical Pathology, 2019. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

A 67-year-old woman had symptoms of an upper respiratory tract infection for which she received a five-day course of erythromycin. Epistaxis and gross hematuria subsequently developed, and the patient was found to have a selective Factor X deficiency. She received supportive therapy and prothrombin complex concentrates (Factors II, VII, IX, and X), with subsequent resolution of her transient Factor X deficiency. Her hospital course, however, was complicated by the development of multiple cerebral infarctions. This is the tenth reported case of transient Factor X deficiency not associated with amyloidosis. In seven of the previous cases, as in this patient, the deficiency was associated with a preceding upper respiratory infection. This is the only case, however, with evidence of inhibitory activity in the plasma that was directed toward Factor X.

Factor X was assayed using chromogenic substrate S-2222 for four patients with severe factor X deficiency and for nine patients with homozygous or heterozygous factor X Friuli disorder. Factor X Friuli disorder is characterized by the presence of an abnormal factor X that is normally activated by Russell's viper venom, but is not activated by tissue thromboplastins. The levels of factor X found in factor X deficiency varied between 2 and 10% of normal and therefore were higher than those found in the same plasmas using "clotting" methods (1% or less than 1% of normal). The levels of factor X found in homozygous factor X Friuli patients varied between 4 and 11% of normal, and therefore were practically identical to those found by means of clotting methods that employed tissue thromboplastins (7-9% of normal). These values were definitely lower than those obtained using a Russell's viper venom and cephalin mixture as thromboplastin (82-92%). A similar pattern was observed for patients heterozygous for the abnormality. These findings indicate that "amidolytic" methods are not necessarily identical to clotting methods. Furthermore, they indicate that substrate S-2222 is not specific for factor X.

Specific radioimmunoassays, sensitive to plasma levels of less than 1% of normal, were developed for protein C and Factor X. In 31 normal subjects, mean plasma antigen levels were as follows: protein C, 3.23 +/- 0.79 microgram/mL (2 SD); Factor X, 7.74 +/- 1.81 microgram/mL. In patient son chronic warfarin therapy, protein C and factor X were depressed equivalently: protein C, 42% +/- 20% (of a pooled plasma reference); Factor X, 44% +/- 24%. Protein C antigen fell much more rapidly than Factor X antigen when warfarin therapy was begun, creating an initial period of potential hypercoagulability. In patients with severe liver disease, mean protein C antigen (25% +/- 17%) was lower than Factor X antigen (51% +/- 29%). Protein C antigen levels did not appear to be a sensitive indicator of compensated intravascular coagulation or systemic fibrinolysis induced by infusion of streptokinase. Clinical implications of these findings are discussed.

The relative sensitivities of the prothrombin time, Russell's viper venom time and activated partial thromboplastin time were determined in one-stage quantitative assays for factor V and factor X. Sensitivity was defined as the slope of the reference curve. The prothrombin time was the most sensitive test for factor X and the least sensitive for factor V. The Russell's viper venom time was the most sensitive test for factor V and least sensitive for factor X. The activated partial thromboplastin time approximated the sensitivity of Russell's viper venom for factor V and had intermediate sensitivity for factor X. The data indicate that factor V is best quantitated by the Russell's viper venom time and factor X by the prothrombin time, exactly the opposite of what is customarily done.