Accuracy of laboratory and portable monitor international normalized ratio determinations. Comparison with a criterion standard.

BACKGROUND: Portable instruments that measure the prothrombin time and automatically calculate the international normalized ratio (INR) with the use of a drop of whole blood have simplified the treatment of patients who are receiving warfarin therapy. The accuracy of these portable monitors has never been determined by comparing INR results with a criterion (gold) standard INR determination. METHODS: Duplicate whole-blood INR determinations were made with two commercially available portable INR monitors. Duplicate frozen-plasma samples were measured with four different thromboplastin reagents, each with a different international sensitivity index. The criterion standard INR was determined by using an international reference thromboplastin and the manual tilt-tube technique. Agreement was evaluated by determining how accurately laboratory and monitor INR determinations matched criterion standard values in designating a sample to be within or outside of currently recommended INR target ranges. RESULTS: Two of the laboratory methods, which used relatively sensitive thromboplastins, showed close agreement with the criterion standard, whereas two laboratory methods that used less sensitive thromboplastin reagents showed poor agreement. Both of the portable monitors fell between these extremes. The two best laboratory methods ere significantly better (P < .003) than both monitors, which in turn were better (P < .003) than the remaining two laboratories. CONCLUSIONS: There is large interlaboratory variation in the accuracy of INR determinations. Laboratory methods that used insensitive (high international sensitivity index) thromboplastins performed poorly. Accuracy of monitor measurements appears satisfactory.

Hypoglycemia after administration of somatostatin analog (SMS 201-995) in metastatic carcinoid.

SMS 201-995 (Sandoz Pharmaceuticals, East Hanover, NJ) is a synthetic peptide analog of native somatostatin that has been used to relieve symptoms caused by neuroendocrine tumors. Reports have described an insulin suppressive effect of SMS 201-995 that results in elevations of blood glucose. We report a patient with a metastatic small bowel carcinoid and renal failure in whom mild symptomatic hypoglycemia occurred 30 to 60 minutes after SMS 201-995 administration. No increase in insulin or decreases in glucagon, cortisol, or catecholamines were observed during these hypoglycemic episodes. Elevated levels of growth hormone fell gradually following SMS 201-995 administration and did not temporally correspond to the 30- to 60-minute nadir of blood glucose. However, SMS 201-995 levels peaked during this 30- to 60-minute period. As clinical experience with this drug broadens, patients whose glucose control is dependent on counter-regulatory hormones should be monitored for the possibility of hypoglycemia.