Evaluation of the Avoximeter: precision, long-term stability, linearity, and use without heparin

Abstract

Objectives. Because the AVOXimeter uses disposable cuvettes and makesits measurements directly in whole blood without first hemolyzing the sample,it does not need the care and maintenance that conventional co-oximetersrequire, it operates faster than conventional co-oximeters, and it is lessexpensive. Therefore, the objectives of this study were (1) to evaluate theprecision and linearity of the AVOXimeter’s measurements of totalhemoglobin concentration and oxyhemoglobin saturation; (2) to assess itslong-term stability and thus the required interval for re-calibration; (3) todetermine whether measurements can be made without anticoagulants; and (4) toassess the feasibility of storing blood samples in the disposable cuvettes.Methods. Measurements made by the test instrument were compared withthose of conventional co-oximeters or with standardized hemoglobin solutions.Blood samples were also collected with and without heparin to determinewhether anticoagulation is necessary. Results. Our tests confirmed thespecified precision of 0.3 g/dl for total hemoglobin and 0.5% foroxyhemoglobin. The results also showed that these measurements were linearwhen compared with a conventional co-oximeter, and they were consistent withthe specified accuracy of 0.45 g/dl for total hemoglobin and 1% foroxyhemoglobin. Weekly checks with control solutions showed that the instrumentholds its calibration for a year or more. Although treating syringes withheparin caused dilution errors, heparin did not affect the measurements whendilution was avoided. When blood samples were placed in disposable cuvettesand read repeatedly at 1-min intervals for 20 min, the readings driftedappreciably away from the original value. This drift occurred so slowly thatreadings taken at the first and second minute after the cuvette was filledwere within 1 or 2% of the original reading. Conclusions. In ourexperience, the test instrument was simple and easy to operate. It met thespecifications for precision and accuracy, its measurements were highlylinear, and it maintained a stable calibration for one year. If the cuvettesare filled as soon as blood is drawn, anticoagulation is unnecessary. However,the cuvettes should be read with 1 min of filling the cuvette.