Assessment of a diagnostic dip-stick for assaying plasma or serum pseudocholinesterase activity

A diagnostic dip-stick for measuring pseudocholinesterase activity has been assessed by 4 participants and compared with a standard spectrophotometric method. Duplicate dip-stick estimations (measured in kU/l) corresponded closely, and concurrence between participants was good. The dip-stick estimate of cholinesterase was consistently lower than the spectrophotometric value; the magnitude of this deviation depended on the absolute enzyme activity. With enzyme activities of up to 1 kU/l the dip-stick value was 1 unit lower. Between 1 and 4 kU/l the dip-stick estimate compared well with the spectrophotometric value. From 5 to 7 kU/l and beyond 7 kU/l the negative deviation recorded by the dip-stick increased to 2 units or more. Normal enzyme activity is 3 - 6 kU/l. Over the 1 - 4 kU/l range the method is most accurate, thus negative deviation below 1 kU/l or above 4 kU/l is generally diagnostically irrelevant. On the basis of cost, convenience, speed and accuracy this method will suffice in the absence of sophisticated assay facilities.