Technique and Practical Problems: Comparative Studies of the Value of Two Cyanide-Xitroprusside Methods ix the Diagnosis of Cystixuria: Cystinuria in Sweden,Part ix

We have tested a Quantitative Buffy Coat (QBC) instrument (Becton Dickinson, USA), and compared results obtained with this instrument to results obtained with standard methods in a haematology clinic.

The basic principle of the method is a classical haematocrit centrifuge. The analysis provides a haematocrit value, platelet count, a total white blood count, and separates the white blood cells in granulocytes and mononuclear cells (lymphocytes plus monocytes).

The instrument is easy to use but requires a trained observer. All results are available in 15 min. We have found the accuracy of the method good for all parameters. The precision of the instrument is good but for estimation of granulocytes and lymphocytes plus monocytes we did not find the high sensitivity claimed by the manufacturer (manufacturer's lower limit 0.02x 10⁹/1; standard deviation for low levels of granulocytes: 0.300×10⁹71 and lymphocytes plus monocytes: 0.235×10⁹/1).

A large fraction of samples (leukocytes 27%, platelets 40%) from a haematological clinic falls beyond the limits for reliable results set by the manufacturer, which reduces the utility of the instrument in such patients. Furthermore, in 21% and 10% of samples within the recommended range for leukocytes and platelets, respectively, QBC results could not be read owing to ill-defined boundaries. For granulocytes and lymphocytes plus monocytes 25% and 34% of the samples, respectively, could not be read owing to ill-defined boundaries. The instrument is not constructed to protect against blood contamination of the centrifuge and, therefore, the safety of the instrument is not satisfactory.