Letter: Interbatch variability in measurement of urinary amylase with a commercial kit.

buffer (50 mmol/liter Tris-HC1, pH 7.5, containing 300 mmol of NaCl per liter). The BB values are significantly different in samples 1, 3, and 8, where the true MB activity is >40 U/liter. The remaining samples with <40 U of MB per liter do not show any significant carryover of MB to BB. We are in the process of changing the MB buffer-salt content; this will essentially eliminate the MB to BB carryover at high MB values. Mercer implies that a system designed to separate CK isoenzymes by gradient elution on macro-columns will not work on micro-columns with a discontinuous gradient. Yasmineh and Hanson (8), however, showed excellent correlation between gradient elution on macro-columns and discontinuous elution on micro-columns. To date, comparison of isoenzyme data obtained by Worthington’s procedure and that of Yasmineh and Hanson has been limited. Table 6 shows four representative samples of our initial data; the values are quite comparable. We feel our isoenzyme procedure is the best available and has a performance in numerous laboratories far superior to that found by Mercer.