Specimen collection in plastic containers gives rise to interferents in liquid-chromatographic assay of cyclosporine.

CK-MB values of >9 U/L and >4% CK-MB for potential MI. Because the modified calibration causes an “apparent” loss of CK-MB at the low end when compared with the KOdak calibration, we needed to determine whether the modified procedure retained good sensitivity. We analyzed a series of samples from two patients who displayed clinical evidence of MI 24 to 48 h before admission. The Hybritech procedure failed to detect any significant CK-MB in any specimen, <2.0 and 2.6 pg/L from each patient; however, the modified Ektachem 700 CK-MB procedure clearly showed a significant CK-MB and %CK-MB for both patients: the CK ranges were 169-144 and 369-221 UIL and CK-MB ranges were 13-7 and 16-3 U/L for the two. This was confirmed by the Roche Isomune assay for LD1 (42% and 61%), which was also positive for suspected MI beforeadmission (normal <34% ± 2%). In addition we compared results of our Ektachem procedures for total CK and for %CK-MB with those of the chemistry laboratory of a nearby community hospital that uses electrophoresis to estimate %CK-MB. Thirty-two specimens from 14 of 15 cardiac patients, all considered positive by the criteria of the community hospital, were clearly positive by our modified criteria; one was considered borderline. A statistical comparison of our data (y) with theirs (x) by linear regression (y = hr + a) gave the following results: for total CK, the slope (b) and intercept (a) were 2.21 and -13.7, respectively. The unexplained error [square root of s2I(n 2)] was 0.055. The product moment correlation coefficient (r) was 0.991. For CK-MB, the slope and intercept were respectively 0.614 and 0.26. Unexplained error was 0.088; the r value was 0.787. Because the CK-MB assay currently can be performed in the Ektachem 700 for less than $1.00 per test for reagents, in less than 10 mm, and is not susceptible to variations in technique, we thought that this procedure would be of considerable benefit to total patient care. However, the original Kodak calibration and set of criteria to evaluate CK-MB and %CK-MB results forsuspected MI can lead to confusing interpretations. Modi1ring the calibration and using simpler criteria for evaluating results appears to be possible without loss of sensitivity or specificity.