Beckman. ICS anti-IgG, anti-IgA, and anti-IgM. (Beckman,. Inc., Brea, CA) .... J. Hinds,2 and Jack. H. Ladenson'. (' Div. of Lab. Med., Depts. of Pathol. and. Med.
of methemalbumin.
5. Bertrand
Clin
Chem
1975;21:1506-10.
A, Cox C, Foucart
methemalbumin 1982;123:121-6.
by second-derivative
P, et al. Determination of serum spectroscopy. Clin Chini Acts
methods in which CK-M is precipitated will yieM ?aisey high results for CK-MB, owing to interference by CK-BB. Immunoprecipitation and subsequent electrophoresis cannot be used to quantify CK-MB unless it is shown that all macro-CK is quantitatively removed. This method certainly can be used for detection of an interference, however. References
Macro-Creatlne Electrophoresis,
Kinase
Co-Migrating
with CK-MB
on
(Pathol. Dept., Med. Coll. of Virginia, P.O. Box 597, Richmond, VA 232980597; present address: Dept. of Labs., Sparrow Hosp., 1215 E. Michigan Ave., Lansing, MI 48909) Dennis
W. Jay
Certain types ofmacro-CK, type 1, have been reported to cause false increases in CK-MB by co-migration on electrophoresis (1-3). I report two such cases in which the macroCK was an IgA with anti-CK-BB specificity. According to methods proposed by Medeiros et al. (1), immunoprecipitation and subsequent analysis by elecrophoresis was used to separate interfering macre-CK from CK-MB. CK electrophoresis (Corning, Palo Alto, CA), after incubation of serum with Beckman ICS anti-IgG, anti-IgA, and anti-IgM (Beckman, Inc., Brea, CA), revealed a marked diminution ofapparent CK-MB activity only with anti-IgA. Incubation of serum with anti-CK-BB and anti-CK-MM (Cambridge Medical Diagnostics, Billerica, MA) and subsequent electrophoresis demonstrated a marked decrease in the apparent CK-MB fraction only with anti-CK-BB. No detectable CK-MB was found with the Tandem-E CK-MB assay (Hybritech, Inc., San Diego, CA). I corroborate the results of others and conclude that certain type 1 macro-CK species may cause a falsely increased CK-MB as determined by electrophoresis. However, it has been previously suggested that a proportion of apparent CK-MB activity >40% should alert one to the presence of this interference (1). Samples from these cases contained lower percentages, demonstrating the uncertainty of this criterion in predicting this interference. Expressed in absolute units, apparent CK-MB remained stable over an extended period of time, demonstrating the interference more clearly (Table 1). One further aid in suspecting macro-CK interference with CK-MB on electrophoresis may be the presence of a second macro-CK appearing between CK-MM and CK-MB or as a shoulder on the CK-MM peak. Both of these cases had patterns of this nature, as did at least three other reported cases (2, 3). At present, the only clinically available assays specific enough for quantifying CK-MB in these patients are the Tandem-E CK-MB (Hybritech) or the QuiCK-MB (International Immunoassay Laboratories). Immunoinhibition
Table
1. CK Electrophoresis CK, U/L
MB, U/L
11/27 11/28
339
54
267
64
11/29
192
60
12/05
130 135 113
58 69 67
Date
Patient CW
12/06 12/11 Patient
HJ
02/06
109
29
02/07
92
34
02/08
112
34
1920
CLINICAL CHEMISTRY,
Vol. 34, No. 9, 1988
1. Medeiros U, Greco FA, Walsh D, Gerson B. Macro creatine kinase type 1 with electrophoretic mobility identical to that of th MB iaoenzyme. Clin Chem 1985;31:1393-6. 2. Jockers-Wrethu E, Fleming E. Atypical serum creatine kin isoenzyme pattern caused by complexing of creatine kinase-B with immtmoglobulins G and A. J Clin Chem Clin Bioche 1979;17:731-7. 3. Greco FA. Identifying CK-MB and macro-CK by electrophores [Letter]. Clin Chem 1987;33:1954-5.
Microtransferrlnurla Early Glomerular Mlcroalbuminurla,
Is a More Sensitive Indicator Damage In Diabetes than
of
A. M. Bernard, A. A. Ouled Amor, J. J. L. Antoine, R. R. Lauwerys, A. Lambert, and B. Vandeleene (Units of Industrial Toxicol. and of Diabetol. & Nutrition, School of Med., Univ. of Louvain, B-1200 Brussels, Belgium) Goemaere-Vanneste,
Microalbuminuria (or “pauci-albumunuria,” see Clin Chem 1988;34:209-10), defined as abnormally increased urinary excretion of albumin in the absence of clinical proteinuria, is now widely used as a predictor of diabetic nephropathy (1). We have evidence that determination ofurinary transferrim is more sensitive than determination of albumin for early detection ofglomerular involvement in diabetics. The urinary excretion of both proteins was determined by latex immunoassay (2) in 176 diabetics: 84 with type I, 23 with type II, and 69 with type ifi diabetes (mean age and duration of disease, 52 and 14 y, respectively). Prevalences of increased values were calculated by using as upper limit of normal 23.4 mg/g creatinine (Cr) for albumin and 0.70 mg/g Cr for transferrin (geometric mean + 2 geometric SD ofvalues found in an age-matched control group of 57 subjects). Seventy-eight diabetics showed an increased urinary excretion of both proteins; 23 were positive for transferrin alone, but only seven for albumin alone (marginal x2: 8.5, P
