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The authors evaluated the Kodak Ektachem Slides for total, "direct," conjugated, unconjugated, and albumin-bound ("delta") bilirubin. For various concentrations of control material, the precision (CV) within- and between-day ranged from 1.7 to 2.4% (2.8-6.6%) for total bilirubin, 0.8-4.2% (1.6-11.5%) for unconjugated bilirubin, and 1.6-9.5% (2.6-20.7%) for conjugated bilirubin. The Ektachem total and "direct" bilirubin assays demonstrated excellent correlation with the Jendrassik and Grof procedure; a 30% difference was observed, however, between absolute numbers with the two direct bilirubin methods. We found the measurement of true conjugated bilirubin by the Kodak Method to be superior to the measurement of "direct" bilirubin in following the response to treatment of various hepatic disorders manifested by extrahepatic and intrahepatic biliary obstruction.

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We evaluated the Kodak Ektachem multilayer ammonia and creatinine slides. For various concentrations of control material the precision (CV) within- and (between-day) ranged from 0.8 to 7.8% (4.4-9.0%) for ammonia, and 1.9-25.1% (3.6-13.9%) for creatinine. A number of commercial control fluids were unacceptable choices due to the presence of elevated endogenous ammonia levels. For both analytes, analytical recovery was in the range of 100 to 108%. Comparison with the Jaffe reaction demonstrated good correlation for creatinine, and linearity was judged acceptable for both analytes. For ammonia, serum values were nearly double those of paired plasma samples. Plasma and serum samples, therefore, cannot be used interchangeably. No serum versus plasma differences were observed for creatinine.

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We evaluated the Kodak Ektachem multilayer ion-selective electrolyte slides. For various types and concentrations of control material the precision (CV) within- and between-day ranged from 0.5 to 1.3% (1.7-2.1%) for sodium, 1.2 to 2.2% (2.7-2.9%) for potassium, 2.9 to 4.6% (5.9-6.7%) for carbon dioxide, and 0.7 to 1.6% (1.3-1.4%) for chloride. For all these analytes, analytical recovery was about 100%, except in the supra-physiological ranges, for which carbon dioxide recovery was about 110-120%. Either serum or heparin-treated plasma can be used, interchangeably, for analysis; use of serum treated with lithium iodoacetate is unacceptable. Comparisons with results by continuous-flow procedures demonstrated good correlation for sodium, potassium, and chloride; carbon dioxide comparisons indicate an Ektachem calibrator change may be required. Abnormally low protein concentrations or lipemia had no observed effects on results for electrolytes. Abnormally high protein concentrations affect sodium results slightly (approximately 5 mmol/L).

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We determined appropriate temperatures for sample storage and the resulting stability of 14 analytes commonly radioimmunoassayed in the clinical laboratory. Serum specimens to be tested for concentrations of cholylglycine, cortisol, digoxin, ferritin, follitropin, immunoglobulin E, lutropin, prolactin, thyroxin (also blood-spot thyroxin), triiodothyronine, and triiodothyronine uptake could be stored for up to two weeks at room temperature, refrigerated, or frozen without any loss of analyte activity. Specimens for insulin testing require freezing or refrigeration, and specimens for gastrin testing should be stored at -70 degrees C for optimal results.

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Recent evidence (Kolhouse et al., N. Engl. J. Med. 299: 785-792, 1978) demonstrates that commercial cobalamin (Vitamin B12) radioassay kits contain nonspecific R-protein binding agents that can give falsely normal results in patients who are actually cobalamin deficient. We tested three kits: with "purified" intrinsic factor as the binder, with intrinsic factor and the nonspecific R-protein sites blocked with "cobinamide," and non-purified intrinsic factor-R-protein binder. Results with use of the first two compared well with those by a microbiological assay (Lactobacillus leichmannii) and are in harmony with clinical impressions.

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Some basic laboratory performance criteria were studied for the Eastman Kodak glucose and urea nitrogen analyzer. Serum, plasma, urine, and cerebrospinal fluid were tested. Precision, both "within-day" and "between-day," for both analytes was less than 2.2% (CV). Both analytes demonstrated linearity, with about 100% recovery of added substrates. Comparisons with continuous-flow procedures demonstrated good correlation. A variety of sera and plasmas can be used for glucose analysis; oxalate--fluoride-treated plasma is unacceptable for use in analysis for urea nitrogen. We saw no effects on glucose or urea nitrogen analysis from hemolysis, lipemia, icterus, some common drugs, ammonia, or abnormally high protein concentrations. Minimum amounts detectable were: glucose (serum) 104 mg/L; glucose (cerebrospinal fluid) 100 mg/L; and urea nitrogen (serum) 21 mg/L. Calibration procedures are discussed for protein-based and aqueous samples.

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We have evaluated a new non-chromatographic commercial radioimmunoassay kit for serum, plasma, and urine aldosterone levels which employs 125 iodine as the tracer. Within-run and run-to-run precision data show coefficients of variation of 3 to 6% and 8 to 16%, respectively. Recovery of aldosterone added to serum and urine at several levels range from 92 to 109%. Antibody specificity was tested with six structurally related steroids at grossly elevated concentrations and no crossreactivity was observed. Serum or plasma can be used interchangeably in the assay, and normal levels correspond to generally accepted values.

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We evaluated results for serum vs. plasma for 12 selected radioassay procedures. Blood samples were collected with heparin, oxalate-fluoride, or ethylenediaminetetraacetate as anticoagulant and compared with the corresponding serum samples. In combination with a previous report [Kubasik, N.P., and Sine, H.E., Clin. Chem. 24 137 (1978)] we have now tested a total of 25 different analytes, using 31 manufacturers' kits. Differences were again demonstrated between serum and plasma that may be of sufficient magnitude to alter clinical interpretation of the results. Assays also demonstrated differences based on the procedure used.

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We evaluated a modified procedure for a commercially available myoglobin radioimmunoassay kit (Nuclear Medical Systems). Within-run and run-to-run precision was acceptable. Normal ranges were established and paralelism studies performed. Clinical usefulness was assessed in 100 consecutive patients admitted to our coronary-care facility. The determinations were done daily, along with creatine kinase and its isoenzymes, and lactate dehydrogenase and its isoenzymes. Fifty of the 100 patients ultimately were shown to have had acute myocardial infarction. Myoglobinemia was present in most of the patients with acute myocardial infarction, but information on its presence was less usefull clinically than was detection of creatine kinase isoenzyme MB.

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CPK MB isoenzymes were qualitatively identified using an electrophoresis method in 166 patients with acute cardiovascular disease during a six month period. Forty-three had total CPK activity in the normal or borderline range (0--75 U/Liter at the time the MB isoenzyme was first identified. Fifteen of these patients were diagnosed as having had a new acute myocardinal infarction (Group I) and another 15 as having had an old myocardial infarction (Group II). Diagnosis was based on electrocardiographic changes or autopsy findings. The remaining 13 patients were classified as "ischemic heart disease" (Group III) in the absence of strict electrocardiographic criteria or autopsy evidence of myocardial infarction. Nine of the 15 patients in Group I subsequently had elevations of their total CPK activity above 75 U/L. In contrast the total CPK activity of only one patient from Group II and Group III subsequently exceeded 75 U/liter. All 43 patients had evidence of cardiovascular disease. Our findings suggest that the detection of MB isoenzyme in the presence of a normal total CPK activity is a significant laboratory finding and is indicative of cardiac myofiber injury.

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We evaluated the results for serum vs. plasma samples for 15 selected radioassay procedures, using 19 manufacturers' kits. Blood samples were collected with heparin, oxalate-fluoride, or ethylenediaminetetraacetate anticoagulants and compared with serum samples. Differences were demonstrated between serum and plasma which may be of sufficient magnitude to alter clinical interpretation of the results. Assays also demonstrated significant differences based on the kit manufacturer and procedure used.

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