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Five lactate dehydrogenase isoenzymes are normally observed in human serum: H4 (LDH1), H3M (LDH2), H2M2 (LDH3), HM3 (LDH4), and M4 (LDH5). This study presents evidence that these isoenzymes vary in the ratio of LDH activity (pyruvate → lactate) to LDH activity (lactate → pyruvate).

An Automatic Clinical Analyzer (DuPont ACA Prototype IV) was field evaluated. It is a discrete-sample, random-access analyzer which incorporates a new and unique method of performing chemical analyses. The analytical system is based on an expendable, clear plastic pack which serves as a reaction chamber and test cuvette. Serum specimens are introduced in plastic cups followed by plastic packs which are specific for each measurement. A report slip is generated which contains positive patient identification together with a list of measurements and results. Instrument performance was critically analyzed. Downtime was carefully noted. Erroneous results were detected by replicate analyses and comparisons with other methods. Acceptability by laboratory personnel was determined. The precision and accuracy of each method was analyzed, and normal ranges for young adults were determined. The Automatic Clinical Analyzer was found to be a reliable laboratory instrument with considerable potential for large and small volume workloads.

The reticulocyte count is a useful tool for evaluating anemia. However, its value depends on proper interpretation of the counting method used, taking into account any inherent error.

There is evidence that Q10 in the lactate to pyruvate spectrophotometric LDH assay may differ for heart and liver homogenates. The optimal lactate concentration for heart homogenate may increase from 0.4 to 0.6 M with change in temperature from 25° to 37°. Optimal lactate concentration for liver homogenate was 0.8 M at 25° and 0.6 M at 37°. These shifts in lactate optima with temperature are similar to those found by Vesell3. Differences in Q10 between LDH isoenzymes may make it difficult to compare LDH assays run at different temperatures on sera with different isoenzyme patterns. “Heart type” LDH would seem preferable for interlaboratory comparisons, since it conforms to the accepted Q10.

The method described is based on Dubowski’s o-toluidine procedure for the determination of glucose in plasma, serum, or cerebrospinal fluid. It utilizes the rapidity, precision, and closed system of continuous flow analysis of an unmodified AutoAnalyzer to substantially increase sensitivity and accuracy in the low range. The method is more specific than the ferricyanide reduction method. Protein precipitation or dialysis are unnecessary except for hemolyzed specimens and only 0.042 ml of sample are required. The method is inexpensive, easily performed, and compares favorably on a practical basis with enzymatic, reducing, and other aniline dye methods.

Quantitation of isoenzymes of lactate dehydrogenase by electrophoresis aids in diagnosis of diseases such as hepatitis and myocardial infarction. For accurate results, knowledge of isoenzyme distribution in various tissues and the half-life of each isoenzyme is important.

Free or unbound thyroxine (FT4) in serum comprises less than .1% of total circulating thyroxine. This small fraction is thought to be responsible for the physiologic action of thyroxine. Protein-bound iodine (PBI) butanol-extractable iodine (BE1) T4 by column and T4 by competitive protein binding are all measurements of total T4 in serum. They usually reflect thyroid status. However during pregnancy and with estrogen therapy total T4 is elevated and is not an accurate measure of thyroid disease as FT4 levels remain normal. This report describes a simplified rapid reproducible procedure for determining FT4 in serum. A 3.5-hour dialysis technic in which serum was diluted and labeled with T4-125 iodine was used. Subsequent purification of the dialysate was done with protein-coated charcoal. The shortened dialysis period eliminated the effects of bacterial contamination noted by longer methods. The protein-coated charcoal purification of the dialysate is less complicated than those previously described. Results compared favorably. Details of preparation of reagents and technics employed are given. Blood specimens were obtained from hyperthyroid and hypothyroid patients pregnant women women using oral contraceptives and euthyroid women sick with diseases not known to affect thryoid function. Diluted radioactive serum was prepared for each patient. Repeated freezing and thawing of serum samples with repetition of tests had no significant effect on results. Values between the various groups of patients agree with those found by other workers. Thyroid function in pregnant women and in women using oral contraceptives is shown by FT4 not total T4. The method described is suitable for routine use in clinical laboratories.

Twenty-four children with acute lymphocytic leukemia were compared with unmatched, unrelated normal controls for 20 HL-A specificities. No association between HL-A specificities and susceptibility to acute leukemia could be established. However, additional cytotoxic reactions were observed in the lymphocytes of three of six patients when malignant lymphoblasts were used as target cells. Since cytotoxic reactions occurred with multiple antisera detecting the same HL-A specificity, the data suggest the presence of neoantigens or the uncovering of existing antigens in leukemic lymphoblasts which cross react with the HL-A antigens normally present.

The glucose content in cerebrospinal fluid was determined on samples from 29 normal subjects. The determination was performed by both a copper reduction method and a hexokinase method, and results were compared with glucose values in serum from blood samples drawn simultaneously. The glucose values by the enzymatic method were 4.5% less than by the reduction method. The cerebrospinal fluid to serum glucose ratio was approximately 70% by either method, and although there appeared to be considerable correlation between levels of glucose in serum and cerebrospinal fluid, the serum level does not appear to be the sole determinant of cerebrospinal fluid glucose levels.

Oral contraceptive agents have many diverse and important extragenital effects, as manifested by alterations in laboratory test results. Drug therapy, as with oral contraceptive agents, is only one of many variables that must be considered in the knowledgeable interpretation and application of laboratory-generated data. (JAMA229:1762-1768, 1974)