Raymond E. Vanderlinde

Proficiency testing in acid-base analyses: An interlaboratory evaluation

Estimation of pH, PCO2 and total CO2 in serum-based samples by laboratories in New York State was evaluated. Participant laboratories (122) showed average coefficients of variation of 8.8% for pH, 13.3% for PCO2 and 15.0% for total CO2 measurements. Coefficient of variation for measurement of pH in aqueous buffers was < 4%. A slightly improved performance in the estimation of PCO2 was noted for laboratories using quality control sera. Participant data, grouped by manufacturer of equipment used, revealed neither mean values nor standard deviations substantially different from overall performance. A direct correlation is shown between weekly workload and laboratory performance in this area of chemical testing.

Linearity and accuracy of ultraviolet and visible wavelength photometers: An interlaboratory survey

A survey was made to determine the linearity and accuracy of ultraviolet and visible wavelength photometers used by laboratories in New York State. Two solutions each of high-purity potassium dichromate and cobalt ammonium sulfate were submitted for photometric performance studies. The majority of the participant spectrophotometer results showed good correlation with reference data. Broad half-band width (greater than 10 nm) photometers showed little deviation from linearity. Coefficients of variation for the models surveyed were 5-10%.

The effect of temperature on the kinetic constants of human lactate dehydrogenase 1 and 5.

The kinetic constants of human lactate dehydrogenase 1 and 5 (L-lactate: NAD+ oxidoreductase, EC 1.1.1.27), assayed lactate-to-pyruvate increase with temperature. The reaction mechanism is ordered sequential as has been found with lactate dehydrogenase from other sources. The KM values for each substrate are larger for isoenzyme 5 than for 1. For lactate dehydrogenase 1 the KM(lactate) increases from 1.07 mM at 25 degrees C to 3.95 mM at 37 degrees C and for lactate dehydrogenase 5 it increases from 5.37 mM at 25 degrees C to 6.88 mM at 37 degrees C. The KM(NAD+) for lactate dehydrogenase 5 is 0.14 mM at 25 degrees C and 0.29 mM at 37 degrees C. The increase in the KM for each substrate with increasing temperature confirms that additional substrate is required for optimal reaction conditions at higher temperatures.

The lack of L-thyroxine inhibition of human aspartate aminotransferases

1. L-Thyroxine, which inhibits several transaminases, was shown to have no such effect on human aspartate aminotransferases (AspAT). 2. No inhibitory effect was observed at optimal or suboptimal aspartate concentrations with the enzyme in human serum or isoenzymes purified from human tissues. 3. Thyroxine was also shown not to interfere with the stimulation of AspAT by pyridoxal phosphate. Human cytoplasmic and mitochondrial AspAT differ from some other pyridoxal-requiring enzymes in showing this lack of thyroxine inhibition.

The clinical biochemistry of phosphorus

Summary 1. Considerable evidence indicates that the long term use of antacids may result in a “phosphorus depletion syndrome”. Furthermore, the widespread treatment of peptic ulcer with non-absorbable antacids makes recognition of this syndrome clinically important. 2. “Mountain sickness” may result when a marked rise in 2,3-diphosphoglycerate acid (2,3-DPG) fails to take place within the red cells; this rise normally facilitates oxygen release at physiological tensions. The 2,3-DPG level is likely to be depressed in uremia when hypophosphatemic patients are treated with aluminum hydroxide gel. 3. ACD (acid-citrate-dextrose) stored blood becomes severely depleted of 2,3-DPG in less than two weeks and massive blood transfusions with 2,3-DPG depleted blood may be hazardous. CPD (citrate-phosphate-dextrose) solutions affect the organic phosphates such as adenosine and aid in maintaining the 2,3-DPG level of stored cells. 4. The chemical methods for the determination of phosphorus have been reviewed including blood collection procedures, preparation of protein-free filtrates, the automated method utilizing dialysis, and the newer direct phosphorus procedures. 5. Current methodology in use in the clinical laboratories of New York State has been evaluated.