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J Appl Physiol 102: 2416, 2007; doi:10.1152/japplphysiol.00108.2007
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LETTER TO THE EDITOR

Comments on "Experimental determination of net protein charge, [A]tot, and Ka of nonvolatile buffers in bird plasma"

TO THE EDITOR: I am writing to express some concerns about the article by Stämpfli et al. (7), "Experimental determination of net protein charge, [A]tot, and Ka of nonvolatile buffers in bird plasma."

First, it appears that the BCG dye binding technique was used to determine albumin concentration. This technique has not been validated for avian albumin and does not correlate with electrophoretic results (4). Electrophoretic determination of albumin concentration would have been a better choice of measurement. I think the authors need to qualify their statements about indexing [A]tot to albumin concentration, as their measurements may have been in error.

Second, the authors use an incorrect term, "total solids," to describe the readings obtained from a Leica Vet 360 refractometer. They were actually measuring total protein by a total solids technique. The term total solids refers to all solutes in plasma and is ~15–20 g/l higher than the protein concentration for most mammalian samples. Refractometers measure protein by the angle of light produced by refraction caused by the total solids in the sample and then subtracting the expected amount of refraction from non-protein solids in the sample. The Leica Vet 360 includes that calculation and has protein (g/dl) listed clearly on the scales in the internal reticle (2).

Refractometers have been reported to give higher results than the biuret technique for avian samples for various species of birds (4–6). That discrepancy may be due to relatively higher glucose or other non-protein solids in the plasma of many avian species (4). Pigeons have higher glucose concentrations in their plasma than most mammals, perhaps contributing to higher protein results by refractometry reported by the authors (1).

Lastly, I believe Ref. 12 is incorrect (3). That article does not contain any information about comparative accuracy of refractometry in various species. Perhaps they meant to cite a review article written by me containing that information (2).

FOOTNOTES


Address for reprint requests and other correspondence: J. W. George, 1126 Haring Hall, UC-Davis, Davis, CA 95616 (e-mail: jwgeorge{at}ucdavis.edu)

REFERENCES

  1. Gayathri KL, Shenoy KB, Hegde SN. Blood profile of pigeons (Columba livia) during growth and breeding. Comp Biochem Physiol A Mol Integr Physiol 138: 187–192, 2004.[CrossRef][Medline]
  2. George JW. The usefulness and limitations of hand-held refractometers in veterinary laboratory medicine: an historical and technical review. Vet Clin Pathol 30: 201–210, 2001.[ISI][Medline]
  3. George JW, O'Neill SL. Comparison of refractometer and biuret methods for total protein measurement in body cavity fluids. Vet Clin Pathol 30: 16–18, 2001.[ISI][Medline]
  4. Harr KE. Clinical chemistry of companion avian species: a review. Vet Clin Pathol 31: 140–151, 2002.[ISI][Medline]
  5. Lumeij JT, Maclean B. Total protein determination in pigeon plasma and serum: comparison of refractometric methods with biuret method. J Avian Med Surg 10: 150–152, 1996.
  6. Spagnolo V, Crippa V, Marzia A, Sartorelli P. Reference intervals for hematologic and biochemical constituents and protein electrophoretic fractions in captive common buzzards (Buteo buteo). Vet Clin Pathol 35: 82–87, 2006.[ISI][Medline]
  7. Stämpfli H, Taylor M, McNicoll C, Gancz AY, Constable PD. Experimental determination of net protein charge, [A]tot, and Ka of nonvolatile buffers in bird plasma. J Appl Physiol 100: 1831–1836, 2006.[Abstract/Free Full Text]

Jeanne W. George
 Veterinary Microbiology, Pathology and Immunology, School of Veterinary Medicine, University of California-Davis, Davis, California





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