Heme synthesis and erythrocyte life span in the cat

Establishment of a feline glycated hemoglobin reference interval for a novel dried-blood-spot assay and the effects of anemia on assay results

BACKGROUND

Glycated hemoglobin A1c (HbA1c) reflects long-term (months) glycemic control and has been previously investigated as a monitoring and diagnostic tool in diabetic cats. However, a standardized, reliable, and globally available test and reference intervals (RIs) have not been established. A novel dried-blood-spot card system (A1Care, Baycom Diagnostics) allows for easy collection and evaluation of HbA1c levels in feline patients.

OBJECTIVE

We aimed to establish an RI for HbA1c values in healthy adult cats using the A1Care (Baycom Diagnostics) dried-blood-spot card system.

METHODS

Forty-one healthy client-owned adult cats were enrolled in this study. The RI for HbA1c was calculated according to the recommendation of the American Society for Veterinary Clinical Pathology.

RESULTS

The A1Care HbA1c RI for cats was determined to be 1.9%-3.1%. In healthy cats, A1Care HbA1c values were positively correlated with age (Spearman rho = 0.4 [95% CI 0.1 to 0.6], P = 0.01). In 50% of anemic cats, the A1Care HbA1c value was above 3.1%. There was a weak negative correlation between the A1Care HbA1c value and PCV (Spearman rho = -0.4 [95% CI -0.6 to -0.1]).

CONCLUSIONS

This study established an RI for HbA1c in healthy adult cats similar to previously reported RIs. Future clinical studies are necessary to substantiate that this RI can differentiate diabetic from nondiabetic cats. Further long-term clinical studies will be valuable to determine if HbA1c values can be used as a screening test for prediabetes in cats.

Erythrocyte life span in growing swine as determined by glycine-2-C14

Red blood cell survival studies were performed on five normal growing swine by following the C(14)-specific activity of hemoglobin and heme after the administration of glycine-2-C(14). The erythrocytes of normal growing swine appear to be destroyed both by a random and an age-dependent process. Random destruction accounts for the larger portion of the cells which are destroyed. The "mean" red cell survival time was 62 days. This represents the interval from the time of incorporation of 50 per cent of the maximal amount of labelling achieved to the time when the level had decreased once more to the 50 per cent amount. The " 'corrected' average potential life span" of the red cells was 86 +/- 11.5 days. This figure was obtained by subtracting the number of days required to attain 80 per cent of the maximal labelling from the average survival time of red cells destroyed by an age-dependent process as distinguished from random destruction.

ESTIMATION OF THE LIFE SPAN OF RED BLOOD CELLS

A modified method for fitting the model of Shemin and Rittenberg to study the life span of red cells is described. In this modification the assumption that incorporation of tag is complete before any cells die is relaxed. A recursion formula useful for fitting the model on the digital computer is given. Good results were obtained with data from the sheep, rat, cat, rabbit, and the dog, whereas in several of these cases the method of Shemin and Rittenberg was not satisfactory. By varying critical parameters of the model a continuum of curves is possible. Curves which formerly were explained on the basis of random death can be obtained without this assumption. Limitations and implications of the method are discussed.

An analytical study of in vivo survival of limited populations of animal red blood cells tagged with radio-iron

Animal red blood cell in vivo survival curves, obtained by the radioiron tagging of populations of approximately the same age followed by the administration of non-radioactive iron to suppress radioiron reutilization, have been subjected to mathematical analysis on the basis of the three following assumptions:- (A) Red blood cells disappear from the circulation as the result of senescence: there is an average life span around which the life spans of individual cells are distributed in the usual way. (B) Red blood cells may be removed from the circulation by a process of random destruction which continuously removes a constant fraction of the cells present at any moment irrespective of age or other characteristics. (C) Under the conditions of the experiments described, a fraction of the radioiron, constant for each animal, is reutilized in new red cell formation when released by red cell destruction. This mathematical analysis indicates the following average life spans with the respective standard errors of the mean: dog 107 days +/- 1.14; rabbit 67.6 days +/- 1.94; cat 68.4 +/- 1.50. The mathematical treatment presented has permitted a consideration of the theoretical variation of red cell life spans which was found in these experiments to be relatively small for all three species studied. In the rabbit and cat 2.5 per cent of tagged populations of red cells of the same age would theoretically have disappeared by senescence 17 days before the average life span was reached. The variation of red cell life in the dog was slightly less. Animals of the three species studied, in spite of apparently normal health, exhibited varying degrees of random destruction of both autogenous and transfused fresh normal homologous red cells. As yet, we have no explanation for this random loss of cells occurring in apparently healthy normal animals. The method of mathematical analysis presented is applicable to animal red cell survival studies employing radioiron in which differing rates of random destruction are operating in the removal of red cells.