Fructosamine. Claudia E. Reusch, DVM, PhD, Marianne R. Liehs, Martine Hoyer, and Renate Vochezer

Transcription

1 Fructosaine A New Paraeter for Diagnosis and Metabolic Control in Diabetic Dogs and Cats Claudia E. Reusch, DVM, PhD, Marianne R. Liehs, Martine Hoyer, and Renate Vochezer Fructosaines are glycated seru proteins that, depending on their life span, reflect glyceic control over the previous 2 to 3 weeks. The nitroblue tetrazoliu reduction ethod adapted to autoanalysis appeared to be a practical eans to assay fructosaine quickly, econoically, and accurately. The upper liit of the reference range is 374 pol/l in dogs (95% percentile) and 340 pol/l in cats (95% percentile). Newly diagnosed diabetic dogs and cats that had not undergone previous insulin therapy had significantly higher fructosaine concentrations than nondiabetic anials. In diabetic dogs that were receiving insulin therapy, the fructosaine test reflected the glyceic state far ore accurately than did individual blood glucose easureents. Anials with satisfactory etabolic control revealed fructosaine concentrations within the reference range, whereas fructosaine concentrations above 400 pol/l indicated insufficient etabolic control. On the basis of fructosaine concentrations, cats with a transitory hyperglyceia and cats with diabetes ellitus were differentiated. The fructosaine test is a valuable paraeter for the diagnosis and etabolic control of diabetes ellitus in dogs and cats. (Journal of Veterinary Internal Medicine 1993; 7: ) IN THE PAST etabolic control in diabetic people and anials has been evaluated fro blood and urine glucose easureents. However, because both paraeters indicate the glyceic status only at a given point in tie, they are unreliable arkers for long-ter etabolic control. It was therefore a ajor breakthrough when during the 1970s techniques for easuring glycated heoglobin becae available providing an objective retrospective indication of blood glucose concentrations over the previous 4 to 8 weeks..2 In people, easureent of glycated heoglobin has been adopted as a useful tool for diabetic control. Over the last decade, anial studies showed that also in diabetic dogs and cats the easureent of glycated heoglobin is a useful paraeter in diagnosis and etabolic ~ontrol.~.~.~ Shortly after the developent of HB A, easuring techniques, it was discovered that other seru proteins becoe glycated in an analogous way.6 Due to their shorter life span copared with heoglobin, it was pro- Fro the Departent of Veterinary Internal Medicine, University of Munich, Munich, Gerany. Reprint requests: Claudia E. Reusch, the Departent of Veterinary Internal Medicine, University of Munich, 8000 Munich 22, Gerany. 177 posed that they can be used to reflect glyceic control over the previous 2 to 3 weeks, thus rendering the of great interest for onitoring the results of vigorous diabetes treatent progras. In 1982, Johnson et al. described a new assay for easuring these glycated proteins, referred to as fructosaines. The fructosaine assay is based on the ability of ketoaine-linked glucose residues on glycated seru proteins to reduce the dye nitroblue tetrazoliu. The ter fructosaine refers to the structure of the ketoaine rearrangeent product (1-deoxy- I [-lysyl-albuin]fructose) fored as a result of the non-enzyatic reaction between glucose and the aino group on the lysine residues of the protein. Since the reaction is irreversible, fructosaine concentrations depend on the duration and extent of the hyperglyceia and the half-life of the seru proteins. In people, fructosaine is a frequently deterined and valuable paraeter for the diagnosis and etabolic control of diabetes ellit~s.~,~ Although easureents of glycated seru coponents in experientally induced diabetic dogs were ost proising, its clinical usefulness in veterinary edicine has so far not been established. This study deterined whether the concentration of seru fructosaine akes it possible 1) to

2 178 REUSCH ET AL. Journal of Veterinary Internal Medicine differentiate reliably between diabetic and non-diabetic dogs and cats; 2) to ake a judgent about the etabolic situation in cases of clinically anifest diabetes; and 3) to differentiate between diabetic cats and cats with a transitory hyperglyceia. Control Anials Material and Methods Forty-eight healthy dogs (24 intact ales, 1 neutered ale, 21 intact feales, 2 spayed feales) and 32 healthy cats (1 7 ales and 15 feales, all neutered), all owned by students, were included to establish fructosaine reference ranges. Ages ranged fro 1 to 11 years with a ean age of 5 years for the dogs and fro 1 to 10 years with a ean age of 4 years for the cats. No signs of disease were revealed by physical or coplete heatologic exaination or by urinalysis. Plasa glucose was within the reference range for our laboratory in all anials. Dogs with Diabetes Mellitus During the period fro Septeber 1990 until March 199 1,32 diabetic dogs (6 intact and 1 neutered ales, 2 1 intact and 4 spayed feales) were included in the study. Fourteen of the dogs were newly diagnosed as being diabetic on the basis of being polyuric, polydipsic, and having increased blood and urine glucose concentrations; they had not received any previous insulin therapy. The duration of insulin therapy received by the other 18 dogs varied between 4 weeks and 3 years. Those dogs (n = 24) that had at least three check-ups in a 2-or-ore week period, including a coplete heatologic exaination, blood glucose profile over 12 hours, and fasting fructosaine easureent, were classified into three groups of different glyceic control status: 1 ) dogs with fully satisfactory etabolic control needed fasting blood glucose concentrations of 200 g/ dl or less (n = 7); 2) dogs with oderately satisfactory etabolic control had to have fasting blood glucose concentrations between 200 and 300 g/dl (n = 7); and 3) dogs with poor etabolic control had fasting blood glucose concentrations above 300 g/dl (n = 10). The highest fructosaine value of each dog was chosen to copare the three groups. Cats with Diabetes Mellitus During the period fro Septeber 1990 until March 199 1, nine diabetic cats (all neutered ales) were used for the study, two of the having been newly diagnosed as diabetic and not having received any previous insulin therapy. Their ages ranged fro 8 to 18 years with a ean of 12 years. Diabetes ellitus was diagnosed when the cat was poluric and polydipsic, showed no signs of any other underlying disease, had increased blood and urine glucose concentrations, and responded well to insulin therapy. Only those cats that had at least two check-ups within a four-or-ore week period, with a coplete heatologic exaination, blood glucose profile over a 12-hour period, and fasting fructosaine easureent at the tie of each check-up were included. Cats with Transitory Hyperglyceia Eight cats (1 intact and 1 neutered ale, 3 intact, and 3 spayed feales) with a transitory hyperglyceia were used for coparison with the diabetic cats. Their ages ranged fro 2 to 8 years with a ean age of 6 years. Requireents for inclusion in this group were an initial blood glucose concentration above 150 g/dl, an underlying diagnosed disease, and no clinical signs of diabetes ellitus. Each cat was required to have a iniu of three check-ups. At least two check-ups conducted after the underlying disease had been cured had to reveal blood glucose concentrations within the reference range. Analytical Procedures Blood speciens were obtained fro all anials after an overnight fast. Plasa glucose concentrations were deterined with the glucose oxidase ethod in the dry cheistry laboratory unit*. " Seru fructosaine concentrations were easured? according to the ethod of Johnson et al.' The results are expressed in pol/l. For stability studies, aliquots of seru saples taken fro three dogs and cats were stored at 4 C and at -18 C. Aliquots stored at 4 C were exained daily on 5 consecutive working days, aliquots stored at - 18 C were exained once a week for 4 weeks. Statistical Analysis All results were analyzed by eans of paraeter free statistical ethods.$ The reference ranges were calculated as 95% percentile. Data fro healthy and diabetic dogs and cats were copared using the Wilcoxon ranksu test for two groups. The Kruskal-Wallis test was used to deterine whether differences existed between the three groups of different glyceic control status.12 The level of significance was set to be p < Analytical Procedures Results Iprecision was investigated within and between assay runs using ten aliquots of canine and feline seru saples in each case; coefficient of variability (CV) of within-run iprecision was 2.4% in the dog and 1.1% in *Reflotron, Boehringer Mannhei, FRG. thitachi 705 adapted test kit, Boehringer Mannhei, FRG. $SPSS/PC + V 2.0 Base Manual, SPSS Inc., Chicago 1988.

3 VOI. 7. NO. 3, 1993 FRUCTOSAMINE 179 the cat; CV of between-run iprecision was 3.4% in the dog and 4.0% in the cat. Fructosaine concentrations showed less than 5% variation and therefore were considered constant at 4 C on 5 consecutive days and at - 18 C for 1 onth in all saples. Dogs In healthy dogs, fasting fructosaine concentrations ranged fro 187 to 386 pol/l with a edian of 3 12 pol/l. The reference range was calculated fro 249 to 374 pol/l. Fructosaine concentrations in the group of 14 newly diagnosed diabetic dogs with no previous insulin therapy were significantly higher than values in the noral dogs, ranging fro 325 to 834 pol/l (x: 476 pol/l). Fasting plasa glucose concentrations varied between 290 and 485 g/dl (x: 337 g/dl) (Fig. 1, Table 1). In two of the diabetic dogs, fructosaine concentrations were noral. Their history indicated that the disease had been of short duration. One dog had Cushing's syndroe with poor etabolic control: it had not been hyperglyceic 3 days previously. Polydipsia and polyuna developed in the other dog after estrus. Estrus had been copleted for only 1 week. Figure 2 shows the highest fructosaine values, respectively, of all the 24 diabetic dogs, which were classified into three groups with different etabolic states. All three groups differed significantly fro each other. In the group with fully satisfactory etabolic control, 4 of 7 (57%) of the fructosaine values were within the reference range. The results of the groups with oderately satisfactory and with poor etabolic control overlap to a large extent. Five of 7 (7 1%) and 6 of 10 (60%), fructosaine easureents were between 400 and 500 pol/l, respectively. However, only 1 of 7 (14%) easureents in the group with oderately satisfactory etabolic con jlo1 * * * *** f * x Fr uctoaarnioe healthy dogs diabetic do s polll (""treatede FIG. I. Fructosaine concentrations in healthy and newly diagnosed diabetic dogs. The broken line shows the upper liit of the reference range. 0 healthy dogs (n = 48); * newly diagnosed diabetic dogs (n = 14). 843 TABLE 1. Plasa Glucose and Seru Fructosaine Concentrations in Healthy and Diabetic Dogs ~ Blood Glucose g/dl Fructosaine pol/l Range R Range R Healthy dogs n = Diabetic dogs Untreated n= Well controlled n = 8/ Moderately controlled n = 7/ Poorly controlled n = 10/ trol were above 500 pol/l versus 4 of 10 (40%) in the group with poor etabolic control. Four dogs with diabetes ellitus after estrus were onitored closely after ovariohysterectoy over a 1 - onth period (Fig. 3). Fasting blood glucose and fructosaine concentrations were increased in all four dogs on the day of surgery. In the dog with initially lowest blood glucose and fructosaine concentrations, both paraeters were within the reference range after 1 week. In the other three dogs, blood glucose concentrations had dropped also but fructosaine concentrations were still unchanged. Two weeks after ovariohysterectoy blood glucose was within the reference range in all dogs, and after a further week so was fructosaine concentrations. The different clinical reliability of blood glucose versus fructosaine easureents for reflecting etabolic control is shown for two diabetic dogs that were exained regularly over a 5-onth period (Fig. 4). At the tie of diagnosis, blood glucose and fructosaine values '' fully adsralsly.~ti.i.e1o,y Control..,I.IBFlOry conlrel 000, control groups 01 different etabolic status FIG. 2. Fructosarnine concentrations in diabetic dogs with fully satisfactory, oderately satisfactory, and poor etabolic control. Only the highest fructosaine value ofedch dog is given. The broken line shows the upper liit of the reference range.

4 180 REUSCH ET AL. Journal of Veterinary Internal Medicine 350 ~ ~ week8 atler surgery FIG. 3. Seru fructosaine and plasa glucose concentrations in four dogs after ovariohystectoy. The upper broken line shows the upper liit of the fructosaine reference range, the lower broken line the upper liit of the plasa glucose reference range. were increased. Both paraeters declined as a result of intensive insulin therapy. After 2 onths, both dogs appeared on the basis of fasting blood glucose concentrations to have regained good etabolic control; this was confired in dog nuber two by a decreased fructosaine concentration. Fructosaine in dog nuber one, however, was higher than ever before. This dog s poor glyceic state was revealed by highly increased paraeters at all following check-ups. The dog s owner had been unreliable in adinistering insulin regularly. However, initially he tried to avoid being detected by giving the dog injections just before the dog s appointent at the clinic. Dog nuber two s fasting blood glucose reained near to the reference range. The good etabolic control of this dog was confired by noral fructosaine results each tie and the lack of clinical signs of diabetes ellitus. Cats Fasting seru fructosaine concentrations in healthy cats ranged fro 22 1 to 34 1 pol/l with a edian of 284 pol/l. The reference range was calculated as being between 221 and 340 pol/l. Twenty-six check-ups on a total of nine diabetic cats revealed significantly different fructosaine concentrations (range: pol/l, X: 487 pol/l). Fasting blood glucose ranged fro 136 to 565 g/dl (%: 340 g/dl) (Fig. 5, Table 2). Due to the sall nuber of easureents, the diabetic cats were not classified into groups. The only two newly diagnosed diabetic cats that had not undergone previous insulin therapy had very high fructosaine concentrations of 643 pol/l and of 677 pol/l. Three of the four noral fructosaine concentrations within the diabetic group cae fro two cats with good etabolic control. Two check-ups carried out within a 1-onth period on one of the two cats showed fructosaine concentrations of 300 pol/l and 298 pol/l with acceptable blood glucose concentrations (226 g/dl, 136 g/dl) and no clinical signs of diabetes ellitus. The other cat, which had been receiving insulin therapy for 4 years, had an increased glucose concentration (468 g/dl) while fructosaine was only 266 pol/l. Since according to the owner the cat was not polyuric and polydipsic and had negative urine test sticks ost of the ties, we suspected that the cat s extree hyperglyceia was due to stress at the tie of blood collection. In eight sick cats that were brought to the clinic without any clinical signs of diabetes ellitus but with a variety of other syptos, hyperglyceia was found by chance. The initial blood glucose concentrations ranged between 160 and 240 g/dl. Their fructosaine con- Glucose gldl po1/1 g/dl * M * * * 3%. * * *t *I I840 Fructosalne pol/l FIG. 5. Plasa glucose and seru fructosaine concentrations in healthy and diabetic cats and cats with a transitory hyperglyceia. The broken line shows the upper liit ofthe reference range. 0 healthy cats (n = 32). * diabetic cats (n = 9 with a total of 26 easureents). 0 cats with a transitory hyperglyceia (n = 8). The initial glucose and fructosaine concentrations are given.

5 VOl. 7. NO FRUCTOSAMINE 181 TABLE 2. Plasa Glucose and Seru Fructosaine Concentrations in Healthy and Diabetic Cats and Cats with a Transitory Hyperglyceia Blood Glucose g/dl.fructosaine bol/l Range X Range X Healthy cats n = Diabetic cats n = 9/ Cats with a transitory h ypergl yceia n=8 Initial exa Last exa centrations were between 204 and 350 pol/l (X: 3 I1 pol/l), which was not different fro those of the healthy cats (Fig. 5). After they had been cured of the underlying disease, blood glucose was within the reference range on at least two check-ups. Fructosaine concentrations did not change significantly. Table 2 shows the results of the initial and final blood glucose and fructosaine easureents. Discussion This study indicates that the fructosaine test is a valuable paraeter for the diagnosis and the etabolic control of diabetes ellitus in dogs and cats. Fctosaines can be easured quickly, easily, and econoically using the nitroblue tetrazoliu reduction ethod by eans of autoanalysis. The quality control variation coefficients of less than 5% were well within acceptable liits and the stability tests confired sufficiently long-duration storage capacity for collection of large nubers of saples in a routine laboratory. In 12 of the I4 newly diagnosed diabetic dogs that had not undergone any previous insulin therapy fructosaine concentrations were clearly increased and differed significantly fro those of the healthy dogs. In the two dogs with noral fructosaine concentrations it was plain fro the case histories that the clinical signs had only prevailed for a few days before exaination. Because their blood glucose concentrations did not differ fro those of the other diabetic dogs, we assue that the duration of the hyperglyceia was not sufficient in either of the two anials to cause an increase in protein glycolysation. These findings suggest that the fructosaine test is a useful screening test for diabetes ellitus. Of additional diagnostic interest is a noral fructosaine concentration accopanied by siultaneous hyperglyceia. Cases of secondary diabetes (Cushing s syndroe, progesterone-induced hypersoatatropis, iatrogenic fors) ay be reversed if the basic disease is treated. The fructosaine test furtherore proved to be a well-suited paraeter for judging the quality of insulin therapy. We found significant differences between the groups of dogs that we had classified on the basis of their glyceic control quality as good, oderate or poor, even though the highest fctosaine values were chosen. In diabetic dogs, which we found to have fasting blood sugar concentrations of less than 200 g/dl on at least three check-ups during therapy of at least 6 weeks, ost of the fructosaine easureents were within or close to the noral range. Fructosaine concentrations above 400 pol/l were found, with one exception, only in dogs with insufficient etabolic control. As clearly shown for two dogs in Figure 4, the fructosaine concentration provides uch ore inforation about the actual glyceic state than does the blood sugar concentration, which only reflects the oentary situation. Since fructosaines are fored by irreversible bonding of glucose to seru proteins, the glucose not being released again until the protein is degraded, the concentration of fructosaines in seru reflects the average blood sugar concentration over the preceding two to three weeks8 The paraeter is not influenced by short-duration blood sugar fluctuations such as can be caused by stress at the tie of blood collection, concoitant disorders at the tie of deterination, or the particular kind of discipline practiced by soe anial owners with respect to insulin adinistration and diet. In the cats we exained, too, the fctosaine concentrations of healthy anials differed significantly fro those of the diabetic ones; the upper liit of the reference range was arginally below that of the dog. Although the nuber of cats is too sall to allow a definitive stateent, the results strongly indicate that the fructosaine test is highly suitable for diagnosing diabetes and for evaluating the quality of insulin therapy. The two cats that had been newly diagnosed as diabetic had fructosaine concentrations nearly twice the upper liit of the reference range, whereas the two cats considered to have good etabolic control had fructosaine concentrations within the reference range. In one of the cats the good etabolic control - which was in keeping both with the clinical ipression and the evaluation of the owner - was reflected only by the noral fctosaine concentration, whereas the fasting blood sugar was highly increased on the day of the check-up. We are of the opinion that specifically in cats, which copared with dogs are uch ore influenced by stress, the fructosaine concentration reflects the actual etabolic control quality ore objectively than do sporadic blood sugar easureents. Transient hyperglyceias initiated by the stress of soe other disease in cats do not, according to our findings, result in increased fructosaine concentrations. This eans that on the basis of fructosaine concentrations it is possible to differentiate between diabetic and

6 182 REUSCH ET AL. Journal of Veterinary Internal Medicine transient hyperglyceia, soething which has up till now not been possible by eans of glucose deterination alone. The reliability of the fructosaine test is liited in cases in which the diabetes is a recent developent or in cases of long-duration stress hyperglyceia. Further studies will therefore need to focus on deterining the duration and extent of hyperglyceia necessary to induce an increased rate of protein glycolysation. The fructosaine test is a valuable additional paraeter for the diagnosis and long-ter treatent of diabetic dogs and cats. The fructosaine assay is fast and easy. It should be integrated in the routine laboratory-onitoring of diabetes. References 1. Trivelli LA. Ranney HM. Lai HT. Heoglobin coponents in patients with diabetes ellitus. N Engl J Med ; 284: Santiago JV, Davis JE, Fisher F. Heoglobin Alc levels in a diabetes detection progra. J Clin Endocrinol Metab 1978; Mahaffey EA, Cornelius LM. Glycosylated heoglobin in diabetic and non diabetic dogs. J A Vet Med Assoc 1982; 180: Jung G. Glykosylierte Haoglobine und Blutzuckenverte zur Ubenvachung der diabetischen Stoffwechsellage bei Hund. Munchen, Vet Med Diss Akol KG, Waddle JR. Glycosylated heoglobin quantification in diabetic and non-diabetic cats. Proceedings 9th For ACVlM 1990; Washington DC. 6. Yue DK, Morris K, McLennan S, et al. Glycosylation of plasa protein and its relation to glycosylated haeoglobin in diabetes. Diabetes 1980; 29: Johnson RN, Metcalf PA, Baker JR. Fructosaine: a new approach to the estiation of seru glycosylprotein. An index of diabetic control. Clin Chi Acta 1982; 127: Abruster DA. Fructosaine: Structure, Analysis, and Clinical Usefulness. Clin Che 1987; 12: Hill RP, Hindle EJ, Howey JEA, et al. Recoendation for adopting standard conditions and analytical procedures in the easureent of seru fructosaine concentration. Ann Clin Bioche 1990; 27: Mahaffey EA, Buonanno AM et al. Glycosylated albuin seru protein in diabetic dogs. A J Vet Res 1984; 45: I I. Hirschberger J. Klinische Priifungeines it Trockencheie arbeitenden Laborgerates Reflotron. Tierarztl Prax 1987; 15: Sachs L. Applied Statistics. A Handbook of Techniques. 2nd ed., , Springer Series in Statistics, Springer New York, Berlin, Heidelberg. Tokyo, Cardiac and Abdoinal Ultrasonography in Sall Anials: An Advanced Course October 2-3, 1993 Michigan State University East Lansing, MI For ore inforation, contact the college of Veterinary Medicine Outreach Office, A- 133 East Fee Hall, Michigan State University, East Lansing, MI or call