A Comparison of Blood Glucose and Urine Glucose in Two Cockatiels

Jean R. Gullahorn

4111 Calico Dr. , Cantonment, FL 32533 (USA)

Abstract: Serum and urine glucose concentrations of two cockatiels were determined at various time periods. Analysis of the liquid portion of the droppings by Chemstrip 10SG testing frequently detected glucosuria in the absence of elevated serum glucose values. Thus, the diagnosis of diabetes mellitus in cockatiels cannot be based solely on the presence of glucosuria.

Key Words: Cockatiel, Nymphicus hollandicus, Serum, Urine, Glucose, Chemstrip 10SG

Introduction

Too often birds are treated as small cats. They have many similar disease processes but birds have their own unique pathology as well. The same can be said of the interpretation of laboratory results. The finding of glucosuria in a bird may not have the same significance as it would in a cat or dog.

Methods and Materials

Two healthy male cockatiels were used to collect the samples in this study. Cockatiel A was known to be at least 5 years old. Cockatiel B was an adult of unknown age. They were housed separately in adjacent spacious cages and were free fed a cockatiel seed mix, pellets, a mixture of fresh fruits and vegetables, cereal and cheese daily. Commercial florescent lighting was the only light source with the lights turned on at 730am and turned off at 8pm daily. The data for this study was collected at varying times over a 15 day period in October of 1992. Waxed paper was placed on the cage bottoms to facilitate collection. A sterile syringe and needle were used to collect the liquid portion of a fresh dropping. The liquid was immediately placed on the glucose test paper of a urine test strip (a). The cockatiel was then restrained while blood was aseptically collected from the tibiotarsal vein. The blood sample was immediately separated and the glucose value of the serum determined (b). For the purposes of this study a normal blood glucose value was considered to fall within the range of 200 to 450mg/dL. The results of the urine glucose and the blood (serum) glucose comparisons for cockatiels A and B are listed in Table 1. These two birds have seemed healthy prior to, during and since the study. As of October 1999 both birds were reported to be alive and doing well.

Results

The average blood glucose value from cockatiel A was 360.4 mg/dL with a sample variation of as much as 96.9 mg/dL. Utilizing a urine test strip the urinary glucose values varied from negative to 500mg/dL with the glucose renal threshold of approximately 340 mg/dL. When the blood glucose values were lower, the urinary glucose was lower. When the blood glucose was elevated there was an increase in the spill over into the urine and a higher urinary glucose value was obtained.

The average blood glucose value for cockatiel B was 419.3mg/dL which was 58.9mg/dL higher than the average for cockatiel A. As can be seen from the data collected from cockatiel B, when using a urine test strip, each urine sample tested positive for glucose. In fact, out of seven samples six had a glucosuria of 150 mg/dL. The blood glucose varied by as much as 146.4mg/dL in the seven samples but this did not seem to affect the urine glucose values.

Discussion

The kidney performs three main functions: filtration, excretion or secretion, and absorption whereby the body water and solutes are maintained at fairly constant levels. Filtration takes place in the glomeruli, where crystalloids and substances with molecules of medium to small size such as water, sodium, potassium, chloride, inorganic phosphate, glucose, urea, creatinine, uric acid, and metabolic waste products pass through the capillary walls of the glomeruli into the capsule. State of hydration and urine flow influence glomerular filtration rate. Through reabsorption it conserves needed body water, glucose, and other substances (1). The avian glomerulus is smaller, less vascular, and has fewer capillary loops than the mammalian, so it can be expected to filter less per glomerulus. Consequently, the renal corpuscles of birds are more numerous than those of mammals resulting in relatively larger kidneys, ranging from 2 to 26% of body weight, depending on species (2).

The concentration of substances in the urine may be the same, higher, or lower than that in the blood plasma. A lower concentration usually indicates the substance is being reabsorbed by the kidney tubules. Glucose, which is completely filterable, must be reabsorbed. If there is impairment of the tubules or if blood glucose levels are elevated, not all of the glucose may be reabsorbed and some appears in the urine (1). The threshold for glucose to spill over into the urine varies with species. Martindale measured the glucose renal threshold in four fourteen-month-old hens and found the values of 310, 360, 330, and 260mg/100ml plasma in these birds (3, 4).

The avian kidney is characteristically reptilian with a functional renal portal system which collects blood from the hind part of the body and delivers it to the kidneys via the renal portal vein (1,3). Valves control the flow of blood into the kidneys from the renal portal system (4). Studies suggest that acetylcholine stimulates the valves to open. epinephrine increases the rate of filtration but increases the rate of formation of urine only slightly. Adrenal steroid hormones are also thought to be involved in the control of renal function (5). Birds have the ability to switch this system on and off depending on their requirements so that the pattern of blood flow through one kidney can be very different from that through the other kidney at the same time (1,3).

The avian urinary organs consist of paired symmetrical reddish brown kidneys and ureters which transport urine to the cloaca. They are located in the bony depressions of the pelvis on either side of the spine caudal to the lungs. The kidneys have no cortex or medulla and each is made up of 3 lobes, the cranial, middle, and caudal. Each lobe is made of lobules, comprised primarily of cortical tissue with smaller medullary components (1,2,4,6). In each lobule is a central vein around which radiate the nephrons. Wastes, salts, glucose and water filter out of the blood into renal tubules. In the tubules the water, glucose, and salts are selectively reabsorbed into the blood via a network of capillaries surrounding the tubules. The concentrated wastes pass down the tubules to the ureter (1,2) progressively becoming more concentrated through the absorption of water by the walls of the tubules and the walls of the cloaca. Urine is retrogradely moved into the large intestine where water and salts are also absorbed. By the time the urine leaves the body it has combined with fecal material and formed a white or cream colored paste (5).

Avian blood glucose concentration averages about twice that in mammalian blood (1,2). Human blood glucose is equally distributed between the erythrocytes and plasma, while fowl erythrocytes contain very little or no glucose when compared with the plasma. Therefore, fluctuations in the relative portions of cells and blood plasma can cause apparent changes in the circulating glucose even when the plasma level is unaltered. Tissue lesions and blood sampling can cause a decrease in the volume-percentage of erythrocytes resulting in an apparent increase in blood glucose. Infection by Eimeria tenella is accompanied by a rise in whole blood glucose which is entirely due to a fall in volume-percentage of erythrocytes. Significant changes in the volume-percentage of erythrocytes can occur quite rapidly in birds (1).

Most of our knowledge of avian carbohydrate metabolism is derived from studies conducted on the chicken, duck, goose and the pigeon (3). The blood plasma constituents of a normal adult chicken vary chemically depending on ambient temperature, age, time of day, recency of feeding, type of food eaten, sex, health and state of egg production.

Ambient temperature has been shown to alter circulating glucose levels in domestic birds. Hyperthermia induces hyperglycemia by bringing about a volume-percentage decrease of erythrocytes; hypothermia induces hypoglycemia by bringing about a volume-percentage increase. Studies conducted on one-day-old chicks indicate that exposure to a temperature of 20'C leads to decreased plasma glucose levels of up to 20 percent. Pigeons exposed to 48'C for a few hours had an increase in plasma glucose. The changes observed are a reflection of altered requirements and rates of carbohydrate reactions (1).

Blood glucose levels drop with age. Eighteen-months-old chickens have only 80 percent of the blood glucose seen in those that are three months old (1,2). Studies involving chickens have shown blood glucose rhythms. Daylight blood glucose levels were significantly higher than night time levels. The impact of these rhythms should always be considered when assessing blood glucose (1).

In feeding studies, depriving birds of food for 24 hours resulted in no noticeable fall in the plasma glucose. After 48 hours of fasting the glucose level fell approximately 30 percent in some birds. However, at 72 hours the glucose level had returned to within 15 percent of normal (3).

In healthy males and immatures of both sexes the volume percentage of erythrocytes is fairly stable (3). Sex related differences in glucose levels of whole blood in chickens have been demonstrated with male birds having lower glucose levels than females. Androgen injection markedly increases the packed cell volume of chicken blood. The administration of testosterone to capons causes an increase in the hematocrit, which results in lowering the plasma volume percentage and therefore the amount of organic substances such as glucose dissolved therein (1).

Adrenaline and noradrenaline do not act in fowl exactly as they do in mammals. Conflicting results exist as to whether a "stress related hyperglycemia" occurs in birds. While exogenous cortisone has no effect on avian plasma glucose, hydrocortisone is a powerful hyperglycemic stimulant (3). "Steroid diabetes" has been produced in 8 week old cockerels. These birds exhibited various levels of hyperglycemia, lipemia, retarded body growth, and glucosuria (1,4). Medications such as medroxyprogesterone acetate can have severe side-effects including glucosuria (4).

Glucosuria is frequently seen in psittacine hens with egg-related peritonitis (4). Hypothyroidism results in a mild hypoglycemia whereas hyperthyroidism results in hyperglycemia (1).

Avian insulin is very similar to that of most mammalian insulins, but the level of insulin found in the avian pancreas is about one-tenth of normal mammalian levels. A high glucose challenge results in a sluggish release of insulin in response. Taking into account the poor insulinogenic potential of the pancreas and the persistent "hyperglycemia" normally found in birds, researchers have concluded that the control of avian carbohydrate metabolism by insulin may be of minor significance (7).

The release of prolactin from the pituitary may play a significant regulatory role in carbohydrate metabolism. This release, which occurs during the nesting periods, may be responsible for the associated broodiness, crop secretory activity, restlessness and hyperphagia. Prolactin acts as an antiinsulin agent and reduces pancreatic insulin levels (1).

Urine test strips are made from inert plastic to which is attached different reagent papers. The test papers are attached to the strip with a nylon mesh which holds the reagent paper in place, protects the paper, and provides for a rapid even wetting of the entire test area. The detection of glucose is based on the enzymatic glucose oxidase/peroxidase method. The enzyme glucose oxidase is utilized to catalyze the formation of gluconic acid and hydrogen peroxide from the oxidation of glucose. A second enzyme, peroxidase, catalyzes the reaction of hydrogen peroxide with the chromogen tetramethylbenzidine to form a green dye complex. A color change from yellow to green indicates a positive reaction, with differing intensities of green proportional to the glucose concentration. Sugars other than glucose that may be found in urine were tested and found not to react with the reagent and reducing substances did not give positive results (8).

When utilizing urine test strips in the dog and cat urinary glucose values may be falsely decreased in a refrigerated sample, samples containing large amounts of ascorbic acid, tetracycline, salicylates, mercurial diuretics, and increased urine salt concentrations. Urinary glucose values may be falsely elevated in samples contaminated with hydrogen peroxide or hypochlorite solution. Abnormal proximal renal tubular function due to nephrotoxins, acute renal failure, Fanconi syndrome, or primary renal glucosuria can result in glucosuria. Urinary hemorrhage in a patient with hyperglycemia, blood glucose concentrations exceeding the renal threshold as a result of diabetes mellitus, stress, infusion of dextrose containing fluids, and hyperadrenocorticism are some other causes of glucosuria (9).

Many investigators question the clinical interpretation of results obtained inserting a urinalysis "dipstick" into the liquid component of cloacal output. The fluid portion of the excrement is contaminated by the feces and/or urates. The presence of uric acid or the fecal material may interfere with the dipstick reactions (1,10). Technical services for two different companies (c) that produced urinary dipsticks were contacted regarding this matter and both responses were essentially the same. No studies have been done using "dipsticks" in avian droppings and for that reason neither company can recommend placing validity on any results obtained by doing such.

Conclusion

The results from this study indicate that there can be much individual variation in both the blood glucose and in the urine glucose of cockatiels. Both of these birds were (and to date still are) clinically healthy, had blood glucose values in the normal range, yet utilizing urinary dipsticks, they had glucosuria. A finding of glucosuria in a cockatiel may or may not be significant as there can be many contributing factors. Additionally, one should consider the same possibilities for other avian species. The first step in determining the significance of glucosuria in a patient would be to assess a CBC and serum chemistries. It would be very incorrect to diagnose diabetes mellitus in a bird based solely on the results obtained by inserting a "dipstick" into the liquid portion of a dropping.

Methods and Materials

a. Chemstrip10SG Urine Test Strip

b. utilizing a Vet Test 8008

c. Boehringer Mannheim and Bayer Corporation

References

1. Sturkie PD, Hazelwood RL: Secretion of Gastric and Pancreatic Juice, pH of Tract, Digestion in Alimentary Canal, Liver and Bile, and Absorption; Carbohydrate Metabolism; Kidneys, Extrarenal, Salt Excretion, and Urine; Pancreas, in Sturkie PD (ed): Avian Physiology, 3rd ed, New York, NY, Springer-Verlog New York, Inc, 1976, pp196-232, 263-285, 383-388.

2. Welty JC: The Life of Birds, 2nd ed, Philadelphia, PA, WB Saunders Co, 1975, pp 89-93, 114-115, 134-142.

3. Akester AR, Bell DJ, Clarkson MJ, Richards TG: The Blood Vascular System; Plasma Glucose; The Liver with Special Reference to Bile Formation, in Bell DJ & Freeman BM (ed): Physiology and Biochemistry of the Domestic Fowl, vol 1 & 2, London, England, Academic Press, Inc, 1971, pp 823-828, 913-920, 1104-1113.

4. Ritchie BW, Harrison GJ, Harrison LR: Avian Medicine: Principles and Application, Lake Worth, FL, Wingers Publishing, Inc, 1994, pp 242-244, 538-555, 599-601, 635-637.

5. Petrak ML: Diseases of Cage and Aviary Birds, Philadelphia, PA, Lea & Febiger, 1982, pp 202-204.

6. Steiner, Jr CV, Jr, Davis RB: Caged Bird Medicine, Ames IA, Iowa State University Press, 1981, pp 26-29.

7. Hodges RD: Endocrine Glands, in King AS, McLelland J (ed): Form and Function in Birds, vol. 2, New York, NY, Academic Press, 1980, pp185-187.

8. Chemstrip package insert, Boehringer Mannheim Corporation, Indianapolis, IN.

9. Willard MD: Urinary Disorders, in Willard MD, Tvedten H, Turnwald GH (ed): Small Animal Clinical Diagnosis by Laboratory Methods, Philadelphia, PA, WB Saunders Co, 1989, pp132-133.

10. Sayle RK: Evaluation of Droppings, in Harrison GJ, Harrison LR (ed): Clinical Avian Medicine and Surgery, Philadelphia, PA, WB Saunders Co, 1986, pp156.

This Page Last Updated November 15, 1999

^  Top of page