ANNUAL PREVENTIVE HEALTH SCREENING

 

W. Jean Dodds, DVM

Hemopet

938 Stanford Street

Santa Monica,  CA 90403

310-828-4804; Fax 310-828-8251

 

 

Background

 

Maintaining health and longevity of today’s companion animals requires not only careful observation of the dogs overall well-being on a regular basis, but also depends upon annual preventative health examination and screening by your veterinarian.  A preventive health program should include annual blood and urine profiles, and regular maintenance dental and ear cleaning, along with routine grooming and toenail trimming. This type of annual examination is especially important for senior companion animals over seven years of age. If the preventive health examination and testing reveals some outward or underlying disease process, more sophisticated testing with ultrasonography, radiology, and cardiology, and/or more specific diagnostic laboratory testing for the suspected condition can be performed.

 

Today, with the availability of on-site and referral diagnostic laboratories, and the ability to transmit radiographs and electrocardiograms by computer-technology, experts in various parts of the country can provide input to the local veterinary practitioner. This allows your veterinarian to restore optimum health to your dog as soon as possible.

 

Laboratory Screening  of  Senior Dogs

 

As laboratory tests play an important role in the overall evaluation of animal patients, clinical study of routine laboratory parameters has been conducted to document the findings in healthy senior dogs. As an animal ages, there is a definite loss of functional reserve capacity of every organ system. These changes of aging may affect laboratory data without necessarily reflecting the presence of a disease process and should be considered when interpreting laboratory values in senior patients.

 

There are numerous metabolic and physical effects of aging.  Metabolic effects include: 30-40% reduction in caloric needs because of decreased metabolic rate and activity; decreased immune competence, and less resistance to infections; increased incidence of autoimmune diseases; and a compensatory increase in the function of most endocrine organs (thyroid, reproductive, pancreas).   Physical effects are far ranging: more body weight made up of fat; tissue mass is reduced and tissues lose their elasticity (skin, bone, muscle and cartilage, stomach lining, liver, loans, kidneys, nervous system, and bone marrow); footpads are thickened and toe nails may become brittle; dental calculus increases, gums retract, and there is tooth loss; for intact animals, prostate and ovaries enlarge, but testicles shrink; and there is decreased cardiac output, with increased scarring of heart valves.

 

 

Results of the health profiling in 100 healthy senior dogs indicated that 15 (17%) dogs had an increase in their liver-adrenal function enzyme, alkaline phosphatase (ALP).  Four of them also had increased urine cortisol:creatinine ratios (UCCR), suggesting the possibility of hyperactive adrenal glands (Cushing’s syndrome), and 3 of the 4 were confirmed to have  pituitary-dependent Cushing’s disease by the low-dose dexamethasone suppression (LDDS) test.

In 26 (29%) dogs, the total T4 thyroid values were below normal, and 9 of 11 dogs evaluated further with more complete thyroid function tests were diagnosed with hypothyroidism. This finding underscores the need for complete thyroid profile testing and not just a T4 screening test.

Eleven (11%) dogs had bacteria and pus in their urine. Four of them had elevated blood [chemistry kidney blood chemistry values, thus highlighting the importance of performing a urinalysis, as part of the routine health assessment.

Thus, despite the fact that these dogs were not being treated for any underlying medical problems, clinically significant disease was found in more than 20% of them.

 

Routine Laboratory Profiles

 

The descriptions below outline the basic testing required for a comprehensive annual wellness examination:

 

Complete Blood Count (CBC)

 

The CBC reflects the output of blood cells from the bone marrow and lymph nodes, and of blood cell stored in the spleen and liver. It includes: the white blood cell count (WBC), red blood cell count (RBC), hemoglobin (HGB), hematocrit (HCT), red blood cell indices (MCV, MCH, MCHC), and platelet estimate and/or platelet count.  The differential count examines the number of specific types of white blood cells, namely, neutrophils, lymphocytes, monocytes, eosinophils, and basophils.            

                                                                                                 

Superchem Panel

 

A series of serum chemistry tests is run to help assess various body organs and functions. In several instances, the same test analyte reflects the effects of more than one organ function.

 

Liver Function  Tests that measure or are influenced by liver function include: aspartate aminotransferase (AST, formerly SGOT), alanine aminotransferase (ALT, formerly SGPT), total bilirubin (direct and indirect), alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), cholesterol, and albumin.  

 

Kidney Function  Tests that measure or are influenced by kidney function include: blood urea nitrogen (BUN), creatinine, calcium, phosphorus, albumin, and amylase.

 

Gastro-Intestinal Function Tests that measure or are influenced by gastro-intestinal function include: total protein, albumin, total bilirubin, amylase, lipase, triglycerides, sodium, potassium, and chloride.

 

Pancreatic Function Tests that measure or are influenced by pancreatic function include: amylase, lipase, and glucose.

 

Adrenal Function   Tests that measure or are influenced by adrenal function include: alkaline phosphatase (ALP), sodium, and potassium,  plus other more specific dynamic tests of adrenal activity.

 

Muscle Function   Tests that measure or are influenced by muscle function include: creatine phosphokinase (CPK) or creatine kinase (CK), calcium and corrected calcium [the true concentration of calcium in dogs has to be corrected  (adjusted upwards) whenever the albumin concentration is below 3.5 g/dL], magnesium (not a useful diagnostic aid in dogs), aspartate aminotransferase (AST, formerly SGOT), and alanine aminotransferase (ALT, formerly SGPT).

 

Immune System Function       Tests that measure or are influenced by immune function include:

globulins and lymphocytes.

 

 

Complete Thyroid Profile

  

A complete thyroid profile is needed, at least initially, to screen healthy breeding stock for autoimmune thyroiditis and to diagnose hypothyroidism. Routinely screening with only a T4 test or using an in-office T4 test is not sufficient to rule in or rule out thyroid dysfunction.  A minimum profile of just T4 and freeT4 may be acceptable, when monitoring adequacy of dose for a dog taking thyroxine supplement --- if he/she did not have thyroiditis when tested within the previous year, or if the cost of more complete testing is of serious concern. 

 

The complete thyroid profile includes: T3, T4 , Free T3, Free T4 ,T3 autoantibodies,T4 autoantibodies, and thyroglobulin autoantibodies. The freeT4 assay can be measured by several valid methods, although the most commonly used are an analog radioimmunoassay or the two-stage equilibrium dialysis (ED) radioimmunoassay.  Canine endogenous thyroid stimulating hormone (TSH) can also be measured, but it is poorly predictive of primary hypothyroidism in dogs (70%), and can give 20-40% discordant results [both false positive and false negative]. This finding has been verified by several published studies. The reason is unclear, but it appears that the dog has some alternate pathway for regulating thyroid stimulation.

 

 

Interpreting and Treating Thyroid Dysfunction                                                                                                                                                

All animals are not the same

 

·        Puppies have higher basal thyroid levels than adults

·        Geriatrics have lower basal thyroid levels than adults

 

Thyroxine treatment is best given twice daily

 

·        Dividing the daily dose every 12 hrs avoids undesirable “peak and valley” effect

·        Achieves better steady state over 24 hrs; thyroxine half life is 12-16 hrs

·        Dosing should be given directly by mouth rather than in food bowl

 

      Testing animals on thyroxine therapy

           

·        Blood samples should be drawn 4-6 hrs post-pill for twice daily therapy

·        Minimum testing needed is T4 and freeT4

·        Thyroid antibody profile preferred; a must for all thyroiditis cases

 

Screening for Canine Thyroid Dysfunction

 

·        Complete thyroid antibody profile preferred

·        TSH poorly predictive in dogs (~ 70%) as compared to humans

·        Basal levels affected by certain drugs (steroids, Phenobarbital, sulfonamides)

·        Basal levels lowered by estrogen; raised by progesterone

            [sex hormonal cycle effects], so test intact bitches during anestrus

 

Screening for Canine Autoimmune Thyroiditis

 

·        Complete thyroid antibody profile required

·        Test intact bitches during anestrus

·        Need T3AA, T4AA, TgAA; not  just freeT4, TSH, TgAA

·        OFA Thyroid Registry is limited panel

·        Some cases (~8%) are T3AA and/or T4AA positive, but TGAA negative

 

Treating Canine Autoimmune Thyroiditis

 

·        Treat all cases positive for T3AA and/or T4AA, or TgAA

·        Don’t wait until dog gets ill or has aberrant behavior

·        If only low-grade TgAA positive , retest profile in 2-4 mos

·        Treat with thyroxine twice daily; retest profile in 2-4 mos

·        Always monitor with thyroid antibody profile

 

Do NOT breed dogs with autoimmune thyroiditis

 

·        Heritable trait, regardless of clinical status

·        Screen relatives annually from puberty

·        Consider for breeding, if negative, after age three

 

 

 

[References available upon request ]