Hypercortisolism (HC) is a common disease in dogs.  This article will review the laboratory tests that are available for diagnosis of HC and laboratory tests for differentiating between causes of HC.  An emphasis will be made on the clinical process that leads to the decision to perform those tests and common misconceptions and issues that arise when performing them.

To choose between the adrenocorticotropic hormone (ACTH)–stimulation test and the low-dose dexamethasone suppression test (LDDST), the advantages and disadvantages of both tests should be considered, as well as the clinical presentation.  Differentiation of HC from diabetes mellitus, liver diseases, and hypothyroidism cannot be based solely on endocrine tests.  Clinical signs, imaging studies, histopathology, and response to treatment should all be considered.

Endocrine Pancreatic Disorders

• Overview
• Diabetes Mellitus
• Gastrinoma
• Insulinoma

Thyroid Gland Disorders

• Hyperthyroidism
• Hypothyroidism

Adrenal Gland Disorders

• Hyperadrenocorticism
• Catecholamine-Secreting Adrenal Tumors
• Sex Hormone–Secreting Adrenal Tumors
• Hyperaldosteronism
• Hypoadrenocorticism

Pituitary Disorders

• Anatomy and Physiology
• Diseases of the Pituitary Gland

Disorders of Calcium Metabolism

• Calcium Homeostasis
• Approach to the Cat with Hypercalcemia
• Increased Parathyroid Hormone with Hypercalcemia
• Decreased Parathyroid Hormone with Hypercalcemia
• Normal Parathyroid Hormone with Hypercalcemia
• Other Causes of Hypercalcemia
• Treatment of Hypercalcemia
• Hypocalcemia

FIGURE 8-5. Diagnostic approach to hypoglycemia in dogs and cats. ACTH, Adrenocorticotropic hormone; ALT,alanine aminotransferase; CBC, complete blood count; SAP, serum alkaline phosphatase; US, ultrasound; WBC, white blood cell.



Diagnostic evaluation of hypercalcemia in dogs and cats.

The range of serum calcium and phosphorus concentrations for the more common causes of hypercalcemia and for hyperparathyroidism in dogs. HP, Hyperparathyroidism; 2°, secondary.

Range of serum calcium (Ca) and parathyroid hormone (PTH) concentrations for the more common disorders causing alterations in serum calcium or parathyroid gland function.

Diagnostic evaluation of hypocalcemia in dogs and cats. 

Diagnostic approach to persistent or inappropriate hyperglycemia in diabetics treated with insulin. 

Diagnostic approach to hyperlipidemia in the dog and cat.

Evaluation of cats with suspected hyperthyroidism based on history, clinical signs (i.e., weight loss, polyphagia, polyuria-polydipsia, hyperactivity, cervical mass) or laboratory findings (i.e., increased serum alkaline phosphatase [SAP], increased serum phosphorus).

Interpretation of thyroid-stimulating hormone (TSH) stimulation test in dogs. 
 

Endogenous plasma adrenocorticotropic hormone (ACTH) concentrations from clinically normal dogs, dogs with adrenal-dependent hyperadrenocorticism (adrenocortical carcinomas or adenomas), and dogs with pituitary-dependent hyperadrenocorticism.

Endogenous plasma adrenocorticotropic hormone (ACTH) concentrations in normal dogs, dogs with secondary adrenal failure, and dogs with primary adrenal failure.

Evaluation of patients with suspected hyperadrenocorticism based on history (polyuria-polydipsia, polyphagia, panting, weakness), physical examination (truncal alopecia, potbelly, calcinosis cutis, hepatomegaly), or laboratory findings (increased serum alkaline phosphatase [SAP], lymphopenia, eosinopenia, hypercholesterolemia, urinary tract infection). ACTH, Adrenocorticotropic hormone; PDH, pituitary-dependent hyperadrenocorticism; UCCR, urine cortisol : creatinine ratio.

Patterns of plasma cortisol responses during high-dose (0.1 mg/kg) dexamethasone suppression testing in dogs with pituitary-dependent or adrenal-dependent hyperadrenocorticism.

Although veterinary clinicians commonly rely on panels of laboratory tests with individual results flagged when abnormal, care should be taken in interpreting normal test results as well.  There are several examples of this in evaluating patients with endocrine disease.  The finding of a normal leukogram (absence of a stress leukogram) can be indicative of adrenal insufficiency in dogs, and this disorder can be especially elusive when there are no overt indicators of mineralocorticoid deficiency.  

Cats with hyperthyroidism can have normal serum thyroid hormone concentrations, normal hematocrits, and normal serum concentrations of creatinine despite the presence of disease that affects these parameters.  A normal serum phosphorus concentration, in the face of azotemia, isosthenuria, and hypertension can point a clinician toward a diagnosis of primary hyperaldosteronism rather than primary renal disease.  A normal serum parathyroid hormone concentration in the face of hypercalcemia is inappropriate and can indicate the presence of primary hyperparathyroidism.  Similarly, hypoglycemia accompanied by a normal serum insulin concentration can be found in cases of hyperinsulinism.  These normal findings in abnormal patients, and their mechanisms, are reviewed.

• • Acetylcholine Receptor Antibody
  • Activated Coagulation Time (ACT)
  • Activated Partial Thromboplastin Time (APTT)
  • Adrenocorticotropic Hormone (ACTH), Endogenous
  • Adrenocorticotropic Hormone (ACTH) Stimulation Test
  • Alanine Aminotransferase (ALT, Formerly SGPT)
  • Albumin
  • Alkaline Phosphatase, Serum (SAP or ALP)
  • Ammonia
  • Amylase, Serum
  • Anion Gap
  • Antinuclear Antibody (ANA)
  • Arterial Blood Gases
  • Evaluate PaO₂
  • Potential causes of hypoxemia
  • Evaluate pH
  • Assess acid-base status
  • Aspartate Aminotransferase (AST, Formerly SGOT)
  • Basophil Count
  • Bicarbonate (HCO₃⁻)
  • Bile Acids
  • Bilirubin
  • Blood Urea Nitrogen (BUN)
  • Buccal Mucosal Bleeding Time (BMBT)
  • Calcium (Ca)
  • Cerebrospinal Fluid (CSF)
  • Chloride (Cl)
  • Corrected Hyperchloremia (elevation of chloride disproportionate to elevation of sodium):
  • Corrected Hypochloremia (loss of chloride relative to sodium)
  • Cholesterol (CH)
  • Cholinesterase
  • Cobalamin
  • Complete Blood Count (CBC)
  • Coombs Test
  • Cortisol
  • Creatine Kinase (CK, formerly CPK)
  • Creatinine
  • Cytologic Criteria of Malignancy
  • General Criteria
  • Nuclear Criteria
  • Cytologic Features of Discrete Cell (Round Cell) Tumors
  • Discrete Cells (Round Cells)
  • Specific Discrete Cell Tumors
  • Mast Cell Tumor
  • Lymphoma
  • Canine Cutaneous Histiocytoma
  • Malignant Histiocytosis/Histiocytic Sarcoma/Systemic Histiocytosis
  • Plasmacytoma
  • Transmissible Venereal Tumor
  • Melanoma
  • Cytologic Features of Mesenchymal Cells
  • Cytologic Features of Normal Epithelial Cells
  • Cytology of Ear Canal Swabs
  • Bacteria
  • Fungi
  • Mites
  • Neoplasia
  • Miscellaneous
  • Cytology of Nasal Swabs or Flush Specimens
  • Normal Findings
  • Infectious Agents
  • Noninfectious Conditions
  • Dexamethasone Suppression Tests
  • Low-Dose Dexamethasone Suppression Test (LDDST)
  • High-Dose Dexamethasone Suppression Test
  • Disseminated Intravascular Coagulation (DIC), Diagnostic Tests
  • Eosinophil Count
  • Erythrocyte Count (Red Blood Cell [RBC] Count)
  • Folate
  • Fructosamine
  • Gamma Glutamyltransferase (GGT)
  • Globulin
  • Glucose
  • Glucose Tolerance Test
  • Glycosylated Hemoglobin
  • Heartworm Antibody, Feline
  • Heartworm Antigen, Canine
  • Heartworm Antigen, Feline
  • Hematocrit (Packed Cell Volume, PCV)
  • Hemoglobin
  • Hemolysis, Prevention in Laboratory Samples
  • Steps to Prevent Hemolysis:
  • Immunoassays
  • Insulin
  • Iron-Binding Capacity (Total, TIBC)/Ferritin
  • Joint Fluid (Arthrocentesis)
  • Lipase
  • Lymphocyte Count
  • Magnesium (Mg)
  • Mean Corpuscular Volume (MCV)
  • Methemoglobinemia
  • Methods of Sample Collection for Cytology
  • Fine-Needle Biopsy (Aspiration or Nonaspiration Method)
  • Impression Smear
  • Scraping
  • Swab
  • Monocyte Count
  • Myoglobinuria
  • Neutrophil Count
  • Osmolality
  • Packed Cell Volume
  • Parathyroid Hormone (PTH)/Ionized Calcium
  • Phosphorus (P)
  • Platelet Count
  • Polymerase Chain Reaction
  • Potassium (K)
  • Protein, Total (TP)
  • Prothrombin Time (PT)
  • Red Blood Cell (RBC) Count
  • Reticulocyte Count
  • Sodium (Na)
  • Thoracocentesis Fluid
  • Eosinophilic Effusion
  • Thrombocyte Count
  • Thyroid Function Tests
  • Toxoplasmosis Antibody Titer
  • Triglycerides
  • Trypsinogen-Like Immunoreactivity (TLI)/Pancreatic Lipase Immunoreactivity (PLI)
  • Urinalysis
  • Appearance
  • Specific Gravity
  • Chemical Properties
  • Urinary Sediment Examination
  • Urine Cortisol/Creatinine Ratio
  • Urine Protein/Creatinine Ratio
  • von Willebrand Factor
  • White Blood Cell (WBC) Count