Calcium, Serum

DEFINITION

Essential mineral with important regulatory functions (cell signaling). Serum total calcium includes protein-bound (35%), anioncomplexed (10%), and ionized (55%) fractions.

TYPICAL NORMAL RANGE

• Total Ca²⁺: 8-11.5 mg/dL (2-3.8 mmol/L)

• Ionized Ca²⁺: 4.5-6 mg/dL (1.1-1.5 mmol/L)

• Unit conversion: mg/dL × 0.2495 = mmol/L; mEq/L × 0.5 = mmol/L

PHYSIOLOGY

Serum levels are regulated by parathyroid hormone (PTH) and calcitriol (vitamin D metabolite) affecting intestine, kidney, and bone. Dietary absorption depends on calcitriol. Glomeruli filter nonproteinbound Ca²⁺; 98% reabsorbed by tubules. Low ionized Ca²⁺ stimulates PTH production, mobilizing Ca²⁺ from bone, increasing renal tubular resorption, stimulating calcitriol synthesis.

CLINICAL APPLICATIONS

CAUSES OF ABNORMALLY HIGH LEVELS: Hypercalcemia of malignancy, hypoadrenocorticism, primary hyperparathyroidism, osteolysis, granulomatous conditions, hypervitaminosis D, renal failure, excess supplementation (rare from oral supplementation alone) NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Measure ionized Ca²⁺. If ionized hypercalcemia, evaluate for neoplasia (including rectal palpation for anal sac neoplasm in adult dogs), exposure to oral vitamin D (rodenticides, supplements, ointments). Measure serum phosphorus, parathormonerelated peptide, PTH.

CAUSES OF ABNORMALLY LOW LEVELS: Hypoalbuminemia, renal failure, pancreatitis, puerperal tetany, hypoparathyroidism, severe tissue trauma, ethylene glycol intoxication, exocrine pancreatic insufficiency, malabsorption syndromes, hypomagnesemia, phosphate enema, acute tumor lysis syndrome

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: Measure ionized Ca²⁺, serum albumin levels. Evaluate for renal failure, gastrointestinal diseases. Measure serum PTH, magnesium levels.

SPECIMEN AND PROCESSING CONSIDERATIONS

DRUG EFFECTS ON LEVELS

• Increase: thiazide diuretics, supplements containing vitamin D, rodenticides, excess oral phosphate binders

• Decrease: furosemide, glucocorticoids, phosphate enemas, Ca²⁺-binding anticoagulants

SPECIMEN

• Serum (red-top tube) preferred; heparinized plasma (green-top tube) may be used.

• Ionized Ca²⁺: anaerobic handling necessary. Harvest serum or plasma within 1 hour. Stable in heparinized blood for 9 hours (4○C), serum or plasma for 1 week (4○C). Do not use serum separator tubes. Heparin concentration should not exceed 15 U/mL of blood.

RELATIVE COST: $ (serum calcium, single test); $$ (as part of serum electrolyte profile); $$ (ionized calcium)

PEARLS

• Use of correction formula in hypoalbuminemic dogs no longer recommended because of inaccuracy; measure ionized Ca²⁺ instead.

• Acidosis increases ionized serum Ca²⁺ concentration; alkalosis decreases it. Acid-base status affects signs associated with hypocalcemia.

AUTHOR: ROBIN W. ALLISON

Canine Distemper Testing

DEFINITION

Canine distemper is a multisystemic disease caused by canine distemper virus (CDV), a Morbillivirus.

TYPICAL NORMAL RANGE

Refer to laboratory conducting the tests. Available tests include serum immunofluorescent antibody test (IFA) titer, direct IFA, and viral neutralization assay.

PHYSIOLOGY

Distemper is spread via inhalation. Virus attaches to upper respiratory tract epithelium and replicates in macrophages. It spreads to regional lymph nodes and subsequently to bone marrow, thymus, spleen, mesenteric lymph nodes, and gastrointestinal tract. Then 8-14 days later, it spreads to epithelial tissue and the central nervous system, at which time it becomes most easily detected with clinical diagnostic tests. Young dogs may develop fever, leukopenia, respiratory signs, and demyelinating encephalomyelitis. Viral persistence is associated with chronic encephalitis.

CLINICAL APPLICATIONS

CAUSES OF ABNORMALLY HIGH LEVELS:

• Positive IFA immunoglobulin (Ig) M titer indicates recent exposure to vaccine or acute natural infection. IgM is detectable from 1-4 weeks post exposure. Positive IFA IgG titer indicates exposure to vaccine, presence of maternal antibody, or chronic natural infection. Serum viral neutralization assay is preferred for determining protective antibody response to vaccination.

• Positive direct IFA on Cytologie or histopathologic sample is diagnostic of infection.

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Direct immunofluorescence is used for detecting antigen in Cytologie smears of conjunctival, tonsillar, genital, or urinary bladder epithelium, or in white blood cells (buffy coat or bone marrow). Cerebrospinal fluid (CSF): increased protein and lymphocytic pleocytosis are common. Increased anti-CDV antibody in CSF not contaminated with serum is a sensitive and specific indicator of distemper encephalitis. PCR testing can be performed on CSF, ocular or nasal swab, whole blood, or tissue. Routine Cytologie evaluation of conjunctival smears for inclusions (routine staining, with or without IFA) is generally unrewarding.

CAUSES OF ABNORMALLY LOW LEVELS: Lack of protective vaccine antibody titer. Early infection with natural exposure.

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: If clinically indicated, evaluate IgM titer or repeat IgG titer in 2-3 weeks (expect increase if original low/absent level was due to early infection).

SPECIMEN AND PROCESSING CONSIDERATIONS

SPECIMEN: Serologie test: 1 mL of serum (red-top tube). May store 4 days refrigerated or up to months frozen. IFA: conjunctival, urinary sediment, buffy coat smears air dried and preferably fixed in acetone for 5 minutes. Whole blood in EDTA (lavender-top tube) stored for no more than 48 hours refrigerated may be used in place of buffy coat smear. PCR: Minimum 0.5 mL of CSF or whole blood in EDTA (lavender-top tube). RELATIVE COST: $$ (IFA, PCR)

PEARLS

• Serologie testing is the most sensitive and specific test in the live patient: IgM titers rise early in infection and, barring a recent history of vaccination, are specific to infection.

• Although studies suggest that currently available commercial vaccinations offer protection from disease for 3 years, determination of protective serum titer values has not been done. Immunologically competent dogs that have been vaccinated should be able to mount an anamnestic response that would prevent viral exposure leading to disease.

AUTHOR: PATTY J. EWING

Canine Parvovirus Tests

DEFINITION

Canine parvoviral enteritis is a highly infectious, often fatal disease of Canidae caused by a small, nonenveloped DNA virus, CPV-2, that requires rapidly dividing cells for replication.

SYNONYM

Parvo

TYPICAL NORMAL RANGE

Negative or positive with titer. Available tests: serum immunoglobulin (Ig)M and IgG immunofluorescent antibody (IFA), serum antibody by hemagglutination inhibition (HI), fecal antigen ELISA, and electron microscopy for identification of parvovirus particles.

PHYSIOLOGY

Following oronasal exposure to contaminated feces, CPV-2 replicates in oropharyngeal lymphoid tissue, mesenteric lymph nodes, and thymus. Viremia develops 1-5 days post exposure, without enteric shedding. Virus infects intestinal crypt epithelium, causing necrosis and clinical signs that may include lethargy, anorexia, vomiting, and bloody diarrhea. Virus spreads to lymphoid tissue and bone marrow, causing necrosis, subsequent leukopenia, and immunosuppression. Without treatment, secondary infection, gram-negative sepsis, and death may ensue.

CLINICAL APPLICATIONS

CAUSES OF ABNORMALLY HIGH LEVELS:

• Positive fecal ELISA test indicates viral antigen shedding due to natural infection or recent (5-12 days) vaccination with modified live vaccine.

• Positive serum IgM by IFA indicates recent exposure (natural or vaccination); usually positive by the time clinical signs are present.

• Positive IgG titer by IFA indicates exposure (natural or vaccination); can demonstrate rising titer in acute and 10- to 14-day convalescent serum samples, although urgency of initial diagnosis and treatment usually minimizes utility of this approach.

• Serum antibody titer by HI of =1:64 indicates previous exposure (natural or vaccination) and protective antibody.

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Positive fecal ELISA with appropriate clinical signs is generally diagnostic.

CAUSES OF ABNORMALLY LOW LEVELS

• Negative fecal ELISA indicates uninfected, very early postexposure, or end of viral shedding (virus seldom detectable 10-12 days after natural infection; 5-7 days of clinical signs).

• False-negative fecal ELISA may occur if the sample is obtained ex vivo (e.g., defecated stool) rather than being swabbed from the rectum.

• Negative serologic result indicates lack of exposure to virus and inadequate vaccine protection.

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: If clinical signs and laboratory findings are consistent, but ELISA and IFA are negative, electron microscopic exam of feces can be performed. Additional tests—such as histopathologic evaluation of necropsy or biopsy tissue, or tissue culture—are possible but are invasive and potentially hazardous to the patient.

SPECIMEN AND PROCESSING CONSIDERATIONS

LAB ARTIFACTS THAT MAY INTERFERE: Severe hemolysis and lipemia interferes with IFA.

SPECIMEN: ELISA: fresh fecal swab stored for =48 hours (2○C-8○C). HI, IFA: serum (red-top tube), can be stored at 2○C-8○C up to 4 days.

RELATIVE COST: $$ (ELISA, IFA)

PEARLS

Some (but not all) ELISA tests for canine parvovirus will also detect feline parvovirus (panleukopenia) in the feces of cats that are shedding virus. False-negative results occur in early stages (prior to fecal shedding) or late stages (virus has become bound to specific antibody). Positive results due to vaccination may occur in cats for up to 2 weeks post inoculation.

AUTHOR: PATTY J. EWING

Casts in Urine Sediment

DEFINITION

Coagulum of protein, cells, and/or cell debris forming in renal tubules and observed during microscopic examination of urine sediment

SYNONYM

Cylindruria

TYPICAL NORMAL RANGE

• Reported as negative or average number of casts per low-power microscope field with cast identification

• Up to two hyaline casts in moderately concentrated urine (e.g., specific gravity >1.020) is considered normal.

PHYSIOLOGY

Tamm Horsfall mucoprotein, secreted by renal tubular epithelium, combines with cells in renal tubules, forming cylindrical structures (casts) that are passed in urine. This type of cast is occasionally referred to as a hyaline cast. Some casts (granular, cellular, fatty) are composed of renal tubular epithelial cells or material that reflects their degeneration. Waxy casts are uncommon and indicative of chronic kidney disease. They form from granular casts that have degenerated. Others are composed of leukocytes or red blood cells, indicating inflammation or hemorrhage, respectively.

CLINICAL APPLICATIONS

CAUSES OF ABNORMALLY HIGH LEVELS: Toxic renal tubular injury, pyelonephritis

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Evaluate history for exposure to renal toxins; kidney biopsy if otherwise clinically indicated.

SPECIMEN AND PROCESSING CONSIDERATIONS

DRUG EFFECTS ON LEVELS: Gentamicin, amikacin, or other renal tubular toxins may cause granular, cellular, or fatty casts.

LAB ARTIFACTS THAT MAY INTERFERE: Delay in examination, excessive specimen mixing, and alkaline urine promote disintegration of casts and false-negative results.

SPECIMEN: Fresh urine (at least 10 ml) in clean, sterile container for urinalysis RELATIVE COST: $ (reported as part of urinalysis)

PEARLS

Failure to see casts does not rule out renal tubular disease.

AUTHOR: LOIS ROTH-JOHNSON

Cerebrospinal Fluid (CSF) Analysis

DEFINITION

Cerebrospinal fluid (CSF) is the aqueous fluid that surrounds the brain and spinal cord. Pleocytosis refers to an increased cellularity of the CSF sample. Xanthochromia refers to a yellow discoloration of the sample, typically from blood that has been present in the CSF for days or longer. Albuminocytologic dissociation refers to a disproportionate elevation of CSF protein compared to minimally elevated or normal CSF cell count.

TYPICAL NORMAL RANGE

Dogs: red blood cell (RBC), <30/μL; white blood cell (WBC), 0-4/μL; protein, <35 mg/dL. Cats: RBC, <30/μL; WBC, 0-4/μL; protein, <36 mg/dL.

PHYSIOLOGY

CSF provides support and protection for neural structures, serves as a transport medium for metabolic products to and from the brain, and provides a barrier to control the microenvironment of the nervous system. It is normally colorless, clear, and almost acellular. Cytocentrifugation is required for cytologic evaluation of cells to assess for inflammation, hemonhage, and infectious agents. Protein (primarily albumin) concentration is normally very low and requires microprotein assays for accurate assessment.

CLINICAL APPLICATIONS

CAUSES OF ABNORMALLY HIGH LEVELS

• Increased protein: hemorrhage, increased permeability of the blood-CSF barrier, or localized production of immunoglobulins

• Increased protein with normal cellularity: trauma, degenerative disease, intervertebral disc disease, fibrocartilaginous embolism, cervical spondylomyelopathy, neoplasia, and viral infections

• Increased protein and cell counts: inflammation, infection (viral, fungal, protozoal, bacterial, rickettsial, parasitic), granulomatous meningoencephalitis, steroid responsive meningitis, neoplasia, immune mediated disease, vasculitis, and necrotizing meningoencephalitis. Neoplastic cells are rare in CSF; lymphoma is the most commonly identified neoplasm.

NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Correlate CSF findings with history, general physical, neurologic, and radiographic findings.

SPECIMEN AND PROCESSING CONSIDERATIONS

DRUG EFFECTS ON LEVELS: Glucocorticoids may reduce inflammatory cell counts after 24 hours of initiation of treatment, but glucocorticoid treatment may be initiated for patient stabilization if a high degree of steroid-responsive disease exists. Provided CSF tap occurs within 24 hours, accurate CSF cell counts are expected.

SAMPLE FOR COLLECTION AND ANY SPECIAL SPECIMEN HANDLING NOTES: Fluid in EDTA (lavender-top tube) or plain red-top tube; refrigerate. Analysis should be performed as soon as possible; cells deteriorate and lyse rapidly because of the low protein concentration. Addition of autologous serum to CSF (1:1) helps preserve cells for cytologic evaluation. However, a separate aliquot of CSF must be submitted for protein determination and cell counts.

RELATIVE COST: $$

AUTHOR: RUANNA GOSSETT

Chloride

DEFINITION

Major extracellular fluid (ECF) anion. Serum [Cl⁻] essentially equals ECF [Cl⁻]. Na⁺, Hco⁻₃ influence CT concentrations.

TYPICAL NORMAL RANGE

Dogs: 105-115 mEq/L. Cats: 115-125 mEq/L; mEq/L = mmol/L.

PHYSIOLOGY

Major component of gastric juices; intestinal resorption coupled to Na⁺ resorption, Hco⁻₃ secretion. Kidneys play major regulatory role: filtered by glomeruli, reabsorbed in renal tubules following Na⁺ and water. Acid-base balance helps regulate serum levels: inverse relationship between serum [CT] and [Hco⁻₃]. Serum [Na⁺] and [Cl⁻] usually change proportionally, but if [Na⁺] remains the same, increased [Cl⁻] causes hyperchloremic acidosis; decrease causes hypochloremic alkalosis.

CLINICAL APPLICATIONS

PEARLS

Changes independent of [Na⁺] should be interpreted in conjunction with the anion gap. Mixed acid-base disorder is suggested by selective hypochloremia with high anion gap. Most reference laboratory methods are subject to electrolyte exclusion effect artifacts.

AUTHOR: ROBIN W. ALLISON

Cholesterol

DEFINITION

A lipid that is found only in animal tissues. The test measures circulating blood (serum) levels.

Hyperlipidemia is a term that groups hypercholesterolemia and hypertriglyceridemia.

TYPICAL NORMAL RANGE

Dogs: 112-328 mg/dL. Cats: 82-218 mg/dL.

PHYSIOLOGY

Synthesized by the liver or absorbed in intestines from dietary sources. Cholesterol is essential to life as a major component of cell membranes and precursor for synthesis of steroid hormones and bile acids. The liver is the major site of cholesterol synthesis, excretion, and catabolism. Cholesterol and other lipids are insoluble in water. They are transported in the blood attached to apoproteins. Lipid-apoprotein complexes are called lipoproteins. They contain variable proportions of triglycerides, cholesterol, cholesterol esters, and phospholipid. In laboratory analysis, lipoproteins can be separated by ultracentrifugation into chylomicra, high-density lipoproteins (HDL), intermediate-density lipoproteins, low-density lipoproteins (LDL), and very low-density lipoproteins (VLDL), but the clinical importance of lipoprotein profiling in small-animal medicine is minimal compared to human medicine.

Tags: Clinical Veterinary Advisor Dogs and Cats

Jul 24, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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