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Cryptococcus Antigen Test Crystals, Urine Sediment 1331

Cryptococcus Antigen Test
VetBooks.ir Definition Lab Artifacts

Cryptococcus is an environmental saprophytic, Serum separator tube (SST) gel, lipemia, hemo- Relative Cost: $$
dimorphic fungus with worldwide distribution. lysis, specimen turbidity, and anticoagulants Pearls
The Cryptococcus antigen test detects cryptococcal interfere with testing. • LAT can be used to monitor therapy as
polysaccharide capsular antigen, in the yeast titers should decrease to zero with disease
form, within serum or cerebrospinal fluid (CSF). Specimen Collection and Handling resolution.
• Collect blood in a plain red top tube; do • Titers from different laboratories using dif-
Physiology not use SST. Spin and collect serum. Fasted ferent methodologies can vary considerably;
Inhalation of organisms is the presumed method samples are preferred. Serum is stable for using the same methodology is necessary for
of transmission. Clinical presentation depends on up to 48 hours if stored at 2°C-8°C. Freeze serial titer interpretation.
the size of the inoculum, virulence of the strain, (non–frost-free freezer to avoid defrost cycles)
and host defenses. Nasal or pulmonary infections for longer sample storage. CSF, 1 mL, col- AUTHOR: Erin N. Burton, DVM, MS
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
are most common, but dissemination to the lected in a sterile tube with no additives;
central nervous system (CNS), eyes, skin, bones, process immediately or freeze.
and lymph nodes also occurs. The organism’s • CSF is preferred if CNS signs are present;
variably thick, polysaccharide capsule inhibits may be more sensitive.
phagocytosis; thus degree of inflammation
observed on cytology or histopathology can vary.
Reference Interval
Initial screening done on undiluted samples;
positive serum or CSF usually titered to
endpoint values. Positive titer values vary by
reference laboratory.
Causes of Abnormally High Levels
Latex agglutination test (LAT) for cryptococcal
polysaccharide capsular antigen is widely avail-
able in most reference laboratories. Sensitivity
and specificity of these assays is approximately
90%; however, false-positives can occur.
Next Diagnostic Steps to Consider
if Levels are High
Histopathologic evaluation, cytologic diagnosis, Laboratory Tests
or culture may be helpful to confirm and is
recommended with low titers (typically <200). CRYPTOCOCCUS ANTIGEN TESTING. Modified Wright Giemsa at 100x objective. Cytologic specimens
See p. 223. from a nasal mass in a cat with Cryptococcus sp. suspected Cryptococcus neoformans.

Crystals, Urine Sediment

Definition (e.g., bilirubin, uric acid, cystine) more com- • Calcium oxalate monohydrate and dihydrate:
Precipitation of urinary solutes monly crystallize in acidic urine. Decreased ethylene glycol toxicosis, hyperoxaluria/
urine flow and temperatures (refrigeration) can calciuria
Synonyms promote crystal formation. • Cystine: inherited defect of urinary cystine
Crystalluria transport (cystinuria)
Reference Interval
Physiology • Reported as the number of specific crystals Next Diagnostic Steps to Consider
Urinary crystal formation depends on several per 40x microscopic field objective if Levels are High
factors, including the concentration of • Some crystals can be observed in the urine Review signalment, diet, and medication
urinary solutes, urine pH, urinary flow rate, of healthy dogs and cats (see below). history. Evaluate for hepatic failure or acute
temperature, and storage. Supersaturation of kidney injury. Perform urine culture and
urinary solutes is influenced by hydration Causes of Abnormally High Levels sensitivity if indicated (e.g., struvite crystalluria).
status, diet, and medications. Urine pH and • Struvite, calcium oxalate dihydrate, and
solubility factors are helpful tools in identify- brushite: healthy dog or cat, urolithiasis Important Interspecies Differences
ing crystals. Inorganic salts (e.g., phosphate, • Ammonium biurate and uric acid: porto- Ammonium biurate crystals may be found in
ammonium, magnesium) are less soluble in systemic shunt, hepatic dysfunction healthy Dalmatians and English bulldogs.
neutral or alkaline pH, while organic solutes • Bilirubin: healthy dog, bilirubinuria

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