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1322 Casts, Urine Sediment

(negative/positive +/- strain identification as 2a, Causes of Abnormally Low Levels Lab Artifacts
b or c) RT-PCR (negative or positive result) • Negative fecal ELISA indicates uninfected, Severe hemolysis and lipemia interfere with IFA.
VetBooks.ir Causes of Abnormally High Levels shedding (shedding decreases by 8-12 days Specimen Collection and Handling
very early postexposure, or end of viral
ELISA: rectal swab for in-clinic test per kit
post-natural infection and/or 5-7 days after
• Positive fecal ELISA test indicates viral
onset of clinical signs).
antigen shedding due to natural infection
tainer stored for ≤24 hours (2°-8°C) or longer
(usually strong positive) or recent (4-8 • False-negative fecal ELISA may occur if instructions; 3-5 g fresh feces in plastic con-
days) vaccination with modified live vaccine sample not freshly collected or if viral antigen if frozen. HI, IFA: 1 mL serum (red top tube),
(usually weak positive); one study showed is bound to antibody. can be stored at 2°C-8°C up to 4 days. PCR/
no vaccine cross-reactivity with the SNAP ® • False-negative PCR possible from degradation RT-PCR: fecal swab (minimum 1 g) or 5 g
Parvo ELISA. of nucleic acids via improper sample handling of feces in sterile container; stable for 10 days
• Positive fecal PCR indicates natural infection and storage. at 2°-8°C.
or recent vaccination (for at least 2 weeks • Negative serologic result indicates lack of
postvaccination). Quantitative RT-PCR test exposure to virus, early infection before Relative Cost: $ (fecal antigen ELISA), $$
assists in differentiating vaccine and wildtype seroconversion, or inadequate vaccine (serology, PCR/RT-PCR)
virus by incorporating a technical cut-off to protection.
prevent reporting of positives at the low levels Pearls
seen in vaccinated dogs. Positive serum IgM Next Diagnostic Steps to Consider • In-clinic ELISA and PCR tests are most often
by IFA indicates recent exposure (natural or if Levels are Low used to confirm clinical diagnosis.
vaccination); usually positive by the time If clinical signs and laboratory findings are • Some ELISA tests for canine parvovirus also
clinical signs are present. consistent, but initial test negative, repeat detect feline parvovirus (panleukopenia) from
• Positive IgG titer by IFA indicates exposure test, alternative test or electron microscopic cats that are shedding virus.
(natural or vaccination); can demonstrate evaluation of feces (expensive, not always readily • Laboratory-based HI is necessary for assess-
rising titer in acute and 10- to 14-day available). Histopathologic evaluation and tissue ment of likely protective antibody (sometimes
convalescent serum samples. culture can provide definitive diagnosis, but used in lieu of revaccination).
• Serum antibody titer by HI of ≥ 1:64 require biopsy.
indicates previous exposure (natural or AUTHOR: Patty J. Ewing, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
vaccination) and protective antibody. Drug Effects
Recent vaccination may cause weak positive
Next Diagnostic Steps to Consider ELISA or positive PCR result.
if Levels are High
Positive fecal ELISA or PCR with appropriate
clinical signs is generally diagnostic.

Casts, Urine Sediment

Definition degeneration within the renal tubular lumen, Next Diagnostic Steps to Consider
Cylindrical aggregates of mucoprotein with or resulting in coarsely granular, finely granular, to if Levels are High
without cells that form in the lumen of the waxy casts. As waxy casts require urinary stasis Rule out nephrotoxicity; review history for
renal tubules. for formation, their presence often signifies exposure to nephrotoxin; serum chemistry
oliguric renal failure. White blood cell and profile; renal imaging +/- renal biopsy if
Synonyms red blood cell casts indicate inflammation and indicated clinically
Cylindruria hemorrhage, respectively.
Lab Artifacts
Physiology Reference Interval Dissolution and false-negative results can occur
The formation of casts is initiated by excess • 1-2 hyaline and 0-1 granular casts per low- with delayed processing or dilute or alkaline
precipitated mucoprotein (Tamm-Horsfall power field can be observed in concentrated urine.
mucoprotein), which is normally secreted in urine of clinically normal dogs and cats.
small quantities by the renal tubular epithelial • Cellular and waxy casts are pathologic. Specimen Collection and Handling
cells. Highly concentrated and acidic urine, Process or refrigerate urine within 30 minutes.
decreased urine flow, and excessive serum Causes of Abnormally High Levels
protein promote the precipitation of muco- • Hyaline casts: prerenal or renal proteinuria Relative Cost: $ (as part of urinalysis)
protein. Hyaline casts are pure precipitates of • Cellular and granular casts: acute renal
mucoprotein. When sloughed renal tubular tubular injury (necrosis, nephrotoxicity, or AUTHOR: Shannon D. Dehghanpir, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
epithelial cells become entrapped within the ischemia)
mucoprotein matrix, cellular casts result. These • Waxy casts: persistent tubular injury, typically
cellular (or fatty) casts undergo degrees of in patients with decreased urine output

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