Page 2632 - Cote clinical veterinary advisor dogs and cats 4th

1342 Feline Leukemia Virus (FeLV) Testing Fibrin or Fibrinogen Degradation Products (FDP)

Feline Leukemia Virus (FeLV) Testing
VetBooks.ir Definition

tion, and false-negative results may be due
latent. Negative ELISA with positive IFA
Feline leukemia virus (FeLV) is a gamma- early infection that may persist or become results may be due to specimen contamina-
retrovirus of cats that causes hematopoietic suggests false result, and both tests should to degradation of nucleic acids via improper
neoplasia, immunosuppression, and/or anemia. be repeated, or perform RT-PCR. Positive sample handling and storage or aged sample.
ELISA with negative RT-PCR suggests viral
Physiology nucleic acid below limit of detection, an Specimen Collection and Handling
Following oronasal exposure to FeLV, the virus uncommon strain not detected by PCR, or ELISA: 1 mL serum (red top tube) or EDTA
replicates in oropharyngeal lymphoid tissue. falsely positive ELISA. plasma (lavender top tube). Stable for 7 days
The virus may be cleared with an effective at 2°C-8°C or months if frozen. Performed as
immune response (abortive infection). An inef- Next Diagnostic Steps to Consider in-clinic test kit, or mail out. IFA: 1 mL EDTA
fective immune response results in viremia and if Levels are High plasma (lavender top tube), buffy coat smear, or
replication in bone marrow and lymphoid cells. If ELISA screening test is positive, repeat ELISA unstained, unfixed bone marrow smear. Stable
Infected cats may be transiently viremic with in 6-8 weeks or confirm with IFA test or PCR/ for 48 hours at 2°C-8°C (whole blood); store
latent virus residing in the marrow (regressive RT-PCR. slides at room temperature. PCR: 2 mL EDTA
infection), or may become persistently viremic whole blood (lavender top tube); stable for 10
(progressive infection). ELISAs and other Causes of Abnormally Low Levels days at 2°-8°C; fresh tissue 24 hours at 2°C-8°C
immunochromatographic assays become posi- A negative ELISA or IFA may be present with or frozen for longer.
tive during the primary viremic phase, before either early infection or regressive infection, or
bone marrow infection. See p. 329. in uninfected cats. Relative Cost: $ (ELISA), $$ (IFA, PCR/
RT-PCR)
Reference Interval Next Diagnostic Steps to Consider
ELISA, IFA, and PCR/RT-PCR: reported as if Levels are Low Pearls
positive or negative If the cat was recently exposed to an FeLV- • Vaccination for FeLV involves a different
positive cat but the ELISA is negative, retesting component of the virus than the one detected
Causes of Abnormally High Levels in 30-90 days is recommended. PCR for by ELISA, IFA, or PCR. Therefore, prior
• ELISA (screening test) detects the free soluble proviral DNA may be indicated if latent FeLV vaccination does not affect test results.
FeLV core antigen p27 as early as 30 days infection is suspected or for potential blood • ELISA test is more sensitive (more likely
after infection; a positive ELISA indicates donors. If positive ELISA and negative IFA, to catch all FeLV-positive cases) compared
viremia, but viremia may be transient. False- repeat both tests in 6-8 weeks. PCR/RT-PCR to IFA, but less specific (may erroneously
positives occur infrequently (usually due to can also be performed. identify a few FeLV negative cats as positive,
technical error; sensitivity = 90%-98%; especially in populations with low prevalence
specificity = 98%-99%). IFA (confirma- Lab Artifacts of FeLV).
tory test) detects the cell-associated FeLV Hemolysis or lipemia may cause a false-positive • Only highly reliable laboratories should
core antigen p27 as early as 6 weeks after or false-negative ELISA result. Marked be entrusted with FeLV PCR testing; they
infection; a positive IFA indicates persistent thrombocytopenia or neutropenia may cause should provide information on reliability of
bone marrow infection. a false-negative IFA. Use of excessively thick testing.
• Discordant results are possible. Positive buffy coat or bone marrow smears may cause
ELISA with negative IFA is suggestive of a false-positive IFA test. False-positive RT-PCR AUTHOR: Patty J. Ewing, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP

Fibrin or Fibrinogen Degradation Products (FDP)

Definition fibrinogen for active sites on thrombin and Causes of Abnormally High Levels
Fibrin or fibrinogen degradation products interfering with the conversion of fibrinogen • Increased fibrinolysis: internal hemorrhage,
(FDPs) are protein fragments of fibrin or to fibrin. thromboembolism, DIC, sepsis, hyperadre-
fibrinogen that have been cleaved by plasmin • FDPs interfere with platelet aggregation by nocorticism, protein-losing nephropathy or
as part of fibrinolysis. Assays to detect FDPs binding to the fibrinogen binding site on enteropathy, pancreatitis, parvoviral infection
are used for identifying increased fibrin or platelets. (dogs)
fibrinogen breakdown that is seen with exces- • FDPs are eliminated by the liver and kidney. • Increased fibrinogenolysis: rattlesnake
sive coagulation (disseminated intravascular Patients with hepatic or renal disease can have envenomation
coagulation [DIC]). Plasmin can act on both increased FDPs in the absence of significant • Decreased FDP clearance: hepatic disease,
fibrinogen and fibrin. Assays for FDPs do fibrin(ogen)olysis. kidney disease
not differentiate between fibrinolysis and
fibrinogenolysis. Reference Interval Next Diagnostic Steps to Consider
Semiquantitative normal values: dogs, if Levels are High
Physiology 0-10 mcg/mL; cats, 0-8 mcg/mL. Abnormal • CBC with platelet count, serum biochemistry
• Plasmin breaks down fibrin and fibrinogen values are reported as moderately increased or profile, urinalysis
into Fragments D and E (FDPs). FDPs markedly increased. • Coagulation profile: activated partial
inhibit coagulation by competing with thromboplastin time, prothrombin time,

www.ExpertConsult.com