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Methemoglobinemia, Methemoglobinuria MiraVista Fungal Testing 1365

Pearls be compared directly. Selection of a single high-grade tumors, the mast cell tumor
• The prognostic value of a panel of stains laboratory is recommended, and a compre- panels have limited utility in MCTs that
VetBooks.ir • Several laboratories offer various mast cell • Other than c-KIT PCR to identify potential AUTHOR: Sharon M. Dial, DVM, PhD, DACVP
are clearly low grade or high grade.
hensive interpretation from a board-certified
exceeds the prognostic value of any individual
pathologist should be provided.
stain.
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
tumor panels, the results of which cannot
response to tyrosine kinase inhibitors in

Methemoglobinemia, Methemoglobinuria

Definition (nitrite, copper), drugs (e.g., acetaminophen, tube]) should be refrigerated and sent chilled
Methemoglobin (MetHb) has an iron moiety benzocaine, phenazopyridine, zinc), or plants (not frozen) with assay done the same day
3+
that has been oxidized to the ferric (Fe ) specimen collected. One or more samples
2+
state from the normal ferrous (Fe ) state Next Diagnostic Steps to Consider collected from normal animals submitted
in hemoglobin. if Levels are High as control. Not offered by most veterinary
Methemoglobinemia: accumulation of MetHb • If spot test is positive, consider co-oximetry reference labs; may be run in human lab
in blood to measure concentrations of MetHb if erythrocyte lysing agent does not cause
Methemoglobinuria: presence of MetHb in as a percentage of the total hemoglobin MetHb formation
urine concentration in the blood sample. Arte-
rial blood gas to measure oxygen tension; Relative Cost: Check with local human
Synonym pulse oximetry not reliable but will be low reference lab/hospital ($-$$).
MetHb in methemoglobinemia
• CBC with smear review to determine if Pearls
Physiology hemolytic anemia is present, because it is • Severe methemoglobinemia produces
Increased production of MetHb results from a common sequela to oxidant injury of chocolate-brown discoloration of the blood.
exposure to oxidant chemicals, drugs, plants, erythrocytes • Spot testing is rapid, inexpensive, and may
or decreased reduction of MetHb due to a • Evaluation of red blood cell morphology for be done in-house.
hereditary enzyme deficiency. MetHb cannot Heinz bodies and eccentrocytes (hallmarks • Most chemicals producing methemoglobin-
bind and carry oxygen to tissue. of oxidant injury) emia also produce Heinz body hemolytic
• MetHb reductase determination or genetic anemia.
Reference Interval testing if hereditary deficiency is suspected • “Saturation gap” occurs when there is a dif-
MetHb spot test: drop of venous blood on a ference between SpO 2 and PaO 2 in animals
white paper towel normally is bright red; if Specimen Collection and Handling with methemoglobinemia.
methemoglobin concentration is > 10%, spot Anticoagulated whole blood for spot test; • Methemoglobinemia may cause cyanosis in
remains dark with a brown tinge. Actual value 0.5 mL minimum animals without respiratory distress. Laboratory Tests
measured with co-oximetry; normally represents Co-oximetry on fresh whole blood on ice may
< 2% of total hemoglobin in blood/urine be run at nearby human lab/hospital within AUTHOR & EDITOR: Lois Roth-Johnson, DVM, PhD,
DACVP
2 hours
Causes of Abnormally High Levels MetHb reductase determination: prior arrange-
Hereditary deficiency of methemoglobin ments must be made with a laboratory.
reductase or exposure to oxidant chemicals Whole blood (1 mL in EDTA [lavender top

MiraVista Fungal Testing

Definition body cavity fluids, specifically serum, urine, value and laboratory-supplied suggested
MiraVista is a reference laboratory headquartered CSF, and bronchoalveolar lavage (BAL) fluid. interpretation
in Indianapolis, IN, that specializes in tests that Current tests offered include Aspergillus spp,
identify fungal antigen in body fluids. Some of Blastomycosis dermatitidis, Coccidioides spp, Causes of Abnormally High Levels
these tests offer significant advantages to other Cryptococcus neoformans, Histoplasmosis capsu- Fungal infection, usually systemic or
serodiagnostic methods of mycotic infection. latum. Of these, galactomannan antigen assays invasive
offer an advantage over other serodiagnostics
Synonym for systemic aspergillosis, blastomycosis, and Next Diagnostic Steps to Consider
Fungal antigen tests histoplasmosis. There is considerable cross- if Levels are High
reactivity between the dimorphic fungi. See pp. 81, 121, 184, 223, and 476.
Physiology
During invasive systemic/disseminated fungal Reference Interval Drug Effects
disease, fungal agents can shed specific structural Depends on specific test; may be reported Aspergillus antigen test: piperacillin-tazobactam,
antigens (e.g., cell wall galactomannan) into as positive or negative, or with numerical amoxicillin/clavulanic acid, and fluids containing

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