L

L



Lactate



DEFINITION


Metabolic end product of anaerobic glycolysis



SYNONYM


Lactic acid



TYPICAL NORMAL RANGE


Range: 1.8-22.5 mg/dL; <2 mEq/L (experimental studies, primarily in dogs at rest). Unit conversion: mg/dL × 0.112 = mEq/L; 1 mmol/L = 1 mEq/L.



PHYSIOLOGY


Normally produced in small quantities in skin, erythrocytes, brain, skeletal muscle, GI tract. Increased production occurs when tissues (primarily skeletal muscle and GI tract) must maintain energy production under anaerobic conditions (tissue hypoxia). Abnormal carbohydrate metabolism associated with some diseases may also increase production. Liver and kidney are the primary consumers of lactate. Lactic acidosis occurs when production exceeds utilization.



CLINICAL APPLICATIONS



CAUSES OF ABNORMALLY HIGH LEVELS



• Hypoxemic: strenuous exercise, seizures, any cause of decreased oxygen availability (shock, hypovolemia, cardiac disease, pulmonary edema)

• Nonhypoxemic: gastric dilatation/volvulus, diabetes mellitus, liver failure, neoplasia, sepsis, renal failure, hypoglycemia, babesiosis, rare hereditary defects (mitochondrial myopathy, pyruvate dehydrogenase deficiency)


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH



• Not measured as part of routine biochemical profile, but cageside use is increasingly common in emergency/critical care setting.

• Lactic acidosis should be suspected when there is an unexplained increase in the anion gap. Evaluate patient for underlying causes.


SPECIMEN AND PROCESSING CONSIDERATIONS


DRUG EFFECTS ON LEVELS: Increases associated with salicylates, ethylene glycol, epinephrine, and phenobarbital


LAB ARTIFACTS THAT MAY INTERFERE: Increased: delayed plasma harvest, venous stasis (prolonged holding off of the vein), struggling during venipuncture. Decreased: free hemoglobin, bromide (method dependent).


SPECIMEN: Plasma collected in lithium heparin (green-top tube) or sodium fluoride (grey-top tube); must be centrifuged immediately and plasma removed from erythrocytes. Refrigerate immediately or freeze. Some blood gas analyzers use whole blood.


RELATIVE COST: $$$ (at reference laboratory)



PEARLS


Markedly elevated lactate concentrations have been associated with a poor prognosis in critical care settings. For example, dogs with gastric dilatation/volvulus have a 99% survival rate if plasma lactate <6 mmol/L but a 58% survival rate if plasma lactate >6 mmol/L.


AUTHOR: ROBIN W. ALLISON



Lactate Dehydrogenase



DEFINITION


Cytosolic enzyme found in most cells in the body



TYPICAL NORMAL RANGE


Dogs: 50-380 U/L. Cats: 46-350 U/L.



PHYSIOLOGY


Lactate dehydrogenase (LDH) catalyzes the oxidation of L-lactate to pyruvate and the reverse reaction. LDH is nonspecific because it is present in many tissues. It is concentrated in heart, skeletal muscle, liver, kidney, and erythrocytes. Leakage of this enzyme into the blood and extracellular space occurs with injury to most tissues. It also increases with only slight sample hemolysis. There are five LDH isoenzymes that can be separated electrophoretically. These isoenzymes are present in certain tissues and are therefore more specific: one primarily in myocardium, another primarily in skeletal muscle, and the remaining isoenzymes are present in several different tissues. Therefore LDH isoenzyme determination may be used to identify cardiac or skeletal muscle injury. Yet LDH isoenzyme measurement is usually restricted to research applications in veterinary medicine. LDH isoenzyme determination is not practical, readily available, or cost effective in the clinical setting, since there are other more sensitive and specific markers of muscle and hepatic injury.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Cardiac disease, skeletal muscle disease, renal injury, liver disease, and hemolysis


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Evaluate for muscle injury, hepatic disease, or hemolytic anemia.



SPECIMEN AND PROCESSING CONSIDERATIONS


LAB ARTIFACTS THAT MAY INTERFERE: Hemolysis results in false elevation, because red blood cells contain LDH.


SPECIMEN: Serum (red-top tube). Store at 4○C.


RELATIVE COST: $


AUTHOR: RUANNA GOSSETT



Lead, Blood Level



DEFINITION


Lead intoxication is relatively common, and whole-blood lead levels are the diagnostic test of choice. Exposure is usually by ingestion. Inhalation, dermal, subcutaneous/intramuscular exposure occur uncommonly.



TYPICAL TOXIC RANGE



• 0.6 ppm or greater is diagnostic of lead toxicosis.

• 0.35 ppm or greater with signs and confirmatory tests (d-aminolevulinic acid [ALA] or fecal lead) is also diagnostic.


PHYSIOLOGY


Although lead is poorly absorbed from the digestive tract, once absorbed it is retained by tissues (kidney, bone). Blood levels decline slowly; they may be elevated for 1-2 months after a single exposure. Blood concentration indicates exposure but does not reflect exposure duration or total body concentration. Lead crosses the placental barrier and is also excreted in milk. Young animals are more susceptible to toxicosis.


Lead exposure results in increased urinary excretion of ALA and inhibits conversion of coproporphyrinogen III to protoporphyrin and heme synthetase. Interference with hemoglobin synthesis, hemogram abnormalities such as basophilic stippling, and increased number of nucleated red blood cells in nonanemic patients are suggestive but not diagnostic of lead toxicosis.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Exposure to lead


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Serum ALA dehydratase inhibition and erythrocyte protoporphyrin assays are highly sensitive tests for exposure and an indication of possible effect of lead. They are not a substitute for blood lead assay, which confirms the presence of lead. Fecal lead analysis may be of benefit; a value of =35 ppm is suspect.


IMPORTANT INTERSPECIES DIFFERENCES: Lead toxicosis is less common in cats than dogs.



SPECIMEN AND PROCESSING CONSIDERATIONS


SPECIMEN: Heparinized (green-top tube) or EDTA (lavender-top tube) whole blood. Because 90% of circulating lead is bound to erythrocytes, serum lead is not routinely used and not readily interpretable.


RELATIVE COST: $$



PEARLS



• Kidney and liver tissue may be submitted if blood is not available. Kidney is considered preferable (=10 ppm is diagnostic). Formalin-fixed samples may be used for retrospective analyses.

• Chronic exposure is more common than acute exposure.

• Blood levels and clinical signs do not always correlate. Blood levels are the best indicator of lead exposure but may not indicate duration or dose of exposure.

• Ingested items containing lead may be seen radiographically.

AUTHOR: SHERRY J. MORGAN



Left Shift



DEFINITION


The presence of band neutrophils (or earlier neutrophilic precursors such as metamyelocytes or myelocytes) in peripheral blood. This finding nearly always indicates active inflammation. It is clinically useful to define the type of left shift present in leukograms. When segmented neutrophils are also increased, the left shift can be described as “regenerative,” suggesting appropriate marrow response to increased tissue demands for neutrophils. Alternately, when the segmented neutrophil count is unchanged or decreased, the left shift is described as “degenerative,” suggesting the granulopoietic response of marrow is outweighed by tissue demand.



TYPICAL NORMAL RANGE


Dogs: 0-0.3 × 103 band neutrophils/μL. Cats: 0-0.2 × 103 band neutrophils/μL.



PHYSIOLOGY


Band neutrophils, metamyelocytes, and myelocytes are late neutrophilic precursors that normally remain in the marrow storage pool to differentiate into segmented neutrophils. If intense tissue demand for neutrophils during inflammation depletes the segmented neutrophils from the marrow storage pool, band neutrophils (and earlier precursors) can be prematurely released from the marrow into blood.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Acute inflammation, granulocytic leukemia


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Identify source of inflammation; if none is found despite comprehensive evaluation and repeated assessments, a bone marrow aspirate and core biopsy could be indicated to assess for granulocytic leukemia (rare).



SPECIMEN AND PROCESSING CONSIDERATIONS


SPECIMEN: EDTA whole blood (lavender-top tube) and freshly prepared blood smear for laboratory to stain



PEARLS



• Always examine a stained blood smear for band neutrophils, because the neutrophil counts generated by automated hematology analyzers do not distinguish between segmented and band neutrophils. The presence of toxic changes in neutrophils is another indicator of intense inflammation.

• The hyposegmentation of neutrophils in Pelger Huët syndrome is not considered a left shift.

AUTHOR: STEPHEN D. GAUNT



Leptospira Serology, Canine



DEFINITION


Leptospirosis is a zoonotic disease caused by pathogenic serovars of Leptospira interrogans, a motile, spiral-shaped bacterium (spirochete). Serovars of importance include canicola, icterohaemorrhagiae, grippotyphosa, pomona, hardjo, bratislava, and autumnalis.



TYPICAL NORMAL RANGE


Reported as titer values; panel of serovars varies among laboratories.



PHYSIOLOGY


Organisms penetrate abraded skin and/or mucous membranes, replicate within bloodstream; rapid dissemination to multiple organs, most importantly liver and kidney (allows shedding in urine). Organisms replicate in the renal tubular epithelium, causing chronic tubulointerstitial nephritis and persistent carrier state if untreated.


Vaccines elicit immunity against canicola and icterohaemorrhagiae serovars; newer vaccine (Fort Dodge Duramune) elicits immunity against these plus grippotyphosa and pomona.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Microscopic agglutination test (MAT): a titer of =1:800 or fourfold rise in titer (paired serum 3 weeks apart) to a serovar against which the dog has not previously been vaccinated suggests active disease. Vaccine-induced titers are generally low (<1:800) but may be as high as 1:3200; these higher titers generally do not persist longer than 3 months.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: PCR using urine, blood, cerebrospinal fluid, aqueous humor, or tissue is possible, as is direct fluorescent antibody testing on tissue (kidney, liver). Darkfield microscopy or culture (blood, urine) prior to antibiotic therapy can be performed but is technically difficult and not widely available.


CAUSES OF ABNORMALLY LOW LEVELS: Early infection, antibiotic treatment


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: ELISA for immunoglobulin (Ig) G and IgM antileptospiral antibodies. IgM may be detected 1 week after infection. May be useful in detecting acute leptospirosis prior to IgG increase.



SPECIMEN AND PROCESSING CONSIDERATIONS


DRUG EFFECTS ON LEVELS: Antibiotic therapy may cause a decreased MAT titer, prevent a rising titer in paired sample, and cause negative PCR results and negative culture results.


SPECIMEN: Collect 2 mL of serum (red-top tube). Stable for 4 days at 4○C or longer at 0○C.


RELATIVE COST: $$

< div class='tao-gold-member'>

Related posts:

  1. D
  2. Y
  3. G
  4. K

Stay updated, free articles. Join our Telegram channel
Tags:
Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on L

Full access? Get Clinical Tree
Get Clinical Tree app for offline access