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Creatine Kinase (CK) 1329

Causes of Abnormally High Levels including prednisolone, 11-deoxycortisol, Pearls
Hyperadrenocorticism, general illness, or other prednisone, and others. Ketoconazole inhibits • Baseline cortisol concentration can fluctuate
VetBooks.ir Next Diagnostic Steps to Consider are used therapeutically to decrease cortisol • Baseline cortisol > 2 mcg/dL effectively rules
steroid synthesis. Trilostane and mitotane
and so is of limited value.
stressors
out hypoadrenocorticism, but cortisol below
production.
if Levels are High
In a patient with suspected hyperadrenocorti- Lab Artifacts this cut-off warrants confirmatory testing
(generally ACTH stimulation test).
cism, baseline cortisol concentration is of • Do not use serum separator tubes for blood • Urine cortisol to creatinine ratio can be used
limited value. Instead, ACTH stimulation collection; gel from serum separator tubes as a screening test for hyperadrenocorticism;
testing or low-dose dexamethasone suppression can interfere with cortisol measurement. however, diagnosis requires ACTH stimu-
testing should be performed (p. 485). • EDTA contamination and icterus invalidate lation testing or low-dose dexamethasone
results. Multiple assay types available; use a suppression testing.
Causes of Abnormally Low Levels reputable laboratory with validated results
Hypoadrenocorticism, administration of ster- for dogs and cats. AUTHOR: Angela Royal, MS, DVM, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
oids, or treatment with ketoconazole, trilostane,
mitotane Specimen Collection and Handling
Collect blood into plain red top tubes, allow to
Next Diagnostic Steps to Consider clot, centrifuge, and transfer serum to a separate
if Levels are Low tube clearly labeled with the sample ID/time.
If hypoadrenocorticism is suspected, ACTH Ship samples frozen or refrigerated, on ice.
stimulation testing should be performed for
confirmation (p. 512). Relative Cost: Cortisol $$; urine cortisol:
creatinine ratio $$
Drug Effects
Cortisol assays may cross-react with pharma-
cologic steroids administered within 24 hours,

Creatine Kinase (CK)

Definition concentrations indicate ongoing muscle Important Interspecies Differences
Cytosolic enzyme with highest activity in damage. Increased serum CK is common in anorexic
skeletal muscle, cardiac muscle, smooth • CK isoenzymes may be measured to more cats.
muscle, brain, and nerves. Skeletal muscle specifically localize muscle damage to
injury is responsible for clinically significant cardiac or skeletal muscle. CK isoenzyme Lab Artifacts Laboratory Tests
increases in serum concentrations in dogs measurements are not routinely used in • Increase: hemolysis, lipemia, hyperbilirubi-
and cats. veterinary medicine. In human cardiology, nemia, contamination of blood with muscle
other biomarkers have superseded CK (pp. fluid during difficult venipuncture; dilution
Synonym 1369 and 1389). of samples (attributed to dilution of CK
Creatine phosphokinase (CPK) inhibitors in serum)
Reference Interval • Decrease: collection in citrate (blue top tube)
Physiology Dogs: 10-200 U/L; cats: 64-440 U/L or sodium fluoride (gray top tube)
• CK is critical for energy production causing
muscle contraction. Causes of Abnormally High Levels Specimen Collection and Handling
• CK catalyzes the formation of adenosine Trauma, exertion, seizures, malignant hyper- Serum (red top tube), heparinized plasma (green
triphosphate (ATP) by transfer of high- thermia, intramuscular injections, degenerative top tube), or EDTA plasma (lavender top tube).
energy phosphate from creatine phosphate muscle disease, infectious and noninfectious Refrigerated samples are stable for 8-12 hours;
to adenosine diphosphate (ADP). Catalyzes (metabolic, toxic, immune-mediated, nutri- samples stored at −20°C are stable for 2-3 days.
the reverse reaction when muscles are at rest tional) myopathies, muscle ischemia/necrosis
• Serum CK activity is primarily of muscle (e.g., arterial thromboembolism), anorexia in Relative Cost: $
origin, and is a sensitive indicator of skeletal cats resulting in muscle catabolism
muscle damage. Pearls
• CK is released into the interstitium when Next Diagnostic Steps to Consider Persistent exceedingly high CK levels (e.g.,
muscle membranes become damaged. Plasma if Levels are High > 200,000 U/L) are strongly suggestive of
concentration increases 4-6 hours after injury Evaluate for muscle disease or injury, or muscle muscular dystrophy.
and peaks at approximately 12 hours. Values catabolism. In dogs, as in people, serum cardiac
return to normal within 24-48 hours. troponin-I levels are probably more sensitive AUTHOR: Ruanna E. Gossett, DVM, PhD, DACVP
• The half-life in blood is approximately 2-4 and specific for myocardial damage than CK EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
hours. Persistently increased serum CK myocardial isoenzyme.

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