Contributors: Kathleen P Freeman

 Species: Canine   |   Classification: Lab Tests

Overview Sampling Tests Result Data Further Reading


Measuring serum or plasma levels of nutrients, metabolites, enzymes, etc can provide general or specific data about organ function and disease processes. Print-off the owner factsheet on 'Samples - how they help your vet' to give to your client.


In combination

  • Biochemical tests are useful only when combined with clinical data from history and physical examination of the patient.


Source of Test Material

Quantity of Test Material

  • 2 ml serum or plasma. Check with laboratory regarding minimum recommended volume for single test or in combination with other tests.
  • Depends on number of laboratory tests requested.

Sample Collection Technique

Quality Control


  • Hemolysis, lipemia and/or and aging affects the accuracy of many tests.

Timing of test

  • Unless specifically indicated, animals should be fasted overnight before sampling to avoid lipemia - this contributes to inaccurate results.
    Lipemia may make sample useless for some biochemical tests.

Sample storage

  • Refrigerate before dispatch.

Sample transport



  • A number of different methodologies may be available for any given test.


  • Many tests are routinely available - if in doubt, contact the laboratory to confirm availability of a specific test.



  • The ability of a test to produce a positive result in all animals that do have disease.
    A high sensitivity may be associated with a reduction in speicificity as false positive reactions may occur.


  • The ability of a test to produce a positive result only in animals that do have disease.
    A high specificity may be associated with a lower sensitivity as some false negative may occur.

Predictive value

  • Predictive value = how well the test performs in a given population of animals.
  • Influenced by the prevalence of the disease in the population being tested.
  • Positive predictive value is probability of an abnormal test result indicating presence of disease.
  • Negative predictive value is probability of a test result that is within normal limits corresponding to the absence of disease.
  • Predictive value of positive test = p x sensitivity/p x sensitivity + (1-p) x (1-specificity).
  • Predictive value of a negative test = (1-p) x specificity/(1-p) x specificity + P X (1-sensitivity).
  • p = prevalence of disease.


  • In a study of dogs with and without x-disease (diagnosed at necropsy) the following results are obtained:
    • Positive with test: x-disease present 235 (TP), x-disease absent 16 (FP) - total 251.
    • Negative with test: x-disease present 15 (FN), x-disease absent 200 (TN) - total 215.
    • Total: x-disease present 250, total x-disease absent - 216.
  • 1. Sensitivity = TPx100/TP+FN = 235x100/235+15 = 235/250x100 = 94%.
  • 2. Specificity = TN/TN+FPx100 = 200/200+16x100 = 200/216x100 = 93%.
  • It is estimated that x-disease occurs in about 20% of the population that will be tested.
  • 3.Predictive value of a positive test = p(sens)/p(sens) +(1-p)(1-spec) = 0.20(0.94)/20(94)+(0.80)(0.07) = 0.1880/0.1880+0.0560 = 0.1880/0.2440 = 0.77. So you would expect disease in 77 out of every 100 with a positive test.
  • If prevalence is only 2%: PVPT = 0.02(0.94)/0.02(0.94)+(0.80)(0.07) = 0.0188/0.0188+0.0560 = 0.0188/0.0748 = 0.25. So you would expect to have x-disease in only 25 animals out of every 100 with a positive test.
  • 4. Predictive value of a negative test (PVNT) = (1-p)(spec)/(1-p)(spec)+p(1-sens).
  • If prevalence is 20%: (0.80)(0.93)/(0.80)(0.93)+0.20(0.06) = 0.7444/0.744+0.012 = 0.744/0.756 = 0.98. So would expect 98 out of every 100 animals with a negative test to be truly free of x-disease.
  • If prevalence is 2%: (0.98)(0.93)/(0.98)(0.93)+(0.02)(0.06) = 0.9114/0.9114+0.0012 = 0.9114/0.9126 = 0.998. So would expect 99.8 out of every 100 dogs with a negative test to be truly free of x-disease.

Technique (Intrinsic) Limitations

  • In general, results of any given test are most significant when interpreted in conjunction with other laboratory and clinical findings.

Result Data

Normal (Reference) Values

  • Reference intervals are usually established based on statistical determination of values which includes 95% of the population of normal animals.
  • This means that 5% of normal animals have a value outside this range.
  • The more tests that are performed the greater the chance of one of these being outside the normal range in a healthy animal.
    Do not base a clinical diagnosis on one test result.
  • Reference intervals are dependent on test method used.
  • Individual laboratories should supply reference intervals for their tests.
  • Information about numbers and types of animals used for determination of reference intervals and statistical methods used should be available by request.

Errors and Artifacts

  • Poor handling of sample prior to testing particularly:
    • Lipemia (inadequate fasting).
    • Hemolysis (traumatic sampling or prolonged storage).
  • Test inaccurately performed (unlikely in commercial laboratory, more common in practice laboratory).
  • Sample collected into inappropriate transport medium or anticoagulant (see sample tube prefence tableBlood sample tube requirements table 01).
  • Over interpretation of results.
  • Artefactual hemolysis may be caused by:
    • Sampling with wet needle or syringe.
    • Traumatic sample technique, ie excessive suction applied to syringe with small needle.
    • Trauma with shaking sample to mix anticoagulant.
    • Prolonged storage before separation.
    • Centrifugation in an unbalanced centrifuge.

Further Reading


Refereed papers

Other sources of information

  • Kaneko J J, Harvey J W & Brass M L (1997) Eds. Clinical Biochemistry of Domestic Animals. 5th edn. Academic Press, USA.