Sample Collection and Handling
Perform venipuncture using the proper technique. For chemistry profiles, collect blood into a clot tube—a serum-separator tube (SST) is recommended.
- Mix SST tube by gentle inversion to distribute the clot activator throughout the sample immediately following collection. Red top tubes without an activator do not require mixing.
- Allow specimen to clot.
- Centrifuge at 3,000 x g for 10 minutes.
- Separate serum from cells as soon as possible following collection. Transfer serum to a separate tube for shipping. Nonbreakable tubes are recommended to prevent damage during transit. Removal and submission of serum from SST tubes is recommended because the barrier can break down in transit.
- Label tube with the animal’s name, owner’s name, and collection date.
- Keep serum refrigerated until shipping.
- Ship on an ice pack.
When submitting canine and feline samples for bile acid analysis, collect both fasting and 2 hr post-prandial specimens into a clot tube—serum separator tubes (SST) are recommended. Additional information about bile acid interpretation can be found in a previous newsletter article.
- Collect a 12 hour fasting sample.
- Collect a 2 hour post-prandial sample (we cannot provide reference intervals if the post-prandial sample is collected at any time other than 2 hours after feeding).
- Allow specimens to clot.
- Centrifuge at 3,000 x g for 10 minutes.
- Separate serum from cells as soon as possible following collection.
- Label all tubes with the animal’s name, owner’s name, and collection date. Also include fasting or 2 hour post-prandial on the appropriate tube.
- Ship on a cold pack.
For other chemistry assays performed by the MSU VDL Clinical Pathology Laboratory, specimen requirements, or submittal procedures please see our catalog of available tests or contact the laboratory.
Calculated Chemistry Tests
Beckman Coulter AU680
- Globulins = Total Protein - Albumin
- Indirect Bilirubin = Total Bilirubin - Direct Bilirubin
- Serum Osmolarity (mmol/L) = (2.0 x [Na+]) + ([Glucose]/18.0) + ([UN]/2.8)
- Anion Gap = ([Na+]+ [K+]) - ([Cl-] + [HCO3-])
- Urine Total Protein:Creatinine ratio = [Micro Total Protein]/[Urine Creatinine]
- GGT:Creatinine ratio = GGT activity/[Urine Creatinine]
- % Fractional Clearance = ([analyte urine]/[analyte serum]) x ([creatinine serum]/[creatinine urine]) x 100
- Na:K ratio = [Na+]/[K+]
- Osmolarity (mmol/L) = (1.86 x Na+) + ([Glucose]/18) + ([UN]/2.8) + 9
- Anion Gap = ([Na+] + [K+]) - ([Cl-] + [HCO3-])
- Calculations for other results are available upon request
Ensuring Accurate Chemistry Results
- Leaving serum or plasma on cells causes artifacts in chemistry results. Glucose will be utilized by cells, resulting in an artifactual hypoglycemia. Cells will leak contents including electrolytes and enzymes. To avoid these problems, serum should be separated from cells as soon as possible following collection.
- SDH (ID) (iditol dehydrogenase) is a relatively labile enzyme. Activity may decrease in samples during routine shipping. Results should be interpreted accordingly.
- Chemistry values can be affected by hemolysis, hyperbilirubinemia, and lipemia. The effect of these substances is indicated in the table below.
- Lipemic samples are cleared by ultracentrifugation for an additional charge if the lipemia is marked and likely to affect results. When possible, animals should be fasted for at least 12 hours prior to blood collection to help avoid lipemia.
Hemolysis can occur in vivo or in vitro. In vitro hemolysis can be avoided by proper blood collection and handling. Tips for sample handling can be found in a previous newsletter article. The laboratory will notify you if the submitted sample is too hemolyzed to analyze. The effect of hemolysis on chemistry tests depends upon the substance being measured. Hemolysis interferes with results by:
- Color interference
- Release of substances that are in higher concentration in cells than in serum or plasma (e.g. the psuedohyperkalemia that occurs in hemolyzed samples from animals, such as horses, with high K-containing erythrocytes).
- Release of substances that interfere with the test method.
This table shows the percentage of change expected with various degrees of hemolysis, lipemia, or icterus. The degree of each interference is noted on a 4-plus scale.