The Minimum Diagnostic Database: Chemistry

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1 The Minimum Diagnostic Database: Chemistry Jeff Niziolek, DVM Professional Services Veterinarian IDEXX Laboratories, Inc. 208 Bay Meadows Drive Holland, MI Biochemical profiling is a wide and important part of veterinary testing. Animals can t talk, so how do you know what s going on with them? Both dogs and cats are not often motivated to tell us about ailments or diseases that may be affecting them, and they are often excellent at hiding their symptoms. Performing a chemistry profile can help uncover some of those abnormalities. Chemistry testing evaluates overall animal health and organ function while assisting clinicians in identifying disease processes, monitoring progression of changes, and is also important in establishing baseline values in normal patients. It is valuable to consider a chemistry not only with sick patients, but for scenarios including pre-anesthesia, preventive care or wellness, and therapeutic drug monitoring. Blood chemistry and electrolytes give us insights into the function of the: Liver Kidney Adrenal glands Pancreas Blood Sugar Hydration status Acid-base Electrolyte and mineral disorders i.e. calcium. While the biochemical profile provides a lot of information, it is important to ensure that the information is sorted, grouped, and then evaluated properly to gain a clear and objective perspective. By organizing and evaluating the data in a body systems approach, it can be much easier to interpret the results. Here is a body system approach to organizing the information in the profile: Total Body/acid base: GLU, TP, ALB/Electrolytes (Na, Cl, K, Ca, TCO 2 ) Primary tests include: GLU Glucose is the basic energy source for the body. TP Total protein in the blood is primarily composed of albumin and globulins with a minor contribution from coagulation proteins and fibrinogen. ALB Albumin is an important regulator of osmotic equilibrium in the body and is also a carrier for highly protein-bound substances (e.g. calcium, thyroxine, fatty acids, and some drugs). It is produced in the liver. Na Sodium is the most abundant cation in the extracellular fluid. It is partially responsible for the regulation of fluid volume within the blood stream. Sodium also is important for nerve and muscle function. Cl Chloride is the most abundant anion in the extracellular fluid. Chloride is important for acid/base balance, cellular fluid transport, and nerve function.

2 K Potassium is an intracellular ion that is responsible for maintenance of fluid and electrolyte balance. Potassium is essential for muscle and nerve function. Ca Calcium is an ion that is required by the body for numerous intracellular and extracellular functions. Calcium also is a major component in the structure of bone. TCO 2 TCO 2 (Bicarbonate) acts an important buffer in the blood and is used to evaluate acidbase status. Liver Panel: Primary tests include: ALT Alanine Aminotransferase is a cellular enzyme released in response to injury of liver cells. ALT can also increase mildly with muscular injury and gastrointestinal disease. ALP Alkaline Phosphatase is primarily an indicator of cholestatic liver disease. It also increases with severe bone destruction and due to steroid induction. AST Aspartate Aminotransferase is a cellular enzyme that primarily increases due to liver and muscle damage. GGT Gamma Glutamyl Transferase is a marker of cholestatic liver disease. TBIL Bilirubin is an indicator of liver disease, gall bladder disease or hemolysis. CHOL Cholesterol is one of the main lipids in the body. It has an important role as a component of cell membranes. Secondary tests include: BUN Blood Urea Nitrogen is produced in the liver and excreted by the kidneys. It is a marker for both liver and kidney dysfunction. GLU ALB GLOB Globulins are produced in the liver and by the cells of the immune system (gamma globulins). They have many vital roles in the body including maintenance of osmotic balance, immune system function, and the inflammatory response. TRIG Triglycerides are lipid compounds that are a vital energy source for cells. Kidney Panel: SDMA (currently included on all panels at IDEXX Reference Laboratories, and available on Catalyst as of December 2016) IDEXX SDMA Test is a more reliable indicator of kidney function than creatinine because SDMA detects declining kidney function earlier and is not impacted by muscle mass. Creatinine can miss early function loss and be falsely decreased in patients with reduced muscle mass. SDMA increases in acute and active injury as well as chronic kidney disease. When SDMA is increased, action should be taken. BUN CREA Creatinine is a breakdown product of muscle. It is removed by the kidneys and is an indicator of renal function. BUN/CREA Ratio PHOS Phosphorus is essential for energy production, protein synthesis, and acid/base balance in the body. Phosphorus is also a major component of bone. Exocrine Pancreas Panel:

3 AMYL Amylase is an enzyme produced primarily in the pancreas to digest dietary carbohydrates in the intestine. LIPA Lipase is an enzyme produced primarily in the pancreas to break down dietary fats in the small intestine. A total body amylase and lipase have value as part of a minimum database. Elevated amylase and/or lipase results are indicative that something could be wrong with the patient. It could be the pancreas, the liver, or some other lipase producing organ. To rule out the pancreas as the culprit, veterinarians should run a cpl/fpl test. These tests are considered to be more valuable in dogs than in cats. In cats, serum amylase activity is variable in patients with pancreatitis and can be decreased (experimental cases), within reference intervals, or mildly increased. Also, in cats with pancreatitis, serum lipase is usually increased, but can also be within reference intervals Samples Unlike a CBC which is run on whole blood, the chemistry parameters are read from either a serum or plasma sample. Serum is the fluid portion of blood after it has been allowed to clot and centrifuged. It contains all electrolytes, antibodies, and hormones, but no longer has the clotting factors or fibrinogen. To obtain serum, whole blood samples should be allowed to clot for 20 minutes before spinning to minimize fibrinogen in the spun sample. Serum sample containers: Serum tube and microtainer No anticoagulant. May be untreated or treated with clot activator to assist in clotting. May contain gel. Greiner brand is red top with black tube. Others often just red. Greiner microtainer is yellow. Serum separator tube No anticoagulant. Contains a gel separator that allows the serum to be cleanly separated from the red cell clot when spun. Greiner brand is red top (with yellow). Others marble or tiger top. Chemistry profiles can also be run on plasma. When chemicals (anticoagulants) are introduced to a whole blood sample to prevent clotting, the fluid left over after centrifugation is called plasma. Plasma contains the protein fibrinogen, which is missing from serum because it has been converted into the soluble fibrin clot. Plasma sample containers: Green top tube, microtainer, and Catalyst whole blood separator Sodium heparin or lithium heparin anticoagulant. When using green top tubes, it is important to know which anticoagulant is being used, as different chemistries/analytes may not be supported with one type or the other. In general, serum or plasma should be analyzed within 4 hours. Serum/Plasma should be removed from the clot/cells immediately after spinning and stored in an untreated tube. After 4 hours, store

4 serum/plasma in the refrigerator 2-8ºC (36-46ºF) for up to 48 hours. After 48 hours, freeze serum/plasma -18ºC. Interfering substances Interfering substances can affect the ability for a chemistry analyzer to accurately measure results. There are 3 main types of interfering substances: Hemolysis Lipemia Icterus Hemolysis produces a reddish hue, varying from pale pink to deep red because of damage to red cells during sample preparation or intravascular hemolysis (hemoglobin). To minimize hemolysis: Choose the appropriate needle size for the patient. Common size for kittens and small puppies is 25G (gauge) Common size for cats and small to medium sized dogs is 22G Common size for medium to large size dogs is 20G Related: A three-part (or sampling) syringe usually makes for a smoother draw. Three-part syringes have a silicon-lubricated part on the plunger. (You might be using a two-part (or injection) syringe.) Draw the sample slowly and evenly, creating just enough force for the syringe to fill. Pulling back on the syringe plunger can cause a strong vacuum effect and lyse (burst) red cells, causing hemolysis. When filling a vacutainer tube, allow the vacuum to pull in the sample instead of depressing the plunger on the syringe. Forcing the sample thru the needle can cause red cells to lyse. When transferring a sample to a non-vacutainer tube, remove the needle from the syringe before dispensing. When filling an anticoagulant tube (heparin, EDTA, etc), be sure to fill the tube with the manufacturer recommended volume (typically at least ¾ full) and invert the tube 3 to 4 times to allow the anticoagulant to mix thoroughly with the sample. Keep the patient calm if possible. Stress can make blood draw difficult increasing a likelihood of hemolysis Lipemia produces a pale, milky appearance, possible floating fat globules due to recent ingestion of a fatty meal or abnormal lipid metabolism. To minimize lipemia: Fasting the patient for hours can help reduce or eliminate lipemia. Perform the flash freeze technique. Place the serum or plasma sample in the refrigerator for 20 minutes, scoop lipids off the top using the stick end of a cotton-tipped applicator. Re-spin the sample and allow to acclimate at room temperature before running. NOTE: Some patients (such as Schnauzers) may have a naturally fatty sample due to issues with metabolism and no amount of fasting will limit lipemia

5 Icterus results in a transparent yellow to opaque brown discoloration as a result of obstructive or biliary disease, intravascular hemolysis. This cannot be minimized because icterus is part of a disease process References Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 6th ed. St. Louis, MO: Elseveier Saunders; Latimer KS, Mahaffey EA, Prasse KW, eds. Duncan and Prasse's Veterinary Laboratory Medicine: Clinical Pathology, 4th ed. Ames, IA: Blackwell; Stockham SL, Scott MA. Fundamentals of Veterinary Clinical Pathology, 2nd ed. Ames, IA: Blackwell; Willard MD, Tvedten H, eds. Small Animal Clinical Diagnosis by Laboratory Methods, 4th ed. St. Louis, MO: Saunders; Braff J, Aguiar J, Yerramilli M, et al. Analysis of Serum Symmetric Dimethylarginine Concentration in Patient Samples Identified Through Retrospective Trending of Serum Creatinine. [ACVIM Abstract U-43] J Vet Intern Med. 2014; 28(3): Braff J, Obare E, Yerramilli M, et al. Relationship Between Serum Symmetric Dimethylarginine Concentration and Glomerular Filtration Rate in Cats. J Vet Intern Med. 2014, Vol 28: Hall JA, Yerramilli M, Obare E, et al. Comparison of Serum Concentrations of Symmetric Dimethylarginine and Creatinine as Kidney Function Biomarkers in Cats with Chronic Kidney Disease. J Vet Intern Med. 2014; 28: Hall JA, Yerramilli M, Obare E, Yerramilli M, Almes K, Jewell DE. "Serum Concentrations of Symmetric Dimethylarginine and Creatinine in Dogs with Naturally-Occurring Chronic Kidney Disease." J Vet Intern Med. 2016; 30(3): Hall JA, Yerramilli M, Obare E, et al. "Relationship Between Lean Body Mass and Serum Renal Biomarkers in Healthy Dogs." J Vet Intern Med. 2015; 29(3): Nabity MB, Lees GE, Boggess M, et al. "Symmetric Dimethylarginine Assay Validation, Stability, and Evaluation as a Marker for Early Detection of Chronic Kidney Disease in Dogs." J Vet Intern Med. 2015; 29(4): Nabity MB, Lees GE, Boggess M, et al. Week to Week Variability of Iohexol Clearance, Serum Creatinine, and Symmetric Dimethylarginine in Dogs with Stable Chronic Renal Disease. [ACVIM Abstract NU-14]. J Vet Intern Med. 2013; 27(3): 734. Nabity MB, Lees GE, Boggess M, et al. "Symmetric Dimethylarginine Assay Validation, Stability, and Evaluation as a Marker for the Early Detection of Chronic Kidney Disease." J Vet Intern Med. 2015; 29(4): Prusevich P, Patch D, Obare E, et al. "Validation of a Novel High Throughput Immunoassay for the Quantitation of Symmetric dimethylarginine (SDMA)" [AACC Abstract B-048]. Clin Chem. 2015; 61(S10):S135. Rentko V, Nabity M, Yerramilli M, et al. Determination of Serum Symmetric Dimethylarginine Reference Limit in Clinically Healthy Dogs. [ACVIM Abstract P-7]. J Vet Intern Med. 2013; 27(3): 750.