Canis ISSN: 2398-2942 Blood biochemistry: overview Contributor(s): Kathleen P Freeman Overview Sampling Tests Result Data Overview 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. Parameters measured include: Total protein Blood biochemistry: total protein. Albumin Blood biochemistry: albumin. Total globulin Blood biochemistry: total globulin. Gamma globulins Blood biochemistry: gamma globulin. Sodium Blood biochemistry: sodium. Potassium Blood biochemistry: potassium Chloride Blood biochemistry: chloride. Bicarbonate Blood biochemistry: bicarbonate. Calcium Blood biochemistry: total calcium. Phosphate Blood biochemistry: phosphate. Copper Blood biochemistry: copper. Cobalt. Selenium. Lead. Iron Blood biochemistry: iron. Urea Blood biochemistry: urea. Creatinine Blood biochemistry: creatinine. Ammonia Blood biochemistry: ammonia. Glucose Blood biochemistry: glucose. Fructosamine Blood biochemistry: fructosamine. Bile acids Blood biochemistry: bile acids. Bilirubin - direct Blood biochemistry: direct bilirubin and total Blood biochemistry: total bilirubin. Cholesterol Blood biochemistry: cholesterol. Triglycerides Blood biochemistry: triglycerides. Glycerol. Free fatty acids. Creatinine kinase Blood biochemistry: creatine phosphokinase. Aspartate aminotransferase (ALT) Blood biochemistry: alanine aminotransferase (SGPT, ALT). Alanine aminotransferase (AST) Blood biochemistry: aspartate aminotransferase (AST). Gamma glutamyltransferase (GGT) Blood biochemistry: gamma glutamyltransferase. Alkaline phosphatase (ALP) Blood biochemistry: alkaline phosphatase (ALP). Amylase Blood biochemistry: amylase. Lipase Blood biochemistry: lipase. Trypsin-like immunoreactivity (TLI) Blood biochemistry: trypsin-like immunoreactivity. Hormones: cortisol Blood biochemistry: cortisol , thyroxine Thyroxine assay (free) ; parathyroid hormone PTH assay. Vitamin B12 Blood biochemistry: vitamin B12. Folate Blood biochemistry: folate. Para-aminobenzoic acid Blood biochemistry: para-aminobenzoic acid. C reactive protein. Sampling This article is available in full to registered subscribers Sign up now to purchase a 30 day trial, or Login Tests Methodologies A number of different methodologies may be available for any given test. Availability Many tests are routinely available - if in doubt, contact the laboratory to confirm availability of a specific test. ValiditySensitivity 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. Specificity 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. Example 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 This article is available in full to registered subscribers Sign up now to purchase a 30 day trial, or Login Further ReadingPublicationsRefereed papers Recent references from VetMed Resource and PubMed. Other sources of information Kaneko J J, Harvey J W & Brass M L (eds) (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Boston: Academic Press.