RFPT121201

What’s Behind a RefeRence inteRval?Frances moore, DVm, Diplomate acVp

Interpretation of a patient’s laboratory results requires knowledge of results expected in a population of normal, healthy animals assayed under the same conditions. There are several ways to establish these reference values. One of the most common approaches is to analyze blood/serum samples from a population of healthy animals (i.e., a reference population). The reference population must be similar to the patient population and the assays must be performed under the same laboratory conditions as patient samples (i.e., same analyzer, reagents and handling). Ideally the reference population should reflect the results of at 120 individuals of the same species, breed, age, gender, nutrition and environment as the patient population. In research settings, more specific reference intervals are established in which the reference population reflects not only the species but also the breed, strain, age, gender and the specific research conditions under which the samples are obtained.

Reference intervals are established for each analyte. The intention is to encompass approximately 95% of values obtained from healthy animals (figure 1). Each set of laboratory results is statistically analyzed to determine the appropriate reference interval (figure 2). Reference intervals must be reassessed whenever analytical system, methods or reagents change.

Currently, we are updating our chemistry analyzers in all of our laboratories to an improved analytical system. The process of implementing any new analyzer is not as simple as setting it up and

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What’s Behind a RefeRence inteRval? ..................................1

MaRshfield laBs alpaca Blood dRive .........................................3

Inside This Issue

REFERENCE INTERVAL

2.5% 95% 2.5%

Normal animal population

Figure 1: This graph depicts the relationship between the set of results comprising the reference interval relative to results from a normal population of animals.

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turning it on. Each analytical assay must be validated through a series of tests, including assessments for linearity, precision, reportable range and interferences to ensure the highest quality laboratory results. We must also ensure that all analyzers throughout our system yield similar results. Reference intervals are re-established for each analyte

Validation and re-establishment of reference intervals is no small task. Implementation of the new analyzers requires analysis of hundreds of samples from many species. Although samples from common domestic species (ie, dogs, cats, horses and cows) were fairly easily obtained, acquiring samples of small ruminants required a more concerted effort. Marshfield laboratory technicians worked with a local practitioner, Dr. Barb Kasprowicz, in several well-orchestrated blood “drives” to get samples from goats, sheep and alpacas. With the assistance of several research facilities, reference intervals were established for Yucatan miniature swine, Sprague Dawley rats and purpose bred laboratory sheep.

The results of these studies will be reflected in modified reference intervals effective the week of January 7, 2013. Patient reports will display the new reference intervals for all analytes.

ReferencesGeffre A, Friedrichs KR, Harr KE, Concordet D, Trumel C, Braun JP. Reference values: a review. Vet Clin Pathol 38/3: 288- 298, 2009.

Friedrichs KR, Harr, KE, Freeman KR, Szladovits B, Walton RM, Barnhart KF, Clanco-Chaves J. ASVCP reference interval guidelines: determination of de novo reference intervals in veterinary species and other related topics. Vet Clin Pathol 41/4: 441-453, 2012.

Figure 2. Sample of statistical analysis of serum cholesterol results from reference population of goats. Each analyte was subjected to statistical assessment to establish the reference interval.

MaRshfield laBs alpaca Blood dRiveFrances moore, DVm, Diplomate acVp

Dr. Barb Kasprowicz and Marshfield Labs staff visited Jam’s Alpaca Ranch on Lincoln Road in Vesper, WI on October 30th, 2012 to sample Audrey Hackbarth’s prize animals. These samples are being assayed to establish reference intervals for normal alpacas to which patient results can be compared. Dr. Kasprowicz owns Country Vet in Almond, Wisconsin. Her practice includes dairy and beef cattle, dairy and meat goats, sheep, pigs, horses, alpacas and llamas. She is the farm veterinarian for Jam’s Alpaca Ranch and she graciously agreed to sample the animals for our reference interval studies.

Audrey Hackbarth’s alpacas are raised for their fiber which she uses to make a wide variety of clothing items which highlight the natural colors of the fleece and are on display at the ranch store, which is open to the public. The alpacas are very docile although some of the males required some persuasion in the form of blindfolds and gentle but firm restraint to permit blood sampling.

Despite the cold temperatures and wind, all the samples were obtained without incident. Hematology and chemistry assays have been completed and the results are being tabulated and analyzed to establish alpaca reference intervals.

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Blood sampling from alpacas for reference interval studies. Dr. Kasprowicz (Country Vet; Almond,WI) is performing the venipuncture while Koral Peters (Marshfield Labs technician) restrains the head. Audrey Hackbarth (owner) steadies the rear while Gloria Tew (volunteer) and Judy Pilsner (Marshfield Labs technician) stand ready to receive the sample.

Blood sampling from alpacas for reference interval studies. Dr. Kasprowicz (Country Vet; Almond,WI) is performing the venipuncture while Koral Peters (Marshfield Labs technician) restrains the head. Audrey Hackbarth (owner) holds the flank.

Professional and technical staff with hardy volunteers at alpaca blood drive for reference interval studies. From left: April Schulz1, Judy Pilsner1, Dr. Mary Alice Kettrick1, Gloria Tew2, Adam Lobner1, Audrey Hackbarth3, Dr. Barb Kasprowicz4, and Koral Peters1

1Marshfield Labs staff, 2Jam’s Alpaca Ranch volunteer, 3Ranch owner, 4Veterinarian, owner, Country Vet, Almond, WI

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