Stay afloat in the tsunami: A focus on clinical relevance when partitioning reference intervals

Separating disease and health for indirect reference intervals

The indirect approach to defining reference intervals operates ‘a posteriori’, on stored laboratory data. It relies on being able to separate healthy and diseased populations using one or both of clinical techniques or statistical techniques. These techniques are also fundamental in a priori, direct reference interval approaches. The clinical techniques rely on using clinical data that is stored either in the electronic health record or within the laboratory database, to exclude patients with possible disease. It depends on the investigators understanding of the data and the pathological impacts on tests. The statistical technique relies on identifying a dominant, apparently healthy, typically Gaussian distribution, which is unaffected by the overlapping populations with higher (or lower) results. It depends on having large databases to give confidence in the extrapolation of the narrow portion of overall distribution representing unaffected individuals. The statistical issues involved can be complex, and can result in unintended bias, particularly when the impacts of disease and the physiological variations in the data are under appreciated.

Establishment of reference intervals for plasma protein electrophoresis in Indo-Pacific green sea turtles, Chelonia mydas

Biochemical and haematological parameters are increasingly used to diagnose disease in green sea turtles. Specific clinical pathology tools, such as plasma protein electrophoresis analysis, are now being used more frequently to improve our ability to diagnose disease in the live animal. Plasma protein reference intervals were calculated from 55 clinically healthy green sea turtles using pulsed field electrophoresis to determine pre-albumin, albumin, α-, β- and γ-globulin concentrations. The estimated reference intervals were then compared with data profiles from clinically unhealthy turtles admitted to a local wildlife hospital to assess the validity of the derived intervals and identify the clinically useful plasma protein fractions. Eighty-six per cent {19 of 22 [95% confidence interval (CI) 65-97]} of clinically unhealthy turtles had values outside the derived reference intervals, including the following: total protein [six of 22 turtles or 27% (95% CI 11-50%)], pre-albumin [two of five, 40% (95% CI 5-85%)], albumin [13 of 22, 59% (95% CI 36-79%)], total albumin [13 of 22, 59% (95% CI 36-79%)], α- [10 of 22, 45% (95% CI 24-68%)], β- [two of 10, 20% (95% CI 3-56%)], γ- [one of 10, 10% (95% CI 0.3-45%)] and β-γ-globulin [one of 12, 8% (95% CI 0.2-38%)] and total globulin [five of 22, 23% (8-45%)]. Plasma protein electrophoresis shows promise as an accurate adjunct tool to identify a disease state in marine turtles. This study presents the first reference interval for plasma protein electrophoresis in the Indo-Pacific green sea turtle.

Basal plasma concentrations of routine variables and packed cell volume in clinically healthy adult small-sized dogs: effect of breed, body weight, age, and gender, and establishment of reference intervals

BACKGROUND

Plasma variables may be affected by breed or body weight (BW). Small-sized dogs are very common, but no specific reference intervals (RI) are used.

OBJECTIVES

The primary objective of this prospective study was to assess the potential effect of breed, BW, age, and sex on routine plasma analytes and packed cell volume (PCV) in small-sized dogs. A secondary objective was to establish RI in this small-sized population.

METHODS

Blood was sampled under standardized conditions from healthy dogs. PCV and 15 routine plasma variables were measured at the same laboratory. Effects of breed, BW, age, and sex were tested using a general linear model. The procedure recommended by the Clinical and Laboratory Standards Institute was used to establish RI.

RESULTS

In this study, 154 healthy dogs from 7 breeds were prospectively included. Although a significant effect of breed, BW, sex, or age was evidenced for most variables (except plasma sodium, phosphates, and triglycerides), it was considered as clinically irrelevant. More strikingly, the percentage of values in the reference sample group under the lower limit of the laboratory's RI ranged from 3.8% to 76.6% for 9 variables, and those higher than the upper limit of the laboratory's RI ranged from 4.5% to 9.7% for 7 variables. For example, the RI for creatinine in small-sized dogs was 45-90 μmol/L (vs 54-144 μmol/L for the general dog population).

CONCLUSION

Specific RI should be considered for PCV and selected plasma variables in small-sized dogs.

Echocardiography and conventional Doppler examination in clinically healthy adult Cavalier King Charles Spaniels: effect of body weight, age, and gender, and establishment of reference intervals

OBJECTIVES

The objectives of this study were (1) to assess the potential effect of body weight (BW), age, and gender on the most commonly used echocardiographic and conventional Doppler variables in a large population of healthy Cavalier King Charles Spaniels (CKCS), and (2) to establish the corresponding reference intervals (RI).

ANIMALS

134 healthy adult CKCS.

METHODS

Ultrasound examinations were performed by trained observers in awake dogs. M-mode variables included left ventricular (LV) end-diastolic and end-systolic diameters, LV free wall and interventricular septal thicknesses at end-diastole and end-systole, and LV fractional shortening (FS%). The left atrium (LA) and aortic (Ao) diameters were measured using a 2D method, and the LA/Ao was calculated. Pulsed-wave Doppler variables included peak systolic aortic and pulmonary flow velocities, mitral E and A waves, and E/A ratio. Effects of BW, age, and gender on these 15 variables were tested using a general linear model, and RIs were determined by applying the statistical procedures recommended by the Clinical and Laboratory Standards Institute.

RESULTS

A significant BW effect was observed for all variables, except LA/Ao, FS%, and mitral E/A ratio. A significant but negligible effect of gender and age was also observed for 5/15 and 4/15 of the tested variables, respectively. Only the BW effect on M-mode variables was considered as clinically relevant and the corresponding regression-based RIs were calculated.

CONCLUSIONS

Body weight should be taken into account when interpreting echocardiographic values in CKCS, except for LA/Ao, FS%, and mitral E/A ratio.

Age-related changes in biochemical and hematologic variables in Borzoi and Beagle puppies from birth to 8 weeks

BACKGROUND

Nonspecific signs of illness and availability of only limited information about expected biochemical and hematologic values in puppies make formulation of a differential diagnosis challenging for veterinarians.

OBJECTIVES

The objectives of this prospective study were to describe age-related changes in biochemical and hematologic variables in Borzoi and Beagle puppies from birth to 8 weeks and to compare results with adult reference intervals (RIs).

METHODS

Biochemical and hematologic analytes in blood collected in heparin and EDTA from 31 clinically healthy puppies (21 Beagle and 10 Borzoi dogs) were measured or calculated each week from birth to 8 weeks of age. RIs were calculated using the parametric robust method after Box-Cox transformation.

RESULTS

There were no significant differences between values of puppies and adults for ALT activity, glucose concentration, MCHC, WBC count, and platelet count. Total protein concentration, RBC count, and HCT were lower and creatine kinase activity was higher in puppies of all ages compared with these variables in adults. Compared with adult RI, in puppies urea concentration was higher at birth and week 1, creatinine concentration was lower at weeks 1-5, ALP activity was higher at all weeks except for weeks 4 and 6, hemoglobin concentration was lower at weeks 1-8, MCV was higher at birth and week 1, and reticulocyte count was higher at all weeks except week 1. Statistically, mixed models accounted for evaluation of the same puppies each week and in most cases demonstrated an effect of age and sometimes breed. Some reference intervals should be used with caution owing to potential outliers. The 90% confidence intervals exceeded those recommended by the International Federation of Clinical Chemistry.

CONCLUSIONS

Clinicians should be aware of temporal changes in biochemical and hematologic values for puppies during the first 2 months of life to avoid misinterpretation of results.