Diagnostic efficacy of the leukogram and the chemiluminometric ACTH measurement to diagnose canine hypoadrenocorticism

Background and objective: The gold standard in the diagnosis of canine hypoadrenocorticism (HA) is the adrenocorticotropin (ACTH) response test. As synthetic ACTH (tetracosactide [Synacthen®]) is currently not available in the European Union, the evaluation of other diagnostic tests seemed warranted. The diagnostic efficacy of electrolytes, the leukogram and endogenous ACTH concentrations to diagnose HA was investigated. Material and methods: The medical records of 145 dogs with clinical signs suspect for spontaneous HA were included in a retrospective study. HA was diagnosed (n = 38) or ruled out (n = 84) by using an ACTH response test. In 23 patients HA was excluded by basal cortisol measurement. The diagnostic performance of various variables was assessed based on receiver operating characteristic (ROC) curves and by calculating differential positive rates. A decision tree (IBM SPSS Decision Trees 20, IBM Corporation) was constructed with the variables neutrophil to lymphocyte ratio (N/LR) and sodium to potassium ratio (Na/KR) to illustrate the diagnostic efficacy of the respective test results. Results: The best single variables to diagnose HA were the endogenous ACTH concentration (area under the ROC curve [ROC AUC] 0.97; cutoff > 50 pmol/l: sensitivity 96%, specificity 100%) and the Na/KR (ROC AUC 0.905; cutoff ≤ 22: sensitivity 92%, specificity 91%). The diagnostic performance of various variables of the leukogram was poor to moderate (ROC AUC 0.625–0.828). 68% of dogs with HA had a Na/KR ≤ 22 and a N/LR ≤ 2.3, a combination not observed in dogs with non-adrenal diseases. Conclusion and clinical relevance: As secondary HA is very rare, endogenous ACTH measurement is a very good alternative to the traditional ACTH response test. Data also suggest that the combination of a Na/KR ≤ 22 and a N/LR ≤ 2.3 is highly specific and can be used to rule in HA.

Hyperthyroidism in dogs caused by consumption of thyroid-containing head meat

Two female spayed dogs belonging to the same owner were admitted for further examinations because of clinical signs and laboratory values compatible with hyperthyroidism. Sonography of the ventral aspect of the neck revealed small thyroid glands in both dogs. The hypothesis that the dogs suffered from alimentary hyperthyroidism caused by feeding head meat containing thyroid gland tissue was confirmed by consultation of the slaughtering plant, determination of iodine concentrations in deep-frozen samples and hormone measurements in 5 other dogs receiving head meat from the same supplier. After changing the diet, thyroxine concentrations declined and clinical signs were no longer observed.

[Buccal glucose measurements in dogs using safety lancets for blood sampling]

OBJECTIVE

Glucose measurements at the pinna or paws are an important part of the management of diabetic dogs. Despite extensive rubbing or warming of the testing site, an adequate blood sample cannot always be obtained. Therefore, the objective of this study was to evaluate the lip as an alternative sampling site with respect to practicability and tolerance by the dogs and reliability of the measured values.

MATERIAL AND METHODS

Nine clinic-owned male-castrated healthy beagles were included in this prospective study. Glucose measurements were performed using a glucometer developed for veterinary use, before and 15 minutes after oral application of glucose syrup. Capillary blood was collected using two commercially available safety lancets (Wellion Safety lancet [23 gauge] and Wellion Safety lancet special [blade 0.8 mm]) at the buccal mucosa of the upper lip and at the pinna. Measured values were compared with those obtained from venous plasma (reference method).

RESULTS

Buccal glucose measurements were easy to perform and were well tolerated by the dogs without obvious pain reactions. There was no difference between the glucose concentrations from the lip samples and those determined using the reference method (p = 0.793, F < 1). The glucose application had no effect on the observed differences (reference value minus glucometer value; p = 0.63, F < 1). However, in one dog, a clinically problematic discrepancy of 3.6 mmol/l was observed. The special lancet caused noticeable secondary bleeding in two dogs.

CONCLUSION AND CLINICAL RELEVANCE

The results of this study indicate that the buccal mucosa is a convenient and reliable alternative sampling site for glucose measurements in dogs. Problematic deviations from reference values are possible after oral glucose application and the use of blade-like needles is not encouraged.

Diagnostic efficacy of the leukogram and the chemiluminometric ACTH measurement to diagnose canine hypoadrenocorticism

BACKGROUND AND OBJECTIVE

The gold standard in the diagnosis of canine hypoadrenocorticism (HA) is the adrenocorticotropin (ACTH) response test. As synthetic ACTH (tetracosactide [Synacthen®]) is currently not available in the European Union, the evaluation of other diagnostic tests seemed warranted. The diagnostic efficacy of electrolytes, the leukogram and endogenous ACTH concentrations to diagnose HA was investigated.

MATERIAL AND METHODS

The medical records of 145 dogs with clinical signs suspect for spontaneous HA were included in a retrospective study. HA was diagnosed (n = 38) or ruled out (n = 84) by using an ACTH response test. In 23 patients HA was excluded by basal cortisol measurement. The diagnostic performance of various variables was assessed based on receiver operating characteristic (ROC) curves and by calculating differential positive rates. A decision tree (IBM SPSS Decision Trees 20, IBM Corporation) was constructed with the variables neutrophil to lymphocyte ratio (N/LR) and sodium to potassium ratio (Na/KR) to illustrate the diagnostic efficacy of the respective test results.

RESULTS

The best single variables to diagnose HA were the endogenous ACTH concentration (area under the ROC curve [ROC AUC] 0.97; cutoff > 50 pmol/l: sensitivity 96%, specificity 100%) and the Na/KR (ROC AUC 0.905; cutoff ≤ 22: sensitivity 92%, specificity 91%). The diagnostic performance of various variables of the leukogram was poor to moderate (ROC AUC 0.625-0.828). 68% of dogs with HA had a Na/KR ≤ 22 and a N/LR ≤ 2.3, a combination not observed in dogs with non-adrenal diseases.

CONCLUSION AND CLINICAL RELEVANCE

As secondary HA is very rare, endogenous ACTH measurement is a very good alternative to the traditional ACTH response test. Data also suggest that the combination of a Na/KR ≤ 22 and a N/LR ≤ 2.3 is highly specific and can be used to rule in HA.

Configuration of antibodies for assay of urinary cortisol in dogs influences analytic specificity

Whether the variation in the reported urinary corticoid-to-creatinine ratio in dogs is affected by the application of 2 commonly applied anticortisol antibodies was investigated. Free-catch morning urine samples of 50 healthy dogs were analyzed in duplicate with the use of 2 different polyclonal antibodies (antibody A and B) raised in different rabbits. Antibody A was raised against cortisol-3-carboxymethyl-oxime and antibody B against cortisol-21-hemisuccinate linked to BSA. Enzyme immunoassays were applied by using corresponding biotinylated labels. To examine possible cross-reactions with conjugated and nonconjugated cortisol metabolites, EIA measurements were performed with urine samples both before (directly assayed) and after diethyl-ether extraction, as well as after reversed-phase HPLC. Although the results correlated (P < 0.001), urinary corticoid concentrations and accordingly the urinary corticoid-to-creatinine ratios were 8 times higher when using antibody A than when using antibody B (mean ± SD corticoid concentrations, 223 ± 131 vs 29 ± 12 nmol/L; P < 0.001). Irrespective of the antibody used, extraction significantly decreased measured corticoid concentrations (antibody A, 158 ± 120 nmol/L; antibody B, 15 ± 8 nmol/L; P < 0.001), but the decrease was conspicuous when antibody A was used. Antibody A cross-reacted significantly with polar (eg, conjugated) metabolites, clearly depicted in the chromatogram by 3 additional peaks in earlier fractions well separated from cortisol. In contrast the assay that used antibody B was specific, showing only 1 major peak in the fractions eluting authentic cortisol. In summary, the study indicates that the configuration of the antibody considerably influences the analytic specificity of cortisol assays and underlines the pivotal importance of assay validation for each species and sample material.

Point-of-care β-hydroxybutyrate measurement for the diagnosis of feline diabetic ketoacidaemia

OBJECTIVES

To evaluate accuracy and precision of a hand-held ketone meter measuring β-hydroxybutyrate and to determine its diagnostic performance to rule out ketoacidaemia in diabetic cats.

METHODS

The ketone meter was validated by calculating within-day precision at different β-hydroxybutyrate concentrations and by comparison with a laboratory method. To determine its diagnostic performance to diagnose ketoacidaemia, 217 sets of data (venous blood gas analysis and β-hydroxybutyrate measurements) were retrospectively analysed. Sensitivities and specificities were calculated with the help of receiver-operating characteristic curves.

RESULTS

The ketone meter reliably detected β-hydroxybutyrate at concentrations >0·1 mmol/L and reproducibility was acceptable. Measurements highly correlated with laboratory results (r=0·97; P<0·001), but a significant negative bias was found at high concentrations. A β-hydroxybutyrate concentration of >2·55 mmol/L had a sensitivity of 94% and a specificity of 68% for diagnosing ketoacidaemia. Many cats with high β-hydroxybutyrate concentrations and normal blood pH had an elevated chloride gap suggestive of superimposed hypochloraemic metabolic alkalosis.

CLINICAL SIGNIFICANCE

The commercially available point-of-care ketone meter Precision Xtra is a valid tool to measure β-hydroxybutyrate in diabetic cats. Concentration <2·55 mmol/L enable ketoacidaemia to be excluded and should lead to redirection of differential diagnoses.