Tear glucose, creatinine, and urea nitrogen concentrations in cats with normal or increased plasma concentrations

Abstract

Objective The aim of the study was to determine the lacrimal fluid (LF) contents of glucose, urea nitrogen, and creatinine in cats. Animal studied A total of 96 cats were included in the study. Procedure Venous blood and LF samples were collected. For LF sampling, three small polyurethane sponges were placed in the ventral fornix of both eyes. Both LF and plasma concentrations of glucose, urea nitrogen, and creatinine were quantitatively analyzed and compared. Result Glucose (n = 40) and urea nitrogen concentrations (n = 42) measured in LF from both eyes highly correlated. While there was a very strong correlation (ρ = 0.97) between urea nitrogen concentrations in blood plasma and the corresponding tear levels (with the median LF urea nitrogen being 109% of that measured in plasma), the LF glucose concentrations were significantly lower than the corresponding plasma concentrations (with only 13% of the blood glucose concentration detected in the LF). The creatinine concentrations in tears were much lower than those in plasma, and LF creatinine was detectable in only 12/48 cats (25%). Hence, a comparison of the LF creatinine concentrations between both eyes or with the corresponding plasma creatinine concentration was not possible. Conclusion Measurement of LF urea nitrogen concentrations in cats appears to be reliable and might have potential clinical utility. Measurement of LF glucose concentrations is less reliable but may still be useful in some cats. Creatinine is not reliably detected in the LF in cats. Further studies determining clinical utility of LF metabolites in cats and other companion animals are warranted.

Quantification of tear glucose levels and their correlation with blood glucose levels in dogs

“…Those results were similar to our findings in that there was a significant difference in TG concentrations between normal and hyperglycaemic groups. These findings were also consistent with the results of an earlier study that quantified TG in cats with normal or increased BG concentrations (Steinmetz et al., 2019). However, the TG concentrations in diabetic dogs (Cullen et al., 2005) (median: 6 mmol/L) and in hyperglycaemic cats (Steinmetz et al., 2019) (median: 1.50 mmol/L) were higher than those in the hyperglycaemic phase in the present study (median: 0.80 mmol/L).…”

“…(median: 6 mmol/L) and in hyperglycaemic cats(Steinmetz et al, 2019) (median: 1.50 mmol/L) were higher than those in the hyperglycaemic phase in the present study (median: 0.80 mmol/L). The possible reasons for these variations are as follows.…”

“…In addition, there is a barrier in the epithelium of the cornea and conjunctiva that prevents glucose from moving into the tear fluid (van Haeringen & Glasius, 1977). In a previous study on cats, the median TG concentration was 13% of the BG concentration, while the median tear urea nitrogen concentration was 109% of that measured in blood plasma (Steinmetz et al, 2019). Similarly, previous studies in humans found very low TG levels in diabetic patients, while the concentration of urea nitrogen in the tears was within the normal range in serum (Kang et al, 1988;van Haeringen & Glasius, 1977).…”

“…However, there are only limited studies of the association between BG and TG in small animals (Cullen et al., 2005; Steinmetz et al., 2019). To date, only semi‐quantitative analysis of TG in dogs using a urine dipstick (Cullen et al., 2005) and a comparison of TG and BG concentrations in cats have been reported (Steinmetz et al., 2019). No studies have been conducted to quantify TG in dogs or to identify changes in TG in association with changes in BG.…”

“…However, there are only limited studies of the association between BG and TG in small animals (Cullen et al, 2005;Steinmetz et al, 2019).…”