The way to diagnose cushing by the cat.
Introductie:
There are many reasons why veterinary clinicians may wish to measure corticoid levels in their patients.
One is to aid in the diagnosis of cushings disease (hyperadrenocorticism), a disease seen commonly in the dog.
In the cat, cushings is diagnosed much less frequently and it is usually in a late stage of the disease.
In most circumstances, it is only detected because the cat has consequentially developed diabetes mellitus (Rijnberk1996). Due to such detrimental metabolic effects of elevated corticoid levels, it is important that cushings disease is diagnosed early.
A common method in dogs of diagnosing cushings, is by establishing the corticoid/creatinine ratio in the urine (Rijnberk 1988). It is also possible to use this method to diagnose cushings in the cat (Goossens 1995, Henry 1996). However, in cats this way has always been more difficult, because corticoid can rise within minutes if the patient is stressed (Bird 1973, Willemse 1993). Sufficient stress may occur by either manual bladder expression or by cystocentesis - two usual methods of urine collection in cats.
One non-invasive and non-stressful method of collecting urine samples in the cat is to collect the urine in the familiar surroundings of it's own home using a litter tray. However, for diagnostic purposes, it is important that the litter does not affect the urine. The current study investigates whether or not Katkor litter in any way influences the composition of urinary corticoid and creatinine after it has passed, and thus decrease the difficulty in diagnosing cushings in the cat.
Materials and methods:
Through measuring concentrations of corticoid, creatinine, and the corticoid : creatinine ratio, in the urine mixed with, and not mixed with Katkor, it will be able to be established whether or not the Katkor is influencing the levels of these substances in the urine.
Cats were used for the study were from the main department of Geneeskunde van Gezelschapsdieren van de Universiteit Utrecht where they were grouped together in 3 enclosures each of which contained 9 cats.
At 8.00 am, the cat litter trays were removed from each of the enclosures, so that the cats did not have a litter tray and would hold on to their urine. At 1.30 pm, each of the cats had their bladder palpated for size. Fourteen cats were selected for the size of their full bladders. The urine from these cats was collected either by cystocentesis, or bladder massage, where the urine was excreted, and then collected with a syringe.
The syringes were labelled so that the urine from each particular cat could be identified. Half of the urine from each cat was put into a petrie dish filled with Katkor, and half put into an empty petrie dish. All 28 dishes stayed 3 to 4 hours at room temperature with minimal light. After 3-4 hours the urine was removed from the dish in a new syringe, and placed in tubes numbered 1 to 14 and 1a to 14a ("a" tubes for the Katkor samples). These tubes were placed in the fridge for 4 days before the corticoid/creatinine ratios were measured.
The cortisol from each syringe was measured using radioimmunoassay, according to Rijnberk 1988. The creatinine level was measured according to the "Jaffe kinetic method".
Results:
The paired urine samples were compared using a paired student t-test where P < 0.05 significance. There was no significant difference (P=0.72) between the cortisol concentration
from the urine mixed with Katkor (average = 271 nmol/l) and the urine not mixed with Katkor (average = 267 nmol/l) (figure 1), or from the creatinine concentration of the urine mixed
with katkor (average=19051umol/l) and the urine not mixed with Katkor (average = 18987 umol/l) (figure 2), or in difference between the corticoid/creatinine ratio of the urine mixed with Katkor (average = 13.36 x 10 -6) and the urine not mixed with Katkor (average = 13.24 x 10 -6)(figure 3) was also not significant (P=0.81).
| Cat number |
Cortisol (nmol/l) from urine
not mixed with katkor |
Cortisol (nmol/l) from urine
mixed with katkor |
| 1 |
390 |
437 |
| 2 |
785 |
823 |
| 3 |
232 |
240 |
| 4 |
263 |
218 |
| 5 |
201 |
187 |
| 6 |
21 |
16 |
| 7 |
227 |
260 |
| 8 |
59 |
52 |
| 9 |
93 |
114 |
| 10 |
92 |
93 |
| 11 |
55 |
62 |
| 12 |
288 |
184 |
| 13 |
754 |
812 |
| 14 |
288 |
307 |
Figure 1. Cortisol concentration of 14 urine samples mixed with Katkor (average 271 nmol/l) and not mixed with Katkor (average = 267 nmol/l p = 0.72).
| Cat number |
Creatinine (umol/l) from urine
not mixed with katkor |
Creatinine (umol/l) from urine
mixed with katkor |
| 1 |
18500 |
18820 |
| 2 |
19180 |
19050 |
| 3 |
19520 |
20090 |
| 4 |
19150 |
19300 |
| 5 |
15540 |
15920 |
| 6 |
9510 |
9430 |
| 7 |
15890 |
16300 |
| 8 |
19550 |
19470 |
| 9 |
23300 |
23190 |
| 10 |
18610 |
18460 |
| 11 |
13190 |
13030 |
| 12 |
23120 |
23150 |
| 13 |
27230 |
27280 |
| 14 |
23530 |
23230 |
Figure 2. Creatinine concentration from 14 urine samples mixed with Katkor
(average 19051 umol/l) and not mixed with Katkor (average = 18987 umol/l p=0.37).
| Cat number |
Cortisol / creatinine ratio
(x10-6) from urine not mixed with katkor |
Cortisol (nmol/l) from urine
(x10-6) from urine not mixed with katkor |
| 1 |
21 |
23 |
| 2 |
41 |
43 |
| 3 |
12 |
12 |
| 4 |
14 |
11 |
| 5 |
13 |
12 |
| 6 |
2.2 |
1.7 |
| 7 |
14 |
16 |
| 8 |
3 |
2.7 |
| 9 |
4 |
4.9 |
| 10 |
4.9 |
5 |
| 11 |
4.2 |
4.8 |
| 12 |
12 |
7.9 |
| 13 |
28 |
30 |
| 14 |
12 |
13 |
Figure 3. Cortisol/Creatinine ratios from 14 urines mixed with Katkor
(average = 13.36 x 10 -6) and urine samples not mixed with Katkor (13.24 x 10 –6 p= 0.81).
The results clearly show that there are no significant differences between the urine with Katkor and the urine without Katkor. Thus showing that Katkor is non-absorbent and in no way influences the composition of the urinary corticoid, creatinine, or corticoid/creatinine ratio
DDiscussion:
Because cats are so susceptible to stress, corticoid levels may temporarily increase (Bird 1973, Willemse 1993). In the present study, cat number 2 (figure 3) showed corticoid/creatinine levels which were higher than the cushings cut off level of 36 X 10 -6 (Goossens 1995). This cat did not show any clinical signs of cushings and it can be safely
assumed that the method of urine collection employed, was responsible for this result.
Although a stressful level of urine collection was employed during the present study, this did not interfere with the comparison of concentrations tested in the two urine samples; those with Katkor and those without. Regardless of the initial concentrations, there was no difference between the two groups.
It has previously been established that if a urine sample is collected from an unstressed cat, then it is possible to diagnose cushings from the corticoid concentrations in this sample (Goossens 1995). This is of great benefit to a clinician, because cushings is difficult to detect in cats, and it is also preferable to check cats diagnosed with diabetes mellitis. However, a stress free urine sample is required, which is best obtained in their home environment.
Therefore, to use urine in the diagnosis of cushings, it must not be collected by cystocentesis or manual expression. A stress free home environment is necessary, and the present study establishes that Katkor is now proven for use as a non-absorbent litter allowing an accurate
subsequent analysis of the urine.
Drs. Mabet de Lange
Geneeskunde van Gezelschapsdieren
Universiteit Utrecht
March 2001
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