How should I test for a diabetes insipidus?

RE: How should I test for a diabetes insipidus?

Mellora Sharman — Wed, 10 Jan 2024 14:09:50 GMT

Hi Elizabeth!

Thanks for the update - I'd suggest reviewing your SDMA, and creatinine concentrations against the IRIS Staging Guidelines which you can find at www.iris-kidney.com . I can appreciate the concern for something else contributing, but if you have a creatinine and SDMA concentration compatible with CKD, then this would be the most likely cause for me - the improvment with antibiotics might lead me to want to really check for pyelonephritis which I wouldn't exclude non the basis of a 'quiet' sediment alone.

Best Wishes,

Mellora

RE: How should I test for a diabetes insipidus?

Elizabeth — Tue, 09 Jan 2024 15:11:40 GMT

Thank you , Mellora. Not at work at the moment but as far as I can remember the Sdma was 14 with a marginally raised urea and mid range creatinine. Now the urea and creatinine are both mid-range with the slightly increased sdma. It has been on a renal diet following it’s initial blood and urine results in September , when dealt with by a collegue, but I was concerned that we were missing something because of the consistently hyposthenuric results combined with the extreme PU/PD with on the whole normal/mildly abnormal renal parameters. No sediment in urine. No appetite or skin changes. She did start eating ravenously after I gave her some synulox after collecting urine for culture - I gave it incase she did have a pyelonephritis whilst waiting for the urine results as she had been inappetant for the last week.

RE: How should I test for a diabetes insipidus?

Mellora Sharman — Mon, 08 Jan 2024 09:44:31 GMT

Hi Elizabeth,

Diabetes Insipidus is most often a rule-out diagnosis - ie we exclude all other causes of PU/PD.

Causes of PU/PD where USG is consistently <1.020 include

- Pyometra

- Hypercalcaemia

- Hepatic insufficiency

- Cushing's Syndrome

- Pyelonephritis

- Hypokalaemia

- Addison's Disease

- Hyperthyroidism

- Renal Disease

(Phaeochromocytoma)

So my approach tends to be to evaluate the possibility of all of the above, which I'm sure you've already considered, and a few of which may well be excluded on the basis of your bloodwork already.

You mention that SDMA is 15 ug/dL which is above the upper limit of the RR and may be consistent with early CKD. What is the creatinine concentration in this dog? Although it may be 'normal' - it's important to remember that IRIS Stage 1 and 2 CKD creatinine values can fall within the normal range (see www.iris-kidney.com for staging information), so if you do have an SDMA that is increased above the RR, CKD may be the most likely cause of PU/PD in this case - is there any particular reason that you have decided that CKD is not likely in this case? Is it because urine is not isosthenuric - as that wouldn't completely exclude early CKD as a cause for me.

Do you have any evidence of an active sediment - pyuria, haematuria, bacturia in this case? It can be important to culture these types of cases either way and dilution may minimise sediment findings to a degree. Pyelonephritis can be a challenging rule-out, and repeated UA and culture results are often ideal to evaluate this more completely +/- diagnostic imaging.

Testing for other causes may depend upon other clinical signs - ie if there is polyphagia and skin/coat changes, further testing for Cushing's might be indicated. You could look at the Prediction Scoring system for Cushing's if you feel this might be a possibility, although the normal ALkP might make this less likely if no other signs are present. If calcium is high normal, then an ionized calcium might be ideal to ensure ionized hypercalcaemia is not present.

The possibility of CKD would really make a water deprivation test unrequired, but also risky for this patient. I tend not to advocate for water deprivation tests (modified or otherwise) due to the inherent risk of the test - ie often these patients cannot concentrate urine due to interference with AHD activity and/or medullary washout - so water deprivation testing can get you into a whole world of hurt with regard to hydration and electrolyte imbalances super quickly, and even with a modified test very very close monitoring is required of body weight / hydration status and electrolyte values.

A DDAVP response test is always my preferred approach, however it is important to remember that for a wide range of causes, then mechanism of PU/PD is interference with ADH activity and as DDAVP is a more potent form of ADH, we can see a non-specific response, and therefore excluding things to the best of our ability otherwise is important.

If HCT is 38%, and you feel some hydration deficit is present, then a mild anaemia may be present and reflect chronic / inflammatory disease.

I hope this helps!

Best wishes,
Mellora

RE: How should I test for a diabetes insipidus?

Mayank Seth — Mon, 08 Jan 2024 09:13:53 GMT

A desmopressin trial is unlikely to harm BUT dogs with psychogenic DI can be mildly hyponatraemic due to excessive free water and desmopressin can also be associated with mild hyponatraemia / hypernatraemia due to the same. Hypertension secondary to desmopressin ahs been documented and if your dog has, for example, vascular CNS disease leading to its psychogenic PD or primary DI then there is a theoretical basis for making the situation worse. I would be sure the dog is normotensive and has a very normal serum osmolality before going down this route.

Given the mild SDMA elevation, if this is persistent then the PUPD could be stage 1 CKD if this is consistent, although the hyposthenuric urine makes this less likely. If there is CKD then BP is particualrly important to monitor.

A modified water dep trial is a scary thing to do and I've very rarely done it. If you are monitoring Na and blood pressure then I agree a desmopressin is generally the better thing to do (after bloods, urine, imaging etc) but one can do a water dep trial. You just need to make sure you are doing it properly, checking USG, weight, crea and electrolytes at least a couple of times per day. You can do that with free catch samples etc but its scary, costly and labour intensive.

Whatever you do, keep us updated!

RE: How should I test for a diabetes insipidus?

David Mills — Mon, 08 Jan 2024 00:10:20 GMT

[quote userid="24356" url="~/f/clinical-questions/30867/how-should-i-test-for-a-diabetes-insipidus/243335#243335"]What are the consequences of desmopressin in a dog without DI? [/quote]

Won't do any harm, may treat the signs, but as others have said I'd be thinking senility-related psychogenic PD at that age.

(and any tumour isn't going to be treatable realistically)

RE: How should I test for a diabetes insipidus?

Neil Wheadon — Sun, 07 Jan 2024 19:03:41 GMT

How common is Diabetes Insipidus?

In all the years of locumming in many practices, I have never seen a repeat prescription for desmopressin/ddAVP etc.

I remember 32 years ago, fresh out of college really looking for these and never finding one. I have though seen many cases of a very low specific gravity and many of these seem to self cure or lead to nothing.

I put many down to phsycogenic polydipsia now (if all tests available to a GP vet are negative) and tell the client to moniter.

Neil

RE: How should I test for a diabetes insipidus?

Elizabeth — Sun, 07 Jan 2024 13:47:23 GMT

I have mentioned imaging for a tumour hunt. Z

What are the consequences of desmopressin in a dog without DI? If we rule out all he treatable causes of hypostheuric USG , will I do much damage by trialling it?

RE: How should I test for a diabetes insipidus?

Utlendigur — Sun, 07 Jan 2024 13:36:17 GMT

Just another differential to consider....friend's dog (VN). Extensive work up by neighbouring practice NAD so they finally even did a water deprivation test. Provisionally diagnosed as diabetes insipidus. Responded well to desmopressin. Then several weeks later developed sudden ascites, collapse, low BP and was diagnosed at referral as pheochromocytoma with a huge thrombus in the caudal vena cava. Might be worth an abdominal ultrasound by someone confident at assessing adrenals?

RE: How should I test for a diabetes insipidus?

Elizabeth — Sun, 07 Jan 2024 10:14:25 GMT

Collie cross, 15 year old. Bloods pretty much normal - liver parameters mid range, no stress leukogram. Had seemed bright and well but started to go downhill this last week - off food. No palpable tumours. Urine normal apart from usg. Have done lddst and urine culture but no results yet.

RE: How should I test for a diabetes insipidus?

Clive Ansell — Sat, 06 Jan 2024 12:44:31 GMT

What breed and age is the dog? any concurrent issues?

RE: How should I test for a diabetes insipidus?

Elizabeth — Sat, 06 Jan 2024 08:20:16 GMT

Thanks all.

RE: How should I test for a diabetes insipidus?

Clive Ansell — Fri, 05 Jan 2024 10:00:59 GMT

I would echo what the others have already said, rule out other causes with routine blood work and urinalysis, including urine C&S and tests for Cushings.

One difficult differential to exclude would be psychogenic polydipsia; had a case in 2023, responded well to selegiline (Selgian), a young highly strung Border Collie, that was known to previouly produce normal concentarted urine.

I don't know if there is an available assay for ADH, I'm not aware of one. Even so, a negative result would only exclude primary DI.

I've never had much success with water deprivation tests, usually because time limited in a day only practice.

[quote userid="12930" url="~/f/clinical-questions/30867/how-should-i-test-for-a-diabetes-insipidus/243317#243317"]does it matter if it is primary central DI or other things that respond to desmopressin for the average case? Or put another way, if desmopressin treats the only symptoms effectively, does it matter what the cause of those symptoms are?[/quote]

Probably not.

If I've excluded other ddx's as best I can that is what I would do/have done.

RE: How should I test for a diabetes insipidus?

Beats — Fri, 05 Jan 2024 09:09:39 GMT

If you have ruled out other things that are significant and obvious, and the only clinical sign is PUPD, and it responds to desmopressin, then does it matter if it is primary central DI or other things that respond to desmopressin for the average case? Or put another way, if desmopressin treats the only symptoms effectively, does it matter what the cause of those symptoms are?

I'd include bile acids in the routine blood work for case like this re shunts typically. Also I check the sediment (having spun it a few times to concentrate about 3-5ml worth) for bacteria. I'd probably do a UCCR to try to rule out cushings also.

RE: How should I test for a diabetes insipidus?

Rob Loxley — Fri, 05 Jan 2024 08:06:33 GMT

If you've ruled out other differentials (incl cushings) then I'd be more minded for a desmopressin trial than a modified water deprivation test (as they have certain risks but practically take a lot of time and we're just a daytime practice), but you need to rule out the other things that will also respond to desmopressin than primary central DI.