Mismatching urinalysis results

Re: Mismatching urinalysis results

Kate Richardson — Wed, 02 Oct 2013 17:04:09 GMT

Thanks Graham for the clarity on Idexx' advice and on the sampling procedure. Maybe the directory should be updated to advise how to submit urine samples obtained by different means to avoid confusion?

No need for the apology! Hope you all had a good holiday!

Any other pathologists out there want to comment on what their lab advises for urine sample transport?

Re: Mismatching urinalysis results

Graham Bilbrough — Tue, 01 Oct 2013 14:57:50 GMT

Hi, All

Sorry for the slow reply--I have just returned from a holiday with my family in Somerset :)

The Rolands et al 2011 paper does indeed detail a study organized by the University of Liverpool, with submissions to IDEXX Reference Laboratory. It makes for interesting reading. Crucially, it documents samples obtained exclusively by cystocentesis at a referral hospital.

Almost all of the samples submitted to IDEXX come from practitioners using free-catch. Furthermore, even when the submitter has "done a cysto", it is not usually marked on the submission form. Using boric acid leads to more false negatives. The benefit of plain samples may be lost with free-catch urine as bacterial overgrowth with contaminants is much, much more likely. For brevity, the Directory of Service details boric acid.

The team on our telephone hotline encounter this question relatively frequently and explain how that if submitting a cysto sample, it should be indicated and we can consider culture of the boric acid sample and/or the plain sample.

I hope that helps.

Best wishes

Re: Mismatching urinalysis results

Martin Atkinson — Mon, 30 Sep 2013 17:08:02 GMT

Maybe I'm missing the point here but isn't the rule: free catch into boric acid as it is supposed to knock out the commensals but not the pathogenic bacteria, and sterile cysto samples into plain tube as there is virtually no risk of contamination so what grows is what was in the urine and nothing is stunted by the boric acid. The logic of using boric acid has always bothered me, presumably as urine is normally acidic anything surviving in it is by definition from the urine because alkaline loving commensals will have been knocked out but as a predisposing factor for cystitis is alkaline urine this logic falls down a bit!

Re: Mismatching urinalysis results

James Laidlaw — Mon, 30 Sep 2013 14:22:14 GMT

[quote user="Michael Woodhouse"]

I follow the lab's sampling instructions. Idexx still request samples in boric acid so they get samples in boric acid.

If they request them in a used, but well rinsed jam jar that is what they will get.

[/quote] Having spoken to one of the internal medics at idexx this year, they would prefer cystocentesis samples in plain sample pots. Despite this, they said the majority of their culture samples are free catch in boric which is not ideal. Try giving them a call and see what they say.

Re: Mismatching urinalysis results

Kate Richardson — Mon, 30 Sep 2013 12:52:03 GMT

[quote user="Michael Woodhouse"]I follow the lab's sampling instructions. Idexx still request samples in boric acid so they get samples in boric acid.[/quote]

That's a fair enough point but we have to ask why Idexx are still requesting samples this way when the evidence suggests it is not appropriate.

Re: Mismatching urinalysis results

Michael Woodhouse — Mon, 30 Sep 2013 12:45:21 GMT

I follow the lab's sampling instructions. Idexx still request samples in boric acid so they get samples in boric acid.

If they request them in a used, but well rinsed jam jar that is what they will get.

Re: Mismatching urinalysis results

David Mills — Mon, 30 Sep 2013 11:20:38 GMT

[quote user="Michael Woodhouse"]I'm all for evidence base - but don't believe on changing everything I do based on a single paper.[/quote]

Really? Well, unless you've a record of >250 samples, in a controlled retrospective study, that contradicts that study and supports your own view, I'm afraid you really should be changing your practice. Your objections are based merely on logistics, easily rectified, which to me seems very odd.

As for culturing free catch whether it's been collected on a Saturday or fresh out of the dog there and then, I wasn't aware anybody did this anymore given the high false positive rate?

"Evidence based medicine is OK as long as it doesn't interfere with my own dogma or makes me admit I may have been doing things sub-optimally"

Re: Mismatching urinalysis results

emma_j — Mon, 30 Sep 2013 11:07:07 GMT

That is interesting about the plain vs boric - hadn't come across that study before. This morning's urinalysis has duly been sent off with the courier sans boric, Iets see what happens! I always send both but if don't have enough sample to fill the boric, will tip the pot upside down first to empty out excess crystals, was told to do this by someone at idexx I think.

I don't consider c&s to be that expensive but I most commonly will order it as an add-on - I think about £17 gets chemistry, sediment, culture & pr:cr ratio if ordered at the same time as a blood screen.

Re: Mismatching urinalysis results

Kate Richardson — Mon, 30 Sep 2013 10:32:58 GMT

[quote user="David Mills"]

[quote user="Kate Richardson"]A recent study showed that you were actually more likely to get a false negative if you submitted samples in Boric acid- Idexx apparently participated in this study but their advice appears to contradict this study.[/quote]

Beat me to it!

[/quote]

Maybe Graham from Idexx could comment? It was another pathologist who I got the info from, not from Idexx, don't know which lab they worked at.

Re: Mismatching urinalysis results

John Flynn — Sun, 29 Sep 2013 16:54:35 GMT

[quote user="David Mills"]Anyone any idea why C/S is so damned expensive given the running costs are pretty low?[/quote]

Costs can be cut sizeably by sticking on some blood agar in an incubator and just posting plates that actually grow something.

Less false negatives also.

Re: Mismatching urinalysis results

Michael Woodhouse — Sun, 29 Sep 2013 16:07:04 GMT

We've discussed the study before. There are lots of urine samples a few days old before they get to the lab. See a dog Sat AM - send home with a pot. Collect Sat PM, drop to surg Mon AM, gets to lab Tue AM. Christmas post delaying things, bank holiday weekends. Suboptimal conditions (warm in summer time etc etc).

Equally just because you can grow bacteria at 2 hours and not at 24hours doesn't mean that that was significant. Perhaps a few contaminated bacteria grew on the 2 hour sample and not on the 24 hour sample?

I'm all for evidence base - but don't believe on changing everything I do based on a single paper.

Re: Mismatching urinalysis results

David Mills — Sun, 29 Sep 2013 15:50:29 GMT

Beat me to it!

Re: Mismatching urinalysis results

David Mills — Sun, 29 Sep 2013 15:49:13 GMT

[quote user="Michael Woodhouse"]Are you following your labs sampling protocol? Idexx want urine cultures in boric acid (red top universals) and I have spoken to them a few times and despite them giving the pots away FOC they tell me regularly ignored.[/quote]

There was a paper looking at this fairly recently (from Liverpool I think) and there was no difference between using plain sample pots and boric acid - in fact boric acid gave a higher false negative rate cf plain tubes. The pH of the urine can afefct how acidic the final boric acid/urine solution is which will affect the survivability of the bacteria - all too fiddly I think. So, to the OP, if you're using boric acid tubes, start using plain.

There are all sorts of reasons why bacturia doesn't yield positive culture. False positives esp under microscope are fairly common I think, low numbers of bacteria, bacteria sequestered within the bladder wall.

Anyone any idea why C/S is so damned expensive given the running costs are pretty low?

Re: Mismatching urinalysis results

Kate Richardson — Sun, 29 Sep 2013 15:42:52 GMT

[quote user="emma_j"]What are your thoughts when bacteria is seen on urine sediment (from a cysto or good clean sample) but a few days later the lab reports no growth on culture? Treat the culture as spurious and presumptively treat a UTI, or believe the culture and assume that there is no significant UTI?[/quote]

I think it depends hugely on the case in question as you then go on to say eg signs of cystitis or asymptomatic diabetic (as in no urinary tract signs) or dog/cat with chronic renal disease, but in general I would be looking for neutrophils as well. If I have a high clinical suspicion of bacterial infection then I would treat; if the animal is asymptomatic I would probably repeat the sample a week or so later.

A recent study showed that you were actually more likely to get a false negative if you submitted samples in Boric acid- Idexx apparently participated in this study but their advice appears to contradict this study. The conclusion was that postal urine samples should be submitted to the laboratory in a plain sterile tube. Personally I tend to stick a swab into the urine as well and send the swab with the sample.

The effect of boric acid on bacterial culture of canine and feline urine.
J Small Anim Pract. October 2011;52(10):510-4.
M Rowlands1; L Blackwood; A Mas; P Cripps; C Crompton; R Burrow
1Small Animal Teaching Hospital, University of Liverpool, Neston, Cheshire CH64 7TE.
© 2011 British Small Animal Veterinary Association.
Article Abstract

OBJECTIVE: To identify the optimal method of submission of canine and feline urine for bacterial culture.

METHODS: Cystocentesis samples from 250 animals (200 dogs, 50 cats) suspected of having urinary tract infections were collected. The reference aliquot, without preservative, was processed on site within 2 hours. Two further aliquots (one without preservative, one with boric acid) were stored at room temperature for up to 7 hours and then posted by guaranteed next day delivery to a commercial laboratory for analysis.

RESULTS: Forty-seven of the samples were positive on culture in the reference test. There was no significant difference between reference test results and those of samples posted without preservative (P=0·39), but samples posted in boric acid were significantly less likely to give a positive result (P=0·01). Samples posted without preservative had a sensitivity of 82% and a specificity of 98%; for boric acid, sensitivity was 73% and specificity 99%.

CLINICAL SIGNIFICANCE: Postal urine samples should be submitted to the laboratory in a plain sterile tube.

Re: Mismatching urinalysis results

Michael Woodhouse — Sun, 29 Sep 2013 14:33:57 GMT

The human medics recognise that you may find bacteria in the urine of 'normal' people - especially the elderly. It doesn't automatically require treatment.

Are you following your labs sampling protocol? Idexx want urine cultures in boric acid (red top universals) and I have spoken to them a few times and despite them giving the pots away FOC they tell me regularly ignored.

I will treat if symptomatic. I will treat if I get a nasty bug back. With some comprehensive screen they include urine culture and if no symptoms I don't always treat if they come back positive.

If I have a patient in front of me screaming UTI I would start abs before getting the culture back.

Re: Mismatching urinalysis results

Andrew Kent — Sun, 29 Sep 2013 13:45:28 GMT

Negative culture is not unusual especially if sitting in the post or delay in plating up the culture. If bacteria are seen on a cysto sample (I wouldn't trust free catch) and compatible clinical signs then i would treat.

Re: Mismatching urinalysis results

CatherineThomas — Sun, 29 Sep 2013 12:02:14 GMT

I'd check the bottle of stain or just use a fresh bottle as there could be contamination. I think I remember a pathologist telling me that bacteria from urine often aren't very stable and can be difficult to culture. So if everything else points to infection I would still treat with antibiotics. On the slide I would look for intracellular bacteria and I would consider pH.