A better way to collect urine samples?

Picture this… it’s a busy shift at work, like any other day. In cubicle five is a seven-month-old infant, with a fever in absence of respiratory or ENT systems. You knew the order was coming, the Doctor on duty is wanting a clean-catch urine sample. You know that there’s a supply of urine bags in the supply closet, so you let them know you’re heading over to apply one. “Not so fast,” the Doctor says, “I said a CLEAN catch urine sample, there’s risk of contaminates if you use the bag. And good luck keeping it on a hot, sweaty baby, they slide off and we haven’t got all day.” So, you’ve got a few choices in this situation.

  1. Put the urine bag on and hope it works, pretend that it was a clean catch
  2. Put a catheter in the baby or a needle into the bladder
  3. Use another technique to make sure that you get a midstream sample

But what is the 3rd technique? Hopefully, it’s less invasive than catheterising a teeny baby, and risking a UTI if they don’t already have one. Let alone the distress, both for the patient, the worried young parents, and you as the nurse. 

This article came about after reading this piece by Fernández et al., where they described a new technique for obtaining a clean-catch urine sample from a not yet continent child. More about that below, but first, let us look into some of the other ways traditionally used for obtaining urine.

Wee wee wee – why do we like using urine bags for obtaining urine samples?

I shared something relating to clean-catch urine techniques on Twitter recently and a non-nursing acquaintance commented that it had taken several attempts for her family to get a clean-catch sample from her young infant and there was a lot of urine everywhere. Urine bags might make us feel better as nurses because they allow us to complete other tasks while we wait for the urine sample (which let’s face it, might be a while in the case of a dehydrated child). Urine bags allow children too young to express their need to void, a way to catch a urine sample.

They are also a less messy way to catch urine, and may reduce staff time. In some outpatient areas Doctors may also allow families to return home and drop in a urine sample later if they are on the lower-risk end of the spectrum.

So if we think in terms of patient (or maybe more family) centered outcome, earlier discharge might be a good thing, no one likes sitting in a clinic for hours with a grumpy baby.

What is the evidence against urine bag use for collecting urine samples?

This brings us to the reasons why urine bags might not be so great. Firstly, let’s explore the success rate in catching enough urine for a dipstick or culture.  A study in 2012 by Tosif, Baker, Oakley, Donath & Babl explored this and compared the rates of contamination between the different urine sample collection methods. For urine bags they found contamination rates in their study the rate were 43.9%, which is concerning as this can cause inappropriate treatment where true infection is not present. However, clean catch urine samples on the other hand only had a prevalence of 14.1%, which coincidently was the same as catheter samples, but more than suprapubic aspirates at 9.1%. 

RCH has gone as far as not recommending urine bags for catching urine for possible urinary tract infections as they state the contamination rate can be as high as 50% (The Royal Children’s Hospital Melbourne, 2019). Their use in cases where we need urine for non-infective testing is permitted according to their parent advise fact-sheet which is available here.

Correct urine bag use is tricky

Urine bags can be fiddly, and slippage can happen for a few reasons, we can break these issues down into staff error, patient factors and anatomical reasons.

Putting on a urine bag is a skill just like any other nursing task. We need to ensure that staff are trained well in order to make sure the urine bag is best placed to catch urine. Common mistakes include being placed too low or too high, or wrong way roundPatient factors can include the amount of sweat, skin temperature or amount of distress during and post-application. Thirdly there’s the anatomical reasons, namely that it’s easier to apply a urine bag on males. Anecdotally I’ve found there’s a much higher failure rate on females, due to the needing to correctly secure on the labia. On males, the bag can fully enclose the scrotum and penis.

Other collection methods

There are other ways to collect urine samples in the infant, but they can come with more staff time, distress, risk of infection and cost. One method would be a simple catheter inserted, which is fine if there’s someone who feels confident in doing them. But they come with a risk of iatrogenic infection and the process is upsetting to the patient and sometimes family. There is a lower risk of contamination compared to urine bags, of 14.3% (Tosif, Baker, Oakley, Donath & Babl, 2012).

The other slightly more evasive method would be the suprapubic aspirate. Put simply, this involves inserting a needle into the child’s bladder and pulling out some urine. This might be a slightly harder sell to parents, requires a confident and competent practitioner and ideally the availability of ultrasound. The rate of contamination in the study cited above was 9.1% (Tosif, Baker, Oakley, Donath & Babl, 2012). This was the lowest prevalence found, but we need to weight up the risks and benefits of undertaking such a procedure.

The research

The Fernández et al method involved two medical or nursing staff to obtain a sample. One to hold up the infant under the axilla, with legs dangling and one to capture the urine in the specimen cup. Their first step is to provide analgesia in the form of sucrose syrup or feeding. Then followed by tapping the suprapubic area for 30 seconds at a rate of 100bpm. For reference, the Australian Resus council recommends CPR is done at 100-120bmp, so think along those lines. Then massage the lower back in a circular motion at the paravertebral zone. In their study the mean time to produce urine was under one minute, which is quite impressive.

The RCH guidelines to non-evasive clean-catch urine collection are slightly different to the one by Fernández et al. In the RCH parent guideline, from the diagram it looks like you lie the infant on their back while you either 1. Just wait for a wee. Or 2. Try the trick with rubbing gauze soaked in cool water over the lower abdomen. With method number one you could be waiting a long time and risk the aforementioned wee-tsunami described above. This would have the advantage of not requiring two people to assist and distress to the infant of someone holding them upright. The RCH site states however, that even clean-catch can have a contamination rate of 25%, which is still significant, but far less than the 50% they state can occur with urine bag collection. 

Why this works:

For this let’s look back at some pathophysiology.

In adults, micturition is caused by a feedback loop, as the bladder fills with urine the bladder stretches. It is this stretch that causes the signals to the brain to create the feeling of needing to urinate. From there generally, we are able to choose at a convenient time to pass urine (in the case of nurses, we often hold on a bit longer than we should). However, in infants under two years of age, full bladder control by voluntary urination is not possible. One of the nerves responsible for bladder control, the pudendal nerve, responds involuntarily to an increase in abdominal pressure or bladder stimulation.

The development of urinary control does not usually occur till over 2-3 years of age (Tran et al., 2016). After that age, developmental and neurological changes occur which allow children to learn the process of being continent. Therefore, making it much easier to capture the elusive urine sample.

What are your thoughts? Have you tried this technique? When it comes to it, I always forget to try it out, but I’m trying to find an opportunity to try.

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