Tagg, A. Urine collection, Don't Forget the Bubbles, 2017. Available at:
Urine, the other amber nectar, is something we seem to want to check in nearly every unwell appearing child. But what do you do if they just don’t want to go? You’ve filled them up with icy poles or dilute apple juice and you are just waiting for a sample to be produced. As a doctor (and as a parent) I have been urinated on (by children) more times than I dare to recall (in fact it happened to me just this morning) but how do we make sure we get a sample when we need it? With 4 hour targets to meet it’s worth considering any means of speeding up the process.
A positive urine culture is defined as a pure growth of > 104 colony forming units if via SPA or CSU
A positive urine culture is defined as a pure growth of > 108 colony forming units if via CCU or BSU
What’s so important about a clean catch anyway?
A diagnosis of urinary tract infection has downstream (pun intended) consequences so it is important to make sure any sample on which the diagnosis is made is as free from contaminants as possible. Whilst the gold standard technique is suprapubic aspiration (SPA) it is an invasive technique and so is often a means of last resort. Most studies comparing clean catch urines and SPA are small but show a high degree of clinical correlation. The National Institute for Health and Care Excellence (NICE) recommend using a clean catch sample as their preferred method but also allows for the use of collection pads.
Contaminated samples can lead to delays to diagnosis, repeated testing and administration of inappropriate antibiotics so it is important that if it is used, it is done properly. A study from the group at Monash in Melbourne looked to improve education for caregivers who were to collect the sample using a pre-made collection pack, complete with information handout but they found little change from pre-test levels (though this may have been related to a lower than normal pre-trial level of contamination).
So do we just watch and wait?
The standard clean catch technique is time consuming. Normally the perineum is thoroughly cleaned with sterile saline and the infant rested on a parents lap. If they are just given the usual yellow topped urine specimen jar the child will invariably wee as soon as mum or dad look the other way so some advocate a sterile bowl to catch the sample in. Other methods have been tried such as urine bags or nappy pads but these do not yield the same quality results. Sterility of the peri-genital skin can be hard to achieve and maintain and so the clean catch rate if contamination is high (up to 26% or 1 in 4 cases).
Urine collection pads are an alternative for the less vigilant parent but they do run the risk of contamination with faecal or perineal flora thus nullifying the test. Reducing the pad’s contact time to 30 minutes coupled with an audible enuresis alarm might reduce the degree of contamination.
Bagged samples result from a bag that is taped to the perineum. A 1976 study found 22 of 26 samples were contaminated – there was a false positive rate of 50%!
Can we speed up the process?
Anyone who has changed a nappy knows that the mere act of wiping the perineum or genitalia seems to stimulate a fountain of urine, especially when you have just put a clean nappy on. Kaufman and colleagues used this bit of parental knowledge to try and speed up the urine delivery process. The technique they describe involves cleaning the genital region with saline soaked gauze for 10 seconds before performing gentle suprapubic massage for up to 5 minutes. In this feasibility study of 40 children, under 2 years of age, 30% (twelve kids) passed urine within 5 minutes. A randomized controlled trial is in the works.
An alternative non-invasive technique from Herreros Fernández et al.
Labrosse et al. has someone rapidly tap on the suprapubic region at a rate of 100 per minute for 30 seconds followed by lumbar paravertebral massage for a further 30 seconds. The user should alternate these two techniques until 5 minutes has elapsed or urine is produced. This method has been externally validated in a number of other institutions.
What if that doesn’t work?
Contamination rates for the more invasive techniques are much lower with a reported rate from 0 to 7% for SPA specimens and 9 to 23% for a catheter based specimen. It is difficult for us to know how uncomfortable these procedures are for the children and so appropriate analgesia should be provided. It has been suggested that SPA is more uncomfortable.
Suprapubic aspiration, the ‘gold standard’, can be a challenge to perform well and has one of the highest rates of failure. There are few contraindications – abdominal distension, a bleeding diathesis or massive organomegaly – and the procedure can be made much easier with use of bedside ultrasound. The neonatal bladder is an abdominal organ and so is readily seen with basic ultrasound skills. Blind insertion of a needle has a success rate of around 50%. This improves up to around 90% using this technology. Success is much more likely if the bladder is full and so the first task is to make sure there is actually a target to aim for.
How to… Suprapubic aspiration
- 23g needle (or smaller for a preemie)
- 3ml or 5ml syringe
- Specimen jar
- Skin prep
- Ultrasound scanner
- Sensible assistant
- Apply topical analgesia if possible
- Use oral sucrose in infants less than three months
- Assistant should hold the infant down with the legs together and extended
- Identify the site of entry (see below)
- Clean the skin with an alcohol swab (don’t use it for the genitalia)
- Insert the needle at right angles to the skin
- Do it quickly and firmly as if you are popping a balloon
- Insert the needle to the hub then aspirate as you withdraw
- Make sure you are ready to catch as soon as you undo the nappy – they always seem to wee as you are cleaning the area
- Do the SPA before anything else (cannula or LP) for the same reason
- You need at least 20mls in the bladder to get a reasonable target
Urethral catheterisation is certainly easier than an SPA and can be performed by nursing staff with a success rate (i.e. enough urine is collected) of near 100%. It is not reliant on the volume in the bladder, unlike an SPA, and has been shown to be less painful for the infant. There is an increased risk, however, of contamination.
The bottom line
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