Letters

Suprapubic aspiration in children Pyuria is a poor predictor of infection

It is the policy of our department to discourage requests for urine microscopy by clinicians wishing to diagnose urinary tract infection, though not for other purposes such as assessing renal disease.² We believe that microscopic examination is rarely useful in uncomplicated urinary tract infection. As this study shows, the presence of pus cells does not predict infection. If the decision to treat urinary infection is made on the basis of pyuria, many patients will receive unnecessary antibiotics, and treatment would be delayed in other, infected patients (nearly half in this study) while the results of culture are awaited. Another study has shown better results when urinary bacteria were examined microscopically. However, the level of bacteriuria (>10⁷ bacteria/ml) detected with this method means that many of the infected samples reported by Buys and colleagues would be missed. We recommend that the diagnosis of urinary tract infection should be made on the results of bacterial culture of a carefully collected specimen, and that the decision to treat be based on clinical grounds rather than the detection of pyuria.

R P Bendall, A P R Wilson

University College London Hospitals, London WC1E 6DB

1. Buys H, Pead L, Hallett R, Maskell R. Suprapubic aspiration under ultrasound guidance in children with fever of undiagnosed cause. BMJ 1994;308:690-2. (12 March.) [Abstract/Free Full Text]
2. Mond NC, Gruneberg RN, Smellie JM. Study of childhood urinary tract infection in general practice. BMJ 1970;i:602-5.
3. Vickers D, Ahmad T, Coulthard MG. Diagnosis of urinary tract infection in children: fresh urine microscopy or culture. Lancet 1991;338:767-70. [Medline]

Use of ultrasound guidance unclear

EDITOR, - Heloise Buys and colleagues reported performing ultrasound guided suprapubic aspiration in children with non-specific febrile illness.¹ I was intrigued that "suprapubic aspiration was uniformly successful, and no ill effects were seen" and by the term ultrasound guidance. It was not clear whether ultrasound was used merely to identify the presence of a full bladder and the best approach for aspiration or whether real time ultrasound guidance was used to visualise the bladder puncture and needle tip. The second technique is much more difficult and requires a degree of skill in using ultrasound techniques. It is also not clear whether attempts were made at aspiration if the bladder was seen but not full. If this were so, contamination of the urine specimen by bowel luminal contents may have accounted for some of the "bacteriuria" noted. Loops of bowel frequently overlie the bladder when it is not fully distended, and they may have been punctured. Therefore, was the aspiration uniformly successful?

N B Wright

Royal Liverpool Children's NHS Trust, Alder Hey, Liverpool L12 2AP

1. Buys H, Pead L, Hallett R, Maskell R. Suprapubic aspiration under ultrasound guidance in children with fever of undiagnosed cause. BMJ 1994;308:690-2. (12 March.)

Authors' reply

EDITOR, - The ultrasound equipment and techniques used in suprapubic aspiration are not sophisticated. We use an ATL Mark 100 with a 5 MHz probe, made redundant for diagnostic use by our imaging department on purchase of a more modern machine. Ultrasound is used to show the presence of urine in the bladder, and direct needle aspiration is carried out when urine in the bladder is clearly seen. Visualisation of the needle tip is not attempted.

The technique used is as described by O'Callaghan and McDougall.¹ They found that when the bladder of neonates was shown to contain urine, suprapubic aspiration was successful on first attempt in all cases, but without prior scanning urine was obtained in only 36% of first attempts. They also noted that the techniques can be taught to resident medical staff in less than 10 minutes. Our experience has been similar.

None of the cultures obtained suggested bowel contamination. Even when low bacterial counts are obtained on suprapubic aspiration, subsequent radiological investigation may reveal abnormalities.

H Buys, L Pead, R Maskell 

Paediatric Department, St Mary's Hospital, Portsmouth PO3 6AD.

1. O'Callaghan C, McDougall PN. Successful suprapubic aspiration of urine. Arch Dis Child 1987;62:1072-3. [Abstract]

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