The Editorial Executive Committee welcomes letters, which should be less than 250 words. Before a decision to publish is made, letters which refer to a published article may be sent to the author for a response. Any letter may be sent to an expert for comment. When letters are published, they are usually accompanied in the same issue by their responses or comments. The Committee screens out discourteous, inaccurate or libellous statements. The letters are sub-edited before publication. Authors are required to declare any conflicts of interest. The Committee's decision on publication is final.

Letter to the editor

Editor, – I think there is an unintentional inaccuracy in the Summary of the article 'Managing drug-induced hyponatraemia in adults' (Aust Prescr 2003;26:114-7). The first sentence of the Summary states that 'drug-induced hyponatraemia occurs in approximately 5% of outpatients...' but the source for this statement seems to be the Introduction which merely states that: 'A Melbourne laboratory found hyponatraemia in 4.8% of 326 923 samples from ambulatory patients...'.

Obviously the Melbourne sample is not representative of the whole population of ambulatory patients, or outpatients, as implied by the statement in the Summary. It is only a sample of patients who merited a blood sample being sent to the laboratory. Presumably these patients were sick enough for their general practitioner to investigate (we could call them 'sick outpatients'), and there is no account taken of all the ambulatory patients who did not have samples taken ('well outpatients'). The proportion of 'sick outpatients' who have samples sent to a laboratory is very small, surely less than 10% of the whole and probably much less than that. The problem with the statement in the Summary is that it is likely to be cited (especially when it appears in an authoritative publication like Australian Prescriber) but quoted out of context and so could mislead. It is certain, surely, that the proportion of outpatients with hyponatraemia is much less than 5%. Frankly, I'd be surprised if it was more than 0.5%.

Stuart Baker
Pharmacist
Mortlake, Vic.

Authors' comments

Dr S. Fourlanos and Dr P. Greenberg, the authors of the article, comment:

We thank Mr Baker for drawing our attention to misinterpretation of the first sentence of the Summary.

We hope that other readers, like him, will have read in the Introduction the selection process for the patients referred to in the Summary.

We agree that the first sentence of the Summary should read: 'Hyponatraemia occurs in approximately 5% of ambulatory and 14% of admitted patients referred for blood tests by general practitioners'.

The prevalence of hyponatraemia in other non-admitted patients and in the broader community is also unknown to us.