BMJ  2007;334:473-476 (3 March), doi:10.1136/bmj.39098.744560.47

Practice

Cases in primary care laboratory medicine

Hyponatraemia and hypernatraemia: pitfalls in testing

W Stuart A Smellie, consultant1, A Heald, locum consultant2

1 Clinical Laboratory, General Hospital, Bishop Auckland DL14 6AD, 2 Department of Medicine, General Hospital

Correspondence to: W S A Smellie info@smellie.com

Disorders of salt and water balance are extremely common in primary care. In many cases the cause is apparent and the result is not life threatening, but doctors should be aware of warning signs that may point to serious progressive disorders so that these can be diagnosed and managed early

The first 150 words of the full text of this article appear below.

Introduction

Many situations involving the use and interpretation of laboratory tests are not supported by the high levels of evidence that can be achieved when interventions are assessed, but considerable consensus guidance is available on optimal use of laboratory tests. This article considers two scenarios involving salt and water balance that may be seen in primary care and discusses when further investigations may be helpful, and it gives a summary of evidence based and consensus guidance.


Summary points

Hyponatraemia is common in primary care; hypernatraemia is rarer
In both conditions, the common causes are usually clinically apparent
When great or rapid changes occur, consider rarer causes
Urine spot sodium concentration and osmolality help to differentiate the cause
Unexpected results should raise suspicion of pseudohyponatraemia and pseudohypernatraemia


Although disorders of salt and water balance are extremely common in primary care, their causes are usually apparent, and the primary clinical question that arises is whether . . . [Full text of this article]

Case 1

Case 2

Discussion

Questions and answers: learning points

Evidence note


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Rapid Responses:

Read all Rapid Responses

Urine tests are often unhelpful in diagnosis of hyponatraemia
Mat Davies
bmj.com, 7 Mar 2007 [Full text]
Re: Urine tests are often unhelpful in diagnosis of hyponatraemia
W Stuart A Smellie, et al.
bmj.com, 19 Mar 2007 [Full text]
hyperglycemia for raised serum osmolarity
weekitt kittisupamongkol
bmj.com, 10 Apr 2007 [Full text]
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