best tests September 2011 Sodium and Potassium Imbalance Quiz Feedback: Serum Protein Bands, bpac nz Testing During Pregnancy better medicin e Editor-in-chief We would like to acknowledge the following people Professor Murray Tilyard for their guidance and expertise in developing this edition: Editor Rebecca Harris Dr Sisira Jayathissa, Wellington Dr Cam Kyle, Auckland Best Tests Publication Manager Rachael Clarke Dr Hywel Lloyd, GP reviewer, Dunedin Dr Neil Whittaker, GP reviewer, Nelson Programme Development Team Mark Caswell Peter Ellison Julie Knight Noni Richards Dr AnneMarie Tangney Dr Sharyn Willis Dave Woods Best Tests is published and owned by bpacnz Ltd Report Development Justine Broadley Bpacnz Ltd is an independent organisation that promotes health Tim Powell care interventions which meet patients’ needs and are evidence based, cost effective and suitable for the New Zealand context. Design Michael Crawford Bpacnz Ltd has five shareholders: Procare Health, South Link Health, IPAC, Pegasus Health and the University of Otago. Web Gordon Smith Bpacnz Ltd is currently funded through contracts with PHARMAC and DHBNZ. Management and Administration Jaala Baldwin Kaye Baldwin Tony Fraser SOUTH LINK HEALTH Kyla Letman Clinical Advisory Group Clive Cannons Michele Cray Margaret Gibbs Dr Rosemary Ikram Dr Cam Kyle Dr Chris Leathart Dr Lynn McBain Contact us: Janet MacKay Mail: P.O. Box 6032, Dunedin Janet Maloney-Moni Email: [email protected] Dr Peter Moodie Free-fax: 0800 27 22 69 Stewart Pye Associate Professor Jim Reid Associate Professor David Reith www.bpac.org.nz Professor Murray Tilyard The information in this publication is specifically designed to address conditions and requirements in New Zealand and no other country. BPAC NZ Limited assumes no responsibility for action or inaction by any other party based on the information found in this publication and readers are urged to seek appropriate professional advice before taking any steps in reliance on this information. CONTENTS 2 A primary care approach to sodium and potassium imbalance Interpreting and managing a laboratory result of abnormal sodium or potassium levels is a common scenario in general practice. Electrolyte imbalances are more common in older people and in people with co- morbidities. The immediate cause of the imbalance is usually clinically apparent, e.g. fluid overload or depletion. In many cases medicines are implicated as a contributing cause. Indications for urgent referral to secondary care are detailed, and potential causes of the imbalance are discussed. 15 Quiz feedback: serum protein bands and routine laboratory testing during pregnancy Feedback from the results of the Best Tests July, 2011 quiz, which focused on making sense of serum protein bands and routine laboratory testing during pregnancy. best tests | September 2011 | 1 A primary care approach to sodium and potassium imbalance Interpreting and managing a laboratory result of abnormal sodium or potassium levels is a common scenario in general practice. The following series is a guide to the evaluation of abnormal sodium and potassium levels. Treatment of the electrolyte imbalance or the causes is not covered. 2 | September 2011 | best tests Serum sodium imbalance Understanding sodium imbalance Sodium is essential in the human body. It has a vital role In people with normal renal function and adequate in maintaining the concentration and volume of the aldosterone production, fluid and electrolyte balance extracellular fluid and accounts for most of the osmotic is able to be maintained in the body through these activity of plasma. Serum sodium levels are maintained by compensation processes. Sodium imbalances can indicate feedback loops involving the kidneys, adrenal glands and the presence of an underlying medical condition or the hypothalamus. affect of a medicine. When serum sodium is low (usually because total body Elderly people are more susceptible to sodium imbalances water is high), antidiuretic hormone (ADH) is suppressed due to age-related decrease or decline in:1 and a dilute urine is excreted.1 In addition, the kidney ■ Total body water produces renin, which stimulates aldosterone production, ■ Thirst mechanism which decreases the excretion of sodium in the urine, therefore increasing sodium levels in the body. ■ Maximal urinary concentrating ability ■ Ability to excrete water load When serum sodium is high (usually because total body ■ Renal function water is low), ADH is released, causing the kidneys to conserve water and therefore a concentrated urine is excreted.1 In addition, atrial natriuretic peptide (ANP) is Elderly people also commonly have multiple co- secreted by the heart (in response to high blood pressure morbidities that can affect sodium levels and renal caused by increased sodium levels) and promotes loss of function. In addition, use of medicines that affect sodium by the kidney (by inhibiting renin and therefore electrolyte excretion or retention, e.g. diuretics, also aldosterone secretion). commonly causes sodium imbalance.1 Key concepts: decreasing or increasing levels, if neurological symptoms are present or if the patient is ■ Serum sodium imbalances are more prevalent systemically unwell in older people and hyponatraemia is more ■ Further laboratory investigations may be commonly seen in general practice than appropriate if the clinical assessment and hypernatraemia patient history do not reveal the cause of the ■ The cause of the sodium imbalance is usually sodium imbalance clinically apparent, e.g. fluid depletion or overload The normal reference range for serum ■ Urgent referral to secondary care is sodium for adults is 135 – 145 mmol/L recommended for patients with serum sodium < 120 mmol/L or > 150 mmol/L, rapidly best tests | September 2011 | 3 Low serum sodium levels – Hyponatraemia Severe (serum sodium < 120 mmol/L) or rapid-onset Hyponatraemia is defined as a serum sodium hyponatraemia can be associated with disorientation, concentration < 135 mmol/L agitation, unsteadiness, seizures, coma and death, due to cerebral oedema.1, 2 Severe hyponatraemia is defined as a serum sodium concentration ≤ 120 mmol/L When hyponatraemia is associated with decreased extracellular fluid then signs and symptoms can Hyponatraemia is the most common electrolyte disorder include dizziness, postural hypotension and dry mucus and is often an incidental finding on routine blood tests. membranes. Hyponatraemia describes a serum sodium concentration Assessing a patient with hyponatraemia which is lower than normal (< 135 mmol/L). It is most commonly a result of excess water diluting the serum Assess the level of severity sodium levels in the body (e.g. as seen in congestive heart Refer the patient to secondary care for treatment if sodium failure), but hyponatraemia can also exist with normal or < 120 mmol/L. decreased water levels. Assess the trend Mild, asymptomatic hyponatraemia does not usually Check for previously low serum sodium measurements or require corrective measures except for treatment of the repeat the test if time permits. A rapid decrease in sodium underlying factors. Correction of hyponatraemia, when warrants referral to secondary care even if the actual required, is usually done in secondary care. Treatment degree of hyponatraemia is only moderate.3 must be gradual to avoid the risk of both fluid overload and cerebral demyelination, which can be fatal. N.B. changes of up to 5 mmol/L in two sequential individual results can reflect non-significant variation in sodium 3 Signs and symptoms of hyponatraemia levels. Signs and symptoms of hyponatraemia are generally Assess clinical status related to the underlying cause, whether or not it is Assess for signs and symptoms indicative of cerebral associated with fluid loss or dehydration, the degree of oedema, e.g. increasing confusion, decreasing hyponatraemia and the rate at which it develops. consciousness, seizures. If present, urgent transfer to hospital is indicated.3 The signs and symptoms of mild hyponatraemia are usually non-specific, e.g. nausea and lethargy. People with Assess if there is any acute illness, e.g. pneumonia, mild, long-term hyponatraemia are often asymptomatic.2 gastroenteritis. Medical disorders that can cause hyponatraemia Conditions that can cause hyponatraemia include: gastroenteritis, pneumonia, anorexia nervosa, renal disease, hypothyroidism, Addison’s disease, congestive heart failure, liver disease, myeloma, small cell lung cancer, lymphoma, stroke, tumour, meningitis.4, 5 4 | September 2011 | best tests Assess hydration status. Check for dehydration, postural changes in blood pressure, jugular venous pressure, Medicines that can cause hyponatraemia peripheral oedema and ascites. Ask about fluid intake/loss and increased/decreased thirst. Medicine-induced hyponatraemia usually develops within the first few weeks of starting treatment. Consider known conditions that may have caused the Once the medicine is stopped, the hyponatraemia hyponatraemia, e.g. congestive heart failure, renal or liver will usually resolve within two weeks (levels can disease. then be rechecked).6 In many cases, a combination of medicines is responsible for the hyponatraemia Assess the medication history rather than just one implicated agent. Look for medicines usually implicated in hyponatraemia, e.g. diuretics, selective serotonin reuptake inhibitors Diuretics cause hyponatraemia in approximately (SSRIs). 20% of people who take them,7 although severe hyponatraemia is nearly always seen with