HNY Policy and Pathway Repository - York

Normal range for serum potassium - 3.5 – 5.3 mmol/L

Mild hyperkalaemia - 5.4 – 5.9

Moderate hyperkalaemia - 6.0 – 6.4

Severe hyperkalaemia - ≥6.5

This scale of severity is arbitrary and serves only as a guide - the severity is actually dependent on the impact on the patient.

Laboratory staff may telephone a high potassium result through to primary care. This does not automatically mean patients require admission to hospital (see guidance below). The clinical urgency of the situation is mainly dependent on three factors: The severity of the hyperkalaemia and the rate of change in potassium and any change in serum creatinine/eGFR. Rapid rises in potassium or significantly impaired renal function increase the likelihood of the need for hospital admission.

Significant changes are:

• a sudden (within 1 week) rise in potassium
• a >10% increase in serum creatinine or >10% decrease in eGFR

Why is the potassium elevated?

If the potassium is elevated in the presence of either normal kidney function or stable chronic kidney disease, consider the following explanations for a high potassium:

• Spurious hyperkalaemia
  • Haemolysis
    The laboratory will not report a K+ result if the sample is grossly haemolysed (K+ result will appear as NA with a comment stating haemolysed sample). The laboratory will report a numerical K+ result along with a cautionary comment if a sample is slightly haemolysed. At this level of haemolysis, the contribution to K+ measured in serum will be very small (~0.2 mmol/L). Haemolysis has various causes e.g. difficult sample collection, shaking of the tube etc.
  • EDTA contamination
    Collection of blood samples in reverse traffic light order, i.e., green topped tube first, then amber, lastly red, prevents EDTA contamination of the sample. Gross EDTA contamination is usually detected within the laboratory and the K+ result will be reported as NA with an appropriate comment.
  • Delay in centrifugation / receipt in lab If there has been a delay in processing the sample, K+ will move from the red blood cells into the serum and contribute to high K+ results. This effect is more pronounced at low temperatures and so there is increased incidence in winter. Serum samples for K+ should NEVER be refrigerated. It is useful for the labs to have the time the sample was taken written on the blood bottle and request form, to help detect when this effect may have occurred. The laboratory will usually comment on reports if they consider a delay in receipt many have contributed to high K+.
  • Abnormally high Red cell count / White cell count / Platelet count Patients with abnormally high red cell, white cell or platelet counts may have spurious hyperkalaemia. A repeat blood test should be obtained in a lithium heparin tube obtained and taken at the hospital phlebotomy service to remove any transport effects. Please contact the Duty Biochemist to discuss.
  • Secondary to a metabolic acidosis – serum bicarbonate is automatically added on to all potassium results greater than 6.0mmol/L in York and Scarborough hospitals.
• Causes of genuinely raised serum potassium
  • Medications – see below
  • Abnormal kidney function:
    • Acute Kidney Injury
    • Chronic Kidney Disease (usually stage 4/5)
  • Other causes
    • Increased intake – very unusual, except in dialysis patients
    • Redistribution
      • Diabetic ketoacidosis (before treatment)
      • Severe metabolic acidosis
      • Diabetic nephropathy (patients with longstanding diabetes and moderate renal impairment)
      • Trauma/burns
      • Rhabdomyolysis and/or tumour lysis syndrome
    • Decreased excretion
      • Hypoadrenalism/Mineralocorticoid deficiency

Medications

• ACE inhibitors
• Angiotensin-2 receptor antagonists
• Aldosterone antagonists e.g. spironolactone/eplerenone
• Potassium supplements
• Potassium sparing diuretics
• NSAIDS
• Trimethoprim 
• Heparin
• Ciclosporin
• Tacrolimus
• Ketoconazole
• Theophylline
• Digoxin
• Dietary eg LoSalt
• Herbal remedies

This list is not exhaustive but covers the majority of commonly implicated substances. When reviewing medication, consider the indication for it and the potential consequences of stopping it.

Arrangements for reporting raised potassium results

Duty Biochemist (9am-5pm) 01904 726366 or via 01904 726802, via switchboard out of hours

Working day 9-5
The duty biochemist will review all potassium results >5.8mmol/L Results >6.5mmol/L are always phoned through to the GP surgery. Results <6.5mmol/L may be rung through to the GP surgery, at the discretion of the biochemist.

Out of hours
All potassium results >6.5 are actioned immediately by the laboratory staff and usually are telephoned to the Out Of Hours (OOH) GP Service. Results between 5.8 and 6.5mmol/L will be reviewed by the duty biochemist at 9am the next morning. Results may be telephoned through to the GP in the morning, at their discretion.

Clinical features of hyperkalaemia

Do not offer patients with hyperkalaemia dietary advice. Except in end stage kidney disease, dietary restriction is rarely appropriate in the management of high potassium and may lead to inappropriate restriction of healthy food choices when diet is rarely the cause of the hyperkalaemia. It is important in End Stage Kidney Disease and these patients should be supervised by a renal dietitian, who can both identify potential sources of high potassium foods and ensure that nutritional needs are met.

Do not prescribe calcium resonium. It has no place in the acute or long-term management of hyperkalaemia. Other oral potassium exchange agents that have been approved by NICE (Patiromer and Zirconium) have a very specific role in long term management and are usually initiated in secondary care.

Management of abnormal Potassium levels

1. Check if the result is spurious
2. Consider causes of hyperkalaemia