Normal Reference Range and Blood Testing
In Australia, a blood test is a standard way to measure serum sodium levels, often included in an electrolyte panel. A harmonised reference interval, used by most pathology laboratories across the country, establishes the 'normal' range for sodium.
Interpreting your blood test results
- Normal Range: The established normal range for blood sodium is 135–145 mmol/L.
- Abnormal results: Results outside this range are flagged as high or low but do not automatically indicate a serious medical issue. A doctor will interpret these results alongside your overall health and medical history to make a diagnosis.
- Other tests: If an imbalance is detected, a doctor may order further tests, such as a urine sodium test, to help identify the cause.
Understanding High and Low Sodium Levels
An imbalance in blood sodium is typically more related to water balance than the absolute amount of salt consumed. The two main conditions are hypernatremia and hyponatremia.
Hypernatremia: High sodium levels
Hypernatremia occurs when blood sodium levels rise above 145 mmol/L. This is usually due to dehydration, which can be caused by various factors, leading to a higher concentration of sodium in the blood.
Common causes of hypernatremia
- Insufficient fluid intake
- Excessive water loss from severe vomiting, diarrhoea, or sweating
- Kidney disease
- Taking certain medications like diuretics or corticosteroids
Symptoms of hypernatremia Mild cases might be asymptomatic, but more severe imbalances can lead to:
- Excessive thirst
- Fatigue and confusion
- Muscle weakness and twitching
- In severe cases, seizures and coma
Hyponatremia: Low sodium levels
Hyponatremia is defined as a blood sodium level below 135 mmol/L and is often caused by an excess of water relative to sodium, or the body retaining too much fluid.
Common causes of hyponatremia
- Taking certain medications, including some antidepressants and diuretics
- Underlying conditions such as heart failure, kidney disease, or liver cirrhosis
- Severe vomiting and diarrhoea
- Excessive fluid intake, known as 'water intoxication'
Symptoms of hyponatremia Symptoms can be non-specific, with more severe cases causing:
- Nausea and headaches
- Confusion and lethargy
- In severe or rapid-onset cases, seizures, coma, and potentially death due to cerebral oedema
Dietary Guidelines for Maintaining Sodium Balance
The average Australian adult consumes almost double the recommended amount of sodium, primarily from processed foods. A healthy, balanced diet is key to managing sodium intake.
Comparison Table: High vs. Low Sodium Diet
| Feature | High Sodium Diet | Low Sodium Diet |
|---|---|---|
| Associated Health Risks | High blood pressure, heart disease, stroke, kidney disease | Rare, mainly affecting endurance athletes with excessive sweating and fluid intake |
| Primary Sources of Sodium | Processed and packaged foods, fast food, condiments, and added salt | Naturally occurring sodium in fresh, whole foods like fruits, vegetables, and unprocessed meats |
| Effect on Taste | Taste buds become accustomed to high salt levels | Taste buds can adapt to lower salt in a few weeks, allowing natural flavours to emerge |
| Daily Recommendations | Average Australian consumes around 3,600 mg/day | Healthy adults advised to consume no more than 2,000 mg/day |
| Food Label Check | Often exceeds 400 mg sodium per 100g | Aim for less than 120 mg sodium per 100g, or labelled 'low salt' |
Strategies for a lower sodium intake
To reduce sodium intake and maintain healthy levels, consider these tips:
- Read food labels: Always check the Nutrition Information Panel on packaged goods. Compare sodium content per 100g between similar products to choose the healthier option.
- Cook from scratch: Preparing meals from fresh ingredients allows you complete control over the amount of salt added.
- Use natural flavour enhancers: Opt for herbs, spices, garlic, chilli, and lemon juice instead of salt to season food.
- Reduce processed foods: As 75-80% of dietary sodium comes from processed foods, limiting items like processed meats, packet sauces, and takeaway food is crucial.
- Retrain your palate: Gradually reduce the salt you add to meals and you will find your tastebuds will adjust over time.
Conclusion
The normal range for blood sodium in Australia is a tightly regulated measure, with 135–145 mmol/L considered the standard reference interval used by local pathology laboratories. While minor fluctuations are common, consistent deviations from this range can indicate underlying health conditions. Most Australians consume nearly double the recommended dietary sodium, which is linked to increased risk of cardiovascular disease. By being mindful of dietary choices, particularly reducing the intake of processed foods, and opting for fresh, whole ingredients, individuals can help maintain healthy sodium levels. However, for those with abnormal blood sodium results, it is crucial to consult a healthcare professional for a comprehensive evaluation and personalised management plan.
Note: If you have concerns about your sodium intake or electrolyte balance, an Accredited Practising Dietitian can provide personalised, evidence-based advice. More information is also available from the Heart Foundation and other reliable health organisations. It's essential to not make significant dietary changes without consulting a doctor, especially if you have an existing health condition or are on medication.
