On 4 November 2025, the Royal Free London trust's laboratory changed the required sample type for parathyroid hormone (PTH) measurement from serum (gold top tube) to EDTA plasma (lavender top tube).

Parathyroid hormone is an unstable hormone that can degrade in serum over time, after collection. Switching to EDTA plasma significantly increases the stability of the sample. This important change is being implemented to improve the accuracy and reliability of PTH measurements. 

The change will help to

• reduce the need for repeat blood draws due to degraded sample
• ensure better sample integrity, especially for samples collected in off-site clinics and GP practices or those with delayed transport
• align with recommendations for improving the accuracy of PTH measurement. 

For further details see the communication from the trust.