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Timing of Blood Tests for Medication Adequacy

When undergoing hormone replacement therapy (HRT) for gender transition or other medical purposes, monitoring hormone levels is crucial to ensure that medication dosages are effective and within the desired range. The timing of blood tests plays a pivotal role in accurately assessing hormone adequacy. The form of hormone administration must also be considered, including pills, patches, gels/creams/sprays, and injections.

The Importance of Monitoring Hormone Levels

Monitoring hormone levels serves several essential purposes:

  1. Effectiveness of Treatment: To determine if the prescribed medication is achieving the desired hormonal changes, whether it’s masculinisation, feminisation or androgenisation.
  2. Safety: It ensures that hormone levels are within a safe and healthy range, preventing potential side effects or complications.
  3. Adjustment of Dosage: If hormone levels are outside the target range, the goal is to adjust medication dosages accordingly to achieve optimal results.

Variations in Hormone Administration

1. Pills:

  • Pills are typically taken daily, providing a continuous, consistent release of hormones.
  • Blood tests can be performed at any time during the day when taking pills since hormone levels remain relatively stable throughout the day.

2. Patches:

  • Patches are usually worn for several days (e.g., 3 to 7 days) and provide a continuous release of hormones.
  • Blood tests can be conducted at any time during the patch-wearing period, as hormone levels remain steady.

3. Gels/Creams/Sprays:

  • These topical forms of hormone administration are applied daily and provide a consistent daily dose.
  • Blood tests can be performed at any time during the day when using gels, creams, or sprays.
  • Important: It’s essential to avoid taking blood from an area of skin recently in contact with gel, cream or spray. Contamination of the blood test may obtain an abnormally high result. Continue reading for further information.

4. Injections:

  • Injections, such as intramuscular or subcutaneous injections, deliver a bolus of hormones and create peaks and troughs in hormone levels.
  • To assess the trough levels (the lowest point in the hormone cycle), blood tests should be conducted just before the next injection is due. This timing provides the most accurate representation of the hormone’s lowest concentration, ensuring safety and efficacy.

Timing Blood Tests for Injections

For individuals receiving hormone therapy via injections, timing blood tests to coincide with the trough levels is crucial. Here’s how it works:

  1. Frequency of Injections: Determine the frequency of injections, which could be weekly, bi-weekly, monthly, or three-monthly depending on the medication prescribed.
  2. Trough Levels: Aim to schedule blood tests just before the next injection is due. This timing captures the hormone’s lowest concentration, ensuring that it remains within the desired range throughout the entire dosing interval.
  3. Consultation: Consult with a specialist to establish the ideal timing for your blood tests based on the specific medication, dosage, and injection schedule.

Do I need to fast before my blood test?

Whether you need to fast before a blood test for gender-affirming care depends on the specific tests you are having. Some blood tests do require fasting, while others do not. Here are some general guidelines:

1. Hormone Level Testing: Hormone level tests, such as those for testosterone or estrogen, do not require fasting. You can have these tests done at any time during the day.

2. Liver and Kidney Tests: These tests do not require fasting, You can have these tests done at any time during the day.

2. Haematocrit: This test does not require fasting, You can have this test done at any time during the day. This test is included in the Full Blood Count.

3. Lipid Profile: Lipid profiles, which measure cholesterol levels, typically require fasting for 9-12 hours before the test.

4. Glucose Testing: If you’re having a fasting blood glucose test, you will need to fast for at least 8-12 hours before the test to get accurate results.

Contamination with Gels

Contamination is a significant concern when it comes to blood testing, particularly for people using hormone gels or creams as part of their hormone therapy regimen. It’s important to ensure that blood tests are conducted away from the site where hormone gel or cream is applied to prevent any potential interference with test results. Hormone gels and creams can contain active ingredients that may be absorbed through the skin and could potentially contaminate the blood sample if testing is done too soon after application.

Top Tips:

  • To reduce the risk of contamination, individuals should wait a minimum of four to six hours after applying hormone gel or cream before having blood drawn.
  • Use a different site to apply the gel, away from the blood test site.
  • In the days before a finger prick blood test, consider the possibility of using one hand for administering medication and the other for drawing blood. Additionally, wearing a non-absorbent plastic glove to apply medication may help keep skin clear. 
  • Blood tests by healthcare staff will typically be taken from the arm. 


Monitoring hormone levels is an integral part of hormone replacement therapy, ensuring that treatment is effective, safe, and tailored to individual needs. The timing of blood tests varies depending on the form of hormone administration, with injections requiring specific attention to trough levels. Collaborate closely with specialists to establish a testing schedule that aligns with your medication and treatment goals, ultimately maximising the benefits of hormone therapy while minimising potential risks.

Further Reading


Updated on April 3, 2024

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