The HP short DST test, also known as the HP short dynamic signal test, is a diagnostic test used to assess adrenal function and reserve. It involves taking measurements of cortisol and ACTH levels at specific time points after the administration of a low dose of dexamethasone, a synthetic glucocorticoid. The test is “short” because samples are collected over a shorter time frame compared to the standard DST.
The HP short DST provides information about the function of the hypothalamic-pituitary-adrenal (HPA) axis, which plays a key role in managing stress and regulating various body processes. The HPA axis controls the production and release of cortisol, the main glucocorticoid hormone in humans.
Some key facts about the HP short DST:
- It is used to diagnose adrenal insufficiency or Addison’s disease.
- It assesses adrenal response to stimulation with ACTH.
- It involves overnight dexamethasone suppression followed by ACTH administration.
- Serum cortisol levels are measured at baseline and at intervals after ACTH dose.
- Normal response is cortisol increase of ≥7 μg/dL.
- Low or absent cortisol response indicates adrenal insufficiency.
Read on to learn more details about what the test involves, how to prepare, the procedure, results interpretation, accuracy, and limitations of the HP short DST.
What Does the Test Assess?
The main goal of the HP short DST is to evaluate the adrenal glands’ ability to produce cortisol in response to adrenocorticotropic hormone (ACTH) stimulation. ACTH is a hormone produced by the pituitary gland that signals the adrenal glands to release cortisol.
Specifically, the test assesses:
- The integrity of the HPA axis
- Pituitary function in terms of ACTH release
- Adrenal gland responsiveness and cortisol secretory capacity
- Adrenal enzyme activity involved in cortisol synthesis
It can help distinguish primary adrenal insufficiency (Addison’s disease) from secondary adrenal insufficiency caused by pituitary dysfunction. It is also used in the diagnosis of congenital adrenal hyperplasia (CAH).
When is the Test Ordered?
The HP short DST is typically ordered when adrenal insufficiency or hypofunction is suspected based on symptoms, but the diagnosis remains uncertain.
It is often done in the following clinical scenarios:
- To confirm suspected primary adrenal failure in cases of Addison’s disease
- To evaluate pituitary function in secondary adrenal insufficiency
- To distinguish between primary and secondary adrenal hypofunction
- As follow-up in patients undergoing steroid taper after prolonged glucocorticoid therapy
- To diagnose adrenal suppression from exogenous steroids
- To assess disorders of cortisol metabolism like CAH
- To evaluate adrenal reserve capacity in critically ill patients
The test should be ordered by an endocrinologist or other specialist when there is a strong clinical suspicion of adrenal dysfunction based on symptoms, history, and initial workup.
Preparation for the HP Short DST
No significant preparation is required for the HP short DST. However, these general guidelines should be followed:
- No need to fast for the test
- Inform the doctor about any medications being taken currently
- Individuals need to avoid taking glucocorticoids for some time prior to the test as it can interfere with results
- Timing of sample collection must be strictly followed
- Blood samples are usually collected via an IV line
- Hospitalization may be required for frequent overnight sampling
The main preparatory step is to stop exogenous steroids for 1-2 weeks before the test under medical supervision. Short-acting steroids may need to be avoided for only 1-3 days. Estrogens and spironolactone can also affect results.
Procedure of the Test
The HP short DST is done in the hospital or at a medical center equipped for frequent overnight blood sampling. The procedure takes place over 1-2 days.
Here are the key steps:
- An IV catheter is placed for easy blood draw.
- Baseline/pre-dexamethasone cortisol level is measured at 8-9 am.
- Low dose dexamethasone tablet (0.5mg) is ingested at 11 pm.
- Cortisol level is measured again at 8 am next morning.
- Synthetic ACTH is injected IV at 9 am.
- Cortisol levels are measured at 15-minute intervals for 1-2 hours after ACTH dose.
- Levels of other hormones like ACTH, renin, aldosterone may also be measured.
The dexamethasone dose acts to suppress any normal cortisol production from a functional HPA axis. The ACTH stimulus then evaluates the adrenal response to see if adequate cortisol can be produced on demand. This helps to pinpoint where exactly dysfunction or suppression is occurring along the HPA axis.
HP Short DST Results
Results of the HP short DST are based mainly on the cortisol response seen at intervals after synthetic ACTH administration. Interpretation of the test involves analyzing:
- Baseline morning (8 am) cortisol level
- Cortisol suppression overnight after dexamethasone
- Subsequent cortisol response to ACTH stimulation
Normal HP Short DST Results:
- Morning baseline cortisol: 5-25 μg/dL
- Cortisol suppression to < 1.8 μg/dL after dexamethasone
- Cortisol increase of ≥ 7 μg/dL from baseline following ACTH
Abnormal results may indicate:
- Primary adrenal insufficiency: Impaired response to ACTH stimulus due to adrenal hypofunction or disease. No cortisol rise despite high ACTH.
- Secondary adrenal insufficiency: Low baseline cortisol from pituitary ACTH deficiency. Inadequate cortisol response to ACTH administration.
- Tertiary adrenal insufficiency: Hypothalamic disease results in low ACTH and low cortisol at all timepoints.
- Medication-induced adrenal suppression: Dexamethasone fails to lower cortisol indicating impaired HPA axis due to exogenous steroids.
Detailed interpretation requires analyzing the cortisol pattern of response, the peak stimulated level achieved, and the overall change from baseline. Borderline or inconsistent results may warrant repeat testing.
Accuracy of the HP Short DST
When performed correctly, the HP short DST has a relatively high degree of accuracy for diagnosing adrenal insufficiency:
- Sensitivity is approximately 90-100% for detecting primary adrenal failure.
- Specificity is 80-90% for confirming adrenal hypofunction when using optimal interpretive criteria.
- Measurement of ACTH levels also improves diagnostic accuracy.
- A peak cortisol response < 18-20 μg/dL has highest accuracy for diagnosing adrenal insufficiency.
However, no test is perfect. Factors that can impact accuracy include improper technique, poor patient preparation, interfering medications, sample timing errors, and suboptimal interpretive criteria.
When performed correctly and interpreted properly, the HP short DST can accurately diagnose adrenal insufficiency in majority of cases and help distinguish primary versus secondary causes.
Limitations of the HP Short DST
While the HP short DST is useful for assessing adrenal function, some limitations should be considered:
- Not 100% sensitive or specific – misses some cases of subtle HPA axis dysfunction.
- Does not assess actual cortisol production rates.
- Acute illness, stress can transiently alter results.
- Inter-individual variability in cortisol responses.
- Poor reproducibility – values may vary day-to-day.
- Not ideal for diagnosing mild secondary adrenal insufficiency.
- Timing is critical – samples must adhere to strict protocol.
- Results can be impacted by factors like patient compliance with dexamethasone.
Clinical correlation is important. Patients with equivocal findings may need repeat or confirmatory testing with insulin-induced hypoglycemia, metyrapone stimulation, etc. The short dexamethasone suppression test without ACTH stimulation lacks specificity for diagnosing adrenal insufficiency.
In summary, the HP short DST is an important and useful test for evaluating adrenal function when performed properly. However, limitations in diagnostic accuracy and result variability mean the results should not be interpreted in isolation. Clinical context and additional testing may be needed to confirm diagnosis in some cases.
Conclusion
The HP short DST is an important dynamic test used to assess the HPA axis and adrenal function. It involves overnight dexamethasone suppression followed by measurement of cortisol response to exogenous ACTH administration.
Key benefits of the test include good diagnostic accuracy for primary adrenal insufficiency when properly performed and interpreted. It can also distinguish primary versus secondary adrenal failure. Limitations include suboptimal sensitivity for detecting mild dysfunction and susceptibility to invalid results if protocol and timing is not followed.
Overall, the HP short DST provides useful diagnostic and functional information about the adrenal glands and HPA axis when used in the appropriate clinical context. However, the complexity of the protocol means it should be performed by specialty centers with expertise in dynamic endocrine testing. Results require careful interpretation and correlation with clinical findings to confirm or rule out adrenal disease.
