Get a Diagnosis: Additional Testing

Looking for a Neurologic Cause (Nervous System)

If the cardiac evaluation, including the EKG, does not show evidence of arrhythmia as a cause of syncope, evaluation for neurally-mediated syndromes is recommended if a diagnosis has not been already found.3

In the people with POTS, the neurologic exam of the muscles and sensation can be normal in 98% of the patients (Mayo Clinic experience).7

The neurologic disorders that result in fainting and orthostatic intolerance are due to a problem with the autonomic nervous system.

If the diagnosis cannot be made with the history, physical (including Standing BP/Pulse Test and EKG, it is recommended that further studies be done. Some recommend additional testing if the person has consistent orthostatic symptoms and the symptoms significantly interfere with their daily activities. They use the grading of 3 or 4 by symptoms.

If POTS is suspected, additional tests could include:
    •  24-hour urine for sodium (to check fluid status) Goal - 1500-2500 mL and sodium excretion of 170 mmol/24 hr.5,7
    •  Blood epinephrine and norepinephrine levels (lying, then after standing about 30 minutes)5,6. This could also include dopamine levels. This testing would be recommended in those the physician suspects may have the hyperadrenergic form of POTS.5
    •  Tests for the autonomic nervous system function would include thermoregulatory sweat test and tests for the composite autonomic severity score (CASS) which includes sudomotor, cardiovagal and adrenergic tests and the autonomic reflex screen7. Not everyone considers these necessary to diagnose POTS. Symptoms would suggest there is other autonomic nerve damage. The tests help confirm whether it is present. There is no direct treatment for it.

    •  Other tests: 24-hour holter to match heart rate changes to symptoms, Exercise testing to evaluate heart rate response to activity, ganglionic antibody.7

Additional testing like MRI of the head or EEG monitoring are usually not needed. However, it would be indicated if it was suspected that the person was having seizures and that it is not a true faint or orthostatic problem.3

Orthostatic Stress Tests to Diagnose Neurally-Mediated Cause of OI Symptoms

There are 3 ways to do orthostatic stress testing.4 These tests create a stress that would bring out a person,s orthostatic problem and their symptoms. The test is an "orthostatic stressor".

Tilt Table Test (HUT, TTT)

The head-upright tilt table test is the orthostatic stress test that is used most often now.2-4 Even though the test has become more easily available and used to evaluate fainting and orthostatic symptoms, it has not been "standardized"*.

The main clinical reason to do the HUT is to create the symptoms of orthostatic intolerance that the person gets, in a place where the BP, pulse and other information about the body can be measured. It is not enough to see changes in the blood pressure (BP) and pulse.4 The person must have orthostatic symptoms to say that the cause of the symptoms is from orthostatic intolerance.

Dr. Stewart notes that the drugs used to provoke reactions during the HUT can potentially change the patient's internal reaction. This raises a question about the results especially when testing for POTS or true dysautonomic/orthostatic hypotension.4

HUT is less accurate as a test for fainting (syncope).4 The results are not especially repeatable.

In adolescents - if 4 people who do not usually faint are tested, at least 1 of them will faint during the test.

If you take adolescents who do faint regularly - during the HUT, 1 of them will NOT faint.

When the HUT is done, the results of the test are valuable information but they have to be looked at with the other information about the person, the history and symptoms and clinical judgment.

For POTS and autonomic dysfunction - the HUT seem more reliable in producing the symptoms with the changes in BP and pulse.4

How long the test is done: The test runs from 15-45 minutes depending on what they are looking for. If they are looking to see if the person gets tachycardia (fast heart rate) when they stand up for 10 minutes, a 10-minute tilt would be enough. If they are want to see if the person has more than one orthostatic condition, like delayed orthostatic hypotension (AKA NMH) or delayed faint (reflex syncope) after standing a longer time, then the test should run longer, 45 minutes.


Other factors. part of the test results is the recording the patient symptoms during the test. It is important that the technicians and nurses involved in the test understand what symptoms occur with orthostatic intolerance. Some of the symptoms that may not be understood or recorded: difficulty breathing can be interpreted as hyperventilation caused by anxiety instead of part of the orthostatic process to be recorded; fine muscle twitching of the hands, around the eyes; tingling or funny feelings in the hands - which could be interpreted by staff as being due to prolonged position and not part of the dysautonomic process.1


*When a test is "standardized", it means that the professional associations have developed guidelines for how the test should be done, how long a person should lie down before the upright tilt, what drugs should or should not be used, how long the test should be done, what should be recorded and documented and what the results mean. This is done so that a test done with one device or at one clinic/hospital can be repeated at another and get pretty much the same results. This means the results can be compared between testing places. They can also be compared over time, if a test is done one year and repeated in 3 years, the results could be compared.


The main goal of standardizing tests is to know that any differences in the test results are more likely due to differences in the person/patient and not to the test device or how the test was done.

LBNP-research tool

LBNP is Lower Body Negative Pressure test.4 It was developed by the NASA scientists. It has been a research tool. It is a device that creates negative pressure around the legs, buttocks and lower abdomen. To the body, it creates changes that are like standing up. This was used for research about how space flight affects astronauts.

Other tests of the Autonomic System

Thermoregulatory Sweat Test (TST) or the quantitative sudomotor axon reflex test (QSART) = tests for the failure of the autonomic nervous system (sympathetic cholinergic system). They test the sweating response (sudomotor function).
(Be sure to check with your insurance company. Some have specific policies that cover this test for some conditions and not others. For example, Aetna's policy does not cover this test for POTS or Raynaud's.(Policy updated 1/13/2012. Access to Policy.

Sympathetic adrenergic system - test is the blood pressure response to a valsalva maneuver

Parasympathetic nervous system - heart rate variability with deep respiration and during Valsalva maneuver

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  1. Strickberger SA, Benson DW, Biaggioni I, Callans DJ, Cohen MI, Ellenbogen KA, et al. AHA/ACCF Scientific statement on the evaluation of syncope. Circulation. 2006;113:316–327
  2. Moya A, Sutton R, Ammirati F, Blanc JJ, Brignole M et al., Guidelines for the diagnosis and management of syncope (version 2009). European Heart Journal (2009); 30: 2631-2671.
  3. Brignole M. Diagnosis and Treatment of Syncope. Heart 2007: 93; 130-136. Article PDF
  4. Stewart JM, Medow MS, Alejos JC. Orthostatic Intolerance. Medscape article.
  5. Grubb BP. Postural tachycardia syndrome. Circulation. 2008;117:2814–2817. Abstract. Article PDF.
  6. Thieben MJ, Sandroni P, Sletten DM, et al. Postural orthostatic tachycardia syndrome: The Mayo Clinic experience. Mayo Clin Proc. 2007;82:308–313.
  7. Low PA, Sandroni P, Joyner and Shen W. Postural Tachycardia Syndrome (POTS). J Cardiovasc Electrophysiology 2009; 20:352-358.  Abstract.  Article PDF

Author: Kay E. Jewell, MD
Page Last Updated: June 22, 2012