The complexity of diagnosing postural orthostatic tachycardia syndrome: influence of the diurnal variability

• We evaluated how the diagnosis can be missed in a single orthostatic stress test.
• Orthostatic tachycardia is more prominent in the morning, but not always.
• Symptoms were more frequent in the morning, but not during most tests.
• Orthostatic hypotension can be accompanied in postural orthostatic tachycardia syndrome.
• We suggest repeated orthostatic stress tests in clinically suspected postural orthostatic tachycardia syndrome patients.

We investigated how the diagnosis of postural orthostatic tachycardia syndrome (POTS) would be changed due to diurnal variability in orthostatic tachycardia. The orthostatic vital sign test was administered to each patient twice, in the afternoon of the day of admission and the next morning (n = 113). Forty-six patients were diagnosed with POTS, and the remaining 67 patients were assigned to non-POTS group. Heart rate increments after standing were larger in the morning than in the afternoon in every group (all P < .001). Among the POTS patients, 82.6% fulfilled the diagnostic criteria for POTS in the morning and 52.2% in the afternoon. Most POTS group (65.2%) displayed normal result on single orthostatic vital sign test. Orthostatic intolerance symptoms were provoked in only 45.7% of the POTS patients, more frequently in the morning. In conclusion, diurnal variability in hemodynamic parameters and provoked symptoms significantly challenged the diagnosis of POTS.