Should I undergo an overnight sleep study (polysomnography) to evaluate obstructive sleep apnea as a cause of my elevated hemoglobin and hematocrit?

Should You Undergo Sleep Study for Elevated Hemoglobin/Hematocrit to Rule Out OSA?

Elevated hemoglobin and hematocrit alone are not sufficient indications for sleep testing, because obstructive sleep apnea rarely causes clinically significant polycythemia—occurring in only 1-6% of OSA patients—and sleep studies should be ordered based on clinical symptoms and signs of OSA, not isolated laboratory abnormalities. 1, 2, 3

When Sleep Testing Is Indicated Based on Clinical Features

Sleep testing (polysomnography or home sleep apnea testing) is appropriate when you have clinical suspicion of OSA, defined by the American Academy of Sleep Medicine as: 4, 5

• Excessive daytime sleepiness (the primary symptom)
• Plus at least two of the following:
  • Habitual loud snoring
  • Witnessed apneas, gasping, or choking during sleep
  • Diagnosed hypertension

Additional symptoms that support testing include unrefreshing sleep, daytime fatigue, impaired concentration, and chronic morning headaches. 6, 5

The Evidence Against Using Elevated Hgb/Hct as a Primary Indication

The relationship between OSA and polycythemia is weak and clinically insignificant in most patients:

• A 2017 study of 1,604 veterans found that only 1.6% had clinical erythrocytosis despite 77.4% having OSA, and OSA severity (apnea-hypopnea index) was not associated with hematocrit or erythrocytosis. 1

• A 2022 meta-analysis of 3,654 patients showed polycythemia prevalence of only 2% overall (2% in mild-moderate OSA, 6% in severe OSA). 2

• A 2015 Turkish study of 335 OSA patients found only 0.3% had clinically significant polycythemia. 3

What actually predicts elevated hematocrit is nocturnal hypoxemia, not OSA per se:

• Awake oxygen saturation and mean nocturnal oxygen saturation are inversely correlated with hematocrit, while apnea-hypopnea index is not. 1, 7, 8

• Other factors more strongly associated with elevated hematocrit include active tobacco use, increased alcohol consumption, and exogenous testosterone therapy. 1

The Diagnostic Pathway When Both Elevated Hgb/Hct and OSA Symptoms Are Present

If you have both elevated hemoglobin/hematocrit AND clinical symptoms of OSA, then proceed with sleep testing according to this algorithm: 4, 5

Step 1: Determine if you meet criteria for home sleep apnea testing (HSAT) versus in-laboratory polysomnography (PSG)

You must undergo in-laboratory PSG (not HSAT) if you have any of the following: 4, 5

• Significant cardiorespiratory disease (heart failure, coronary artery disease, COPD, pulmonary hypertension)
• Chronic opioid medication use
• History of stroke
• Neuromuscular disorders that could impair respiratory muscles
• Awake hypoventilation or suspected sleep-related hypoventilation
• Severe insomnia
• Suspected central sleep apnea or other sleep disorders

HSAT is acceptable only if you are "uncomplicated"—meaning you have high pre-test probability of moderate-to-severe OSA without any of the above exclusion criteria. 4, 5

Step 2: If HSAT is performed and results are negative, inconclusive, or technically inadequate

You must proceed to in-laboratory PSG because HSAT systematically underestimates OSA severity (it cannot measure true sleep time or detect hypopneas with arousals alone). 4, 5

The Role of Nocturnal Oximetry in Evaluating Unexplained Polycythemia

If you have elevated hemoglobin/hematocrit without clear OSA symptoms, nocturnal oximetry may provide diagnostic utility before committing to full polysomnography: 1, 7

• Mean nocturnal oxygen saturation is an independent predictor of polycythemia, more so than apnea-hypopnea index. 7

• In young men with OSA, hemoglobin ≥155.5 g/L and hematocrit ≥44.6% had diagnostic utility for assessing nocturnal hypoxemia severity. 7

• However, overnight oximetry alone is insufficient for OSA diagnosis—the AASM explicitly advises against using oximetry without flow or effort signals. 5

Critical Pitfall: Do Not Assume OSA Is the Cause of Polycythemia

When polycythemia is present, you must exclude primary polycythemia vera (PV) through JAK2 mutation testing and erythropoietin levels, even if OSA is documented: 9

• OSA can mask the diagnosis of polycythemia vera by providing a presumed "secondary" explanation for elevated counts. 9

• The 2016 WHO criteria for polycythemia vera require JAK2 mutation or bone marrow findings plus low erythropoietin levels. 9

• Do not attribute polycythemia to OSA without first excluding PV, especially if the degree of polycythemia is disproportionate to the severity of nocturnal hypoxemia. 9

Bottom Line Algorithm

For isolated elevated Hgb/Hct without OSA symptoms:

• Do not order sleep testing based on laboratory values alone 1, 2, 3
• Evaluate for other causes: smoking, testosterone therapy, alcohol use, chronic lung disease, renal disease, and polycythemia vera 1, 9
• Consider nocturnal oximetry if unexplained nocturnal hypoxemia is suspected 1, 7

For elevated Hgb/Hct with clinical OSA symptoms (excessive sleepiness plus ≥2 of snoring/witnessed apneas/hypertension):

• Order sleep testing based on the clinical symptoms, not the laboratory abnormality 4, 5
• Choose PSG over HSAT if any exclusion criteria are present 4, 5
• If HSAT is negative or inconclusive, proceed to PSG 4, 5

For confirmed polycythemia (not just borderline elevation):

• Always screen for polycythemia vera with JAK2 mutation and erythropoietin level before attributing it to OSA 9
• If OSA is confirmed and treated with CPAP, hemoglobin typically decreases by only 3.76 g/L—insufficient to normalize true polycythemia 2