Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

Nocturnal home oximetry was a sensitive but not specific test for identifying patients with the sleep apnea-hypopnea syndrome

ACP J Club. 1994 May-June;120:77. doi:10.7326/ACPJC-1994-120-3-077


Source Citation

Sériès F, Marc I, Cormier Y, La Forge J. Utility of nocturnal home oximetry for case finding in patients with suspected sleep apnea hypopnea syndrome. Ann Intern Med. 1993 Sep 15;119:449-53.


Abstract

Objective

To determine the utility of nocturnal home oximetry for case finding in patients clinically suspected of having the sleep apnea-hypopnea syndrome (SAHS).

Design

Blinded comparison of nocturnal home oximetry and polysomnographic nocturnal findings.

Setting

Sleep clinic of a tertiary referral center in Canada.

Patients

240 consecutive outpatients (age range 24 to 68 y, 90% men) referred for clinically suspected SAHS. Symptoms included loud snoring, nocturnal choking and awakenings or apneic events reported by a bedmate, bad sleep quality, and daytime hypersomnolence. None of the patients had previously been investigated by home or sleep laboratory recordings.

Description of test and diagnostic standard

All patients had a conventional polysomnographic study after nocturnal home oximetry, which was interpreted independently. Home oximetry was classified as abnormal (suspicion of sleep-related breathing abnormalities) in the presence of repetitive episodes of transient desaturation followed by rapid returns to the baseline arterial oxyhemoglobin saturation level (no minimum decrease in saturation and no threshold were required). The diagnosis of SAHS was confirmed when the apnea plus hypopnea index obtained by the sleep polysomnographic study was > 10, the diagnostic standard.

Main outcome measures

Sensitivity, specificity, positive predictive value, and negative predictive value of home oximetry.

Main results

The diagnosis of SAHS was confirmed in 110 of the 240 patients studied. In this group, the mean apnea plus hypopnea index and the arousal index were 38.1/h and 36.8/h, respectively. Nocturnal home oximetry was abnormal in 176 patients (including 108 patients with SAHS and 68 without SAHS) and was normal in 64 patients (62 without SAHS and 2 with SAHS). The sensitivity, specificity, and likelihood ratios for nocturnal home oximetry testing based on a cutoff point of 10/h are shown in the Table. The positive predictive value was 61% and the negative predictive value was 97%.

Conclusion

Nocturnal home oximetry was sensitive but not specific for case finding in patients clinically suspected of having the sleep apnea-hypopnea syndrome.

Source of funding: In part, The Respiratory Health Network of Centres of Excellence of Canada.

For article reprint: Dr. F. Sériès, Unité de recherche, Centre de Pneumologie, Hôpital Laval, 2725 Chemin Sainte Foy, Sainte Foy, Québec, G1V 4G5, Canada. FAX 418-656-4762.


Table. Test characteristics of nocturnal home oximetry testing for detecting sleep apnea-hypopnea syndrome*

Cutoff point Sensitivity (95% CI) Specificity (CI) +LR -LR
10/h 98% (93.6 to 99.8) 48% (38.8 to 56.6) 1.88 0.04

*LRs defined in Glossary and calculated from data in article.


Commentary

History and physical examination have a limited role in the evaluation of patients with SAHS (1, 2); the evaluation requires polysomnography (PSG) to confirm the diagnosis and the efficacy of a trial of nasal, continuous positive airway pressure or other interventions (3, 4). PSG, done in a sleep laboratory, often costs more than $1000; nocturnal home oximetry costs between $100 to $200 and has the potential to identify patients with suspected SAHS who need further evaluation with PSG.

In this study, Sériès and colleagues used the presence of either of 2 patterns of desaturation—deep, repetitive oxygen desaturations or low-amplitude periodic fluctuations in oxygen saturation—as criteria for an abnormal nocturnal home oximetry study. Technical problems required repetition of the test in approximately 8% of patients. The reproducibility of the nocturnal home oximetry interpretation was shown to be 95% in a randomly selected subset of 60 recordings. The high sensitivity of 98.2% suggests that nocturnal home oximetry using qualitative criteria for an abnormal test could be used to rule out SAHS. The low specificity of 47.7% limits the ability of nocturnal home oximetry to rule in the diagnosis of SAHS.

If these results are confirmed, patients with a low probability of SAHS should have nocturnal home oximetry; if negative, no further testing is needed. If positive, then PSG should be done. Patients with a high probability of SAHS should have PSG (without nocturnal home oximetry) to confirm the diagnosis and evaluate the efficacy of treatment. If other investigators are able to replicate the sensitivity and specificity of these criteria in other settings, then nocturnal home oximetry may become a useful cost-effective method for selecting patients with suspected SAHS for PSG.

Marc Silverstein, MD
Mayo ClinicRochester, Minnesota, USA


References

1. Haponik EF, Smith PL, Meyers DA, Bleecker ER. Evaluation of sleep-disordered breathing. Is polysomnography necessary? Am J Med. 1984;77:671-7.

2. Viner S, Szalai JP, Hoffstein V. Are history and physical examination a good screening test for sleep apnea? Ann Intern Med. 1991;115:356-9.

3. Kales A, Vela-Bueno A, Kales JD. Sleep disorders: sleep apnea and narcolepsy. Ann Intern Med. 1987;106:434-43.

4. Kaplan J, Staats BA. Obstructive sleep apnea syndrome. Mayo Clin Proc. 1990;65:1087-94.