01/07/2008 AT 06:00 AM EST
tested free of illegal drugs and alcohol during her two-night stay at Cedars-Sinai Medical Center, a reliable source tells PEOPLE.
"She tested clean," the source says. "This lady is as clean as clean can be, and has been for some time."
The source adds the pop star never threatened suicide during the four-hour standoff at her Studio City home Jan. 3, saying such rumors were "bull----."
Spears, 26, was hospitalized early the morning of Jan. 4 under California's "5150 Hold," in which she was deemed a danger to herself or others and could be held for 72 hours for evaluation. Based on officers' observations at the scene, police said she appeared to be "under the influence of an unknown substance."
Two separate sources who are acquaintances of the family tell PEOPLE they believe the singer has an undiagnosed bipolar disorder.
One of those sources says Spears has "suffered from a psychological disease for years."
Spears left the hospital on Saturday, well before the 72 hours. Patients can be released early if doctors determine they no longer require treatment or evaluation.
"The 5150 legality is very loose," says Dr. Nathan Kuemmerle, a West Hollywood psychiatrist. "The 72 hours are not firm. All it requires is an ER psychiatrist to release the patient. ... If Britney isn't suicidal or homicidal, she doesn't need to be hospitalized."