Justice Stevens delivered the opinion of the Court.
In this case, we must decide whether a state hospital's performance of a diagnostic test to obtain evidence of a patient's criminal conduct for law enforcement purposes is an [p. 70] unreasonable search if the patient has not consented to the procedure. More narrowly, the question is whether the interest in using the threat of criminal sanctions to deter pregnant women from using cocaine can justify a departure from the general rule that an official nonconsensual search is unconstitutional if not authorized by a valid warrant.
I
In the fall of 1988, staff members at the public hospital operated in the city of Charleston by the Medical University of South Carolina (MUSC) became concerned about an apparent increase in the use of cocaine by patients who were receiving prenatal treatment. In response to this perceived increase, as of April 1989, MUSC began to order drug screens to be performed on urine samples from maternity patients who were suspected of using cocaine. If a patient tested positive, she was then referred by MUSC staff to the county substance abuse commission for counseling and treatment. However, despite the referrals, the incidence of cocaine use among the patients at MUSC did not appear to change.
Some four months later, Nurse Shirley Brown, the case manager for the MUSC obstetrics department, heard a news broadcast reporting that the police in Greenville, South Carolina, were arresting pregnant users of cocaine on the theory that such use harmed the fetus and was therefore child abuse. Nurse Brown discussed the story with MUSC's general counsel, Joseph C. Good, Jr., who then contacted [p. 71] Charleston Solicitor Charles Condon in order to offer MUSC's cooperation in prosecuting mothers whose children tested positive for drugs at birth.
The first three pages of Policy M–7 set forth the procedure to be followed by the hospital staff to "identify/assist pregnant patients suspected of drug abuse." Id., at A–53 to A–56. The first section, entitled the "Identification of Drug Abusers," provided that a patient should be tested for cocaine through a urine drug screen if she met one or more of nine criteria. It also stated that a chain of custody should [p. 72] be followed when obtaining and testing urine samples, presumably to make sure that the results could be used in subsequent criminal proceedings. The policy also provided for education and referral to a substance abuse clinic for patients who tested positive. Most important, it added the threat of law enforcement intervention that "provided the necessary 'leverage' to make the [p]olicy effective." Brief for Respondents 8. That threat was, as respondents candidly acknowledge, essential to the program's success in getting women into treatment and keeping them there.
The threat of law enforcement involvement was set forth in two protocols, the first dealing with the identification of drug use during pregnancy, and the second with identification of drug use after labor. Under the latter protocol, the police were to be notified without delay and the patient promptly arrested. Under the former, after the initial positive drug test, the police were to be notified (and the patient arrested) only if the patient tested positive for cocaine a second time or if she missed an appointment with a substance abuse counselor. In 1990, however, the policy was modified at the behest of the solicitor's office to give the patient who tested positive during labor, like the patient who tested positive during a prenatal care visit, an opportunity to avoid arrest by consenting to substance abuse treatment.