The Royal College of Pathologists said the use of demand management tools by some laboratories was 'entirely reasonable' to stop inappropriate testing.
GPs had complained that test requests are being 'bounced back' by labs that suspect the tests are being used for screening.
A spokeswoman for the college said: 'The use of serum CA125 testing for ovarian cancer needs careful consideration given that it is an imperfect marker with a significant false positive and false negative rate.
'It should only be used as a first line test for diagnostic purposes in women presenting with symptoms as outlined in NICE guidance on ovarian cancer.'
She added that CA125 should not be used to screen asymptomatic women.
'The use of demand management tools, used by some laboratories, to minimise such inappropriate testing is entirely reasonable as inappropriate use of tumour marker tests can do more harm than good when used on the wrong patient.
'False reassurance as well as inappropriate referral or subsequent unnecessary investigations are the main drawbacks which can cause delays in correct diagnosis and unnecessary distress for patients. It is vital that individual laboratories work with GPs to ensure optimum use of the CA125 test.'
A major study of the diagnosis of ovarian cancer in the NHS found one in 10 GPs had requests for vital diagnostic tests refused in the past year.