As a physician, what blood value indicators determine if methotrexate needs to be discontinued?

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"Warnings:
methotrexate should be used only by physicians whose knowledge and experience
include the use of antimetabolite therapy.
Because of the possibility of serious toxic reactions (which can be fatal):
methotrexate should be used only in life threatening neoplastic diseases, or in patients with psoriasis or rheumatoid arthritis with severe, recalcltrant, disabling disease which is not adequately responsive to other forms of therapy. Deaths have been reported with the use of methotrexate in the treatment of malignancy, psoriasis, and rheumatoid arthritis.
Patients should be closely monitored for bone marrow, liver, lung and kidney toxicities. (See precautions.)"

"Laboratory Tests:

Patients undergoing methotrexate therapy should be closely monitored so that toxic effects are detected promptly. Baseline assessment should include a complete blood count with differential and platelet counts, hepatic enzymes, renal function tests, and a chest X-ray. During therapy of rheumatoid arthritis and psoriasis, monitoring of these parameters is recommended: hematology at least monthly, renal function and liver function every 1 to 2 months. More frequent monitoring is usually indicated during antineoplastic therapy. During initial or changing doses, or during periods of increased risk of elevated methotrexate blood levels (e.g., dehydration), more frequent monitoring may also be indicated. Transient liver function test abnormalities are observed frequently after methotrexate administration and are usually not cause for modification of methotrexate therapy. Persistent liver function test abnormalities, and/or depression of serum albumin may be indicators of serious liver toxicity and require evaluation. (See PRECAUTIONS, Organ System Toxicity, Hepatic.)"
Source and further information:
http://www.rxlist.com/trexall-drug.htm