That could include review of antipsychotic plasma concentrations if available. The prescriber, patient, pharmacy  and the laboratory performing blood counts are all registered with a specified clozapine provider who must be advised that there is no history of neutropenia from any cause. The clozapine providers collaborate by sharing information regarding patients who have had clozapine related neutropenia or agranulocytosis so that clozapine cannot be used again on license. Clozapine may only be dispensed after a satisfactory blood result has been received by the risk monitoring agency at which point an individual prescription may be released to an individual patient only.Baseline tests usually also include; a physical examination including baseline weight, waist circumference and BMI, assessments of renal function and liver function, an ECG and other baseline bloods may also be taken to facilitate monitoring of possible myocarditis, these might include C reactive protein (CRP) and troponin. In Australia and New Zealand pre-clozapine echocardiograms are also commonly performed. A number of service protocols are available and there are variations in the extent of preclozapine work ups. Some might also include fasting lipids, HbA1c and prolactin. At the Maudsley Hospital in the UK the Treat service also routinely performs a wide variety of other investigations including multiple investigations for other causes of psychosis and comorbidities including; MRI brain imaging, thyroid function tests, B12, folate and serum calcium levels, infection screening for blood borne viruses including Hepatitis B and C, HIV and syphilis as well as screening for autoimmune psychosis by anti-NMDA, anti-VGKC and Anti-nuclear Antibody  screening.
However severe agranulocytosis can result in spontaneous infection and death, is a severe decrease in the amount of a specific kind of white blood cell called granulocytes. Clozapine carries a black box warning for drug-induced agranulocytosis. Rapid point-of-care tests may simplify the monitoring for agranulocytosis. Clozapine rechallenge
A clozapine "rechallenge" is when someone that experienced agranulocytosis while taking clozapine starts taking the medication again. In countries in which the neutrophil thresholds are higher than those used in the US a simple approach is, if the lowest ANC had been above the US cut off, to reintroduce clozapine but with the US monitoring regime. This has been demonstrated in a large cohort of patients in a hospital in London in which it was found that of 115 patients who had had clozapine stopped according to the US criteria only 7 would have had clozapine stopped if the US cut offs had been used. Of these 62 were rechallenged, 59 continued to use clozapine without difficulty and only 1 had a fall in neutrophils below the US cut off. Other approaches have included the use of other drugs to support neutrophil counts including lithium or granulocyte colony-stimulating factor (G-CSF). However, if agranulocytosis still occurs during a rechallenge, the alternative options are limited. Cardiac toxicity
Clozapine can rarely cause myocarditis and cardiomyopathy.