Treatment: antidepressants (SSRIs, SNRIs, tricyclics, mianserin, agomelatine), especially in older people

No routine tests: depending on the patient

• Serum electrolytes (serum sodium, serum potassium) (age 60 or over, or risk of hyponatraemia)if neededBaseline serum sodium in people aged 60 or over ^[3] or at risk of hyponatraemia: diuretic, hypovolaemia, cirrhosis, other hyponatraemia-inducing drug ^[4,5,6]. Serum potassium to be corrected before citalopram, escitalopram or sertraline ^[4,5].
• Serum magnesium (heart disease or long QT, before citalopram, escitalopram or a tricyclic)if neededHypomagnesaemia increases the risk of arrhythmia and must be corrected before escitalopram ^[5]; it increases the proarrhythmic risk of tricyclics ^[7].
• ASTif neededMandatory before agomelatine, which is contraindicated if ALT or AST > 3 N ^[8]. Pre-existing liver disease: at baseline then every 6 to 12 months, whatever the antidepressant ^[3].
• ALT (agomelatine, or known liver disease)if neededMandatory before agomelatine, which is contraindicated if ALT or AST > 3 N ^[8]. Pre-existing liver disease: at baseline then every 6 to 12 months, whatever the antidepressant ^[3].
• Serum creatinine with eGFR (if older person or kidney disease, before duloxetine or mirtazapine)if needednon-French guidelineThe German NVL guideline measures GFR before any antidepressant ^[9]. In France, the SmPCs do not provide for this test, but duloxetine is not used in severe renal impairment and mirtazapine clearance may fall in moderate to severe renal impairment ^[10,11].
• Not a laboratory test: ECG before a tricyclic; to be considered before citalopram or escitalopram in case of heart disease (see the note).

1 week after starting an SSRI and after every dose change; otherwise 2 to 4 weeks after starting, or after adding a diuretic

• Serum electrolytes (sodium)
• Without waiting if headache, difficulty concentrating or memory problems, confusion, weakness, unsteadiness or a fall.

Before starting

• AST
• ALT

At around 3, 6, 12 and 24 weeks (and again in the same way after any dose increase)

• AST
• ALT

Depending on the situation

• FBC (on mianserin, if fever, sore throat or other sign of infection)if neededExceptional agranulocytosis, especially after 65: blood count if fever, sore throat or infection ^[22].
• Serum electrolytesif neededHypokalaemia, hyperkalaemia and hypomagnesaemia increase the proarrhythmic risk of tricyclics ^[7].
• Serum magnesium (tricyclic and heart disease, or QT-prolonging drug)if neededHypokalaemia, hyperkalaemia and hypomagnesaemia increase the proarrhythmic risk of tricyclics ^[7].
• Antidepressant level (mainly tricyclics)if needednon-French guidelineSevere or unusual adverse effects at low dose, or inadequate response at therapeutic dose; possibly useful for tricyclics ^[3].

Depending on the situation

• FBC (on mirtazapine, if fever, sore throat, stomatitis or other sign of infection)if neededBone marrow aplasia and agranulocytosis are very rare with mirtazapine, sometimes fatal, especially after 65: with these symptoms, stop the treatment and do an FBC ^[10].
• ASTif neededLiver injury mostly cytolytic, sometimes > 10 N, most often in the first months; caution with other hepatotoxic drugs; duloxetine is contraindicated in hepatic impairment ^[11].
• ALT (duloxetine: signs of liver damage, or another hepatotoxic drug)if neededLiver injury mostly cytolytic, sometimes > 10 N, most often in the first months; caution with other hepatotoxic drugs; duloxetine is contraindicated in hepatic impairment ^[11].
• INR (patient on a vitamin K antagonist, during the combination and when the antidepressant is stopped)if neededMore frequent INR monitoring recommended with sertraline, citalopram and fluoxetine ^[4,12,13]; INR increases reported with mirtazapine and duloxetine in patients on warfarin ^[10,11].
• Plasma glucose (diabetic patient, at the start of treatment and when stopped)if neededSSRIs, venlafaxine, mirtazapine and mianserin can destabilise glycaemic control in diabetic patients; on fluoxetine, hypoglycaemia during treatment and hyperglycaemia on stopping ^{[5,6,10,13,22]}.
• Lipid profile (long-term venlafaxine)if neededClinically significant rise in cholesterol in 5.3% of patients on venlafaxine for at least 3 months: consider measuring cholesterol long term ^[6].