Table 1.

Blood monitoring requirements for commonly used DMARDs (adapted from NICE Clinical Knowledge Summaries)

Drug	Monitoring	Notable results (omit DMARD and discuss with specialist)a
		Full blood count	Urea & electrolytes	Liver function tests
		Methotrexate	2-weekly until 6 weeks after the last dose increase, monthly thereafter	White blood cells <3.5 × 109/L Neutrophils <2 × 109/L Platelets <150 × 109/L MCV >105 fLa	Moderate renal impairment (<50 mL/minute)	AST or ALT > twice the upper limit of normal
Sulfasalazine	Fortnightly for the first 3 months, then every 4 weeks for the second 3 months and 3-monthly thereafter	White blood cells <3.5 × 109/L Neutrophils <2 × 109/L Platelets <150 × 109/L MCV >105 fLa	Only required monthly for the first 3 months, clinically indicated thereafter Any sudden/large reduction in eGFR	AST or ALT > twice the upper limit of normal
Azathioprine	Weekly for 6 weeks and continue every 2 weeks until dose is stable for 6 weeks then monthly In patients heterozygous for TMPT, monitoring should be monthly (all tests)	White blood cells <3.5 × 109/L Neutrophils <2 × 109/L Platelets <150 × 109/L MCV >105 fLa	Only required 6-monthly Moderate renal impairment (<50 mL/minute)	AST or ALT > twice the upper limit of normal

^aIf mean cell volume (MCV) >105 fL check folate, vitamin B12, and thyroid-stimulating hormone. If abnormal treat any underlying abnormality. If normal discuss with specialist team. ALT= alanine aminotransferase. AST = aspartate aminotransferase. DMARD = disease-modifying antirheumatic drugs. eGFR = estimated glomerular filtration rate. TPMT = thiopurine methyltransferase.