Constipation (adult and child)

Laboratory tests

• FBC (if organic disease suspected or alarm signs)if neededThe French SNFCP recommendation (2017) rules out routine blood tests as first-line, for lack of yield, and reserves them for failure of initial treatment, suspected organic disease or alarm features; these tests comprise FBC, serum creatinine, serum calcium, plasma glucose, thyroid hormones and CRP ^[3]. The AGA technical review asks for an FBC ^[1]; the American Family Physician review rules out routine blood tests without alarm features ^[4]; the Japanese guideline decides case by case ^[5].
• TSH (signs of hypothyroidism, or recent onset without cause)if neededHypothyroidism is a metabolic cause of constipation; routine testing has an unassessed, probably very low yield: reserve it for clinical suspicion ^[1]. First-line, TSH alone ^[6]. The SNFCP (2017) places it in the tests reserved for treatment failure or suspected organic disease ^[3].
• Fasting plasma glucose (risk factors or signs of diabetes)if neededIncluded in the SNFCP (2017) tests, reserved for failure of initial treatment, suspected organic disease or alarm features ^[3]; diabetes is a metabolic cause (neuropathy) ^[1].
• Serum calciumif neededCalcium and creatinine are part of the SNFCP (2017) tests, reserved for failure of initial treatment, suspected organic disease or alarm features ^[3]; electrolytes come from the AGA review: hypercalcaemia, hypokalaemia and uraemia are metabolic causes, and diuretics may cause constipation through electrolyte disturbances ^[1].
• Serum electrolytesif neededCalcium and creatinine are part of the SNFCP (2017) tests, reserved for failure of initial treatment, suspected organic disease or alarm features ^[3]; electrolytes come from the AGA review: hypercalcaemia, hypokalaemia and uraemia are metabolic causes, and diuretics may cause constipation through electrolyte disturbances ^[1].
• Serum creatinine with GFR (clinical suggestion, diuretic, renal impairment)if neededCalcium and creatinine are part of the SNFCP (2017) tests, reserved for failure of initial treatment, suspected organic disease or alarm features ^[3]; electrolytes come from the AGA review: hypercalcaemia, hypokalaemia and uraemia are metabolic causes, and diuretics may cause constipation through electrolyte disturbances ^[1].
• CRP (failure of initial treatment, suspected organic cause or alarm signs)if neededIncluded in the SNFCP (2017) blood tests, which it does not recommend routinely as first-line ^[3].
• Serum magnesium (if the context suggests hypomagnesaemia)if needednon-French guidelineHypomagnesaemia is one of the metabolic causes of constipation ^[1]; measure only if the context suggests it.

• Functional constipation without red flags: no laboratory tests.

Laboratory tests (growth faltering, or refractory constipation at the specialist's request)

• IgA anti-tissue transglutaminase antibodies (tTG-IgA)if neededGrowth faltering: look for coeliac disease; refractory constipation: at the specialist's request ^[7]. Test indicated first-line in a child suspected of coeliac disease ^[6].
• Total IgAif neededGrowth faltering: look for coeliac disease; refractory constipation: at the specialist's request ^[7]. Test indicated first-line in a child suspected of coeliac disease ^[6].
• TSHif needednon-French guidelineGrowth faltering: look for hypothyroidism; refractory constipation: at the specialist's request ^[7].
• Serum calcium (if constipation persists despite well-conducted treatment)if needednon-French guidelineConstipation that persists despite well-conducted behavioural management and laxative treatment: the Australian guideline of the Royal Children's Hospital Melbourne proposes looking for rarer organic causes, including hypercalcaemia, together with coeliac disease and hypothyroidism ^[8]; the American Family Physician review measures calcium if hypercalcaemia is suspected ^[9]. NICE retains, at the specialist's request, only coeliac disease and hypothyroidism ^[7].