Table 2

Addtional blood tests: responding to results

Elevated ESR/CRP	▸ Consider the following possibilities: –Infection. –Inflammation (including IBD). –Recurrent malignancy. –Non-GI causes (eg, rheumatoid arthritis, vasculitis, connective tissue disorders).
RBC folate deficiency	▸ Consider referral to dietitian for dietetic advice/supplementation. ▸ Check coeliac screen.
Iron deficiency: ferritin, % transferrin saturation, red cell indices	▸ If iron is low and iron saturation is low, discuss with supervising clinician and oncology team within 2 weeks. ▸ If intolerant of oral iron: consider intravenous iron infusion.
If excess iron=raised ferritin with transferrin saturation>45%	▸ Consider haemochromatosis: Discuss with supervising clinician and consider genetic testing.
Low vitamin B₁₂	▸ Exclude the possibility of inadequate dietary intake (especially vegans)—if this is the probable cause, consider trial of oral vitamin B₁₂ supplements. Dietetic referral. ▸ Consider possibility of pernicious anaemia—check parietal cell and intrinsic factor antibodies. ▸ Exclude SIBO (p. 27). Recheck result after treatment with antibiotics. ▸ Check coeliac screen. ▸ If confirmed on repeat testing and not treatable with oral replacement, eg, after gastrectomy, ask GP to arrange lifelong intramuscular replacement. ▸ Metformin therapy.
Abnormal thyroid function tests	▸ If TSH suppressed (<0.5 mIU/L), recheck result with thyroid auto antibodies. ▸ If TSH suppression confirmed, request GP to organise/refer for radiological imaging and treatment.
Abnormal thyroid function tests	▸ If TSH elevated (>4.0 mIU/L), recheck result. Also check 09:00 cortisol if Na ≤135 mmol/ L and K⁺ >4 mmol/L or raised urea or creatinine. ▸ If TSH elevation confirmed: start thyroid replacement medication. Request GP to monitor long-term. Review bowel function after 6–8 weeks.
Abnormal coeliac serology	▸ If IgA deficient, request IgG coeliac screen. ▸ If TTG elevated, confirm with SI biopsy. ▸ Refer for dietetic advice once diagnosis is confirmed. ▸ Refer to coeliac clinic.
Serum Mg²⁺	▸ If <0.3 mmol/L, this is an emergency. ▸ Check K⁺ and Ca²⁺, if low, will also need replacement. ▸ If 0.3–0.5, consider intravenous replacement if symptomatic or fall in Mg₂ level has been acute. If oral replacement is given, check for response after 5–7 days with repeat blood tests. ▸ If oral replacement is used, Mg Oxide or Mg aspartate provide better bioavailability and cause less diarrhoea than other Mg preparations. ▸ If associated with refeeding syndrome, also monitor PO₄ and K⁺ closely and give intravenous vitamin replacement.

Ca, calcium; CRP, C reactive protein; ESR, erythrocyte sedimentation rate; GI, gastrointestinal; GP, general practitioner; IBD, inflammatory bowel disease; K, potassium; Mg, magnesium; Na, sodium; PO₄, phosphate; RBC, red blood cell; SIBO, small intestinal bacterial overgrowth; TSH, thyroid stimulating hormone; TTG, tissue transglutaminase.