Investigations
1st investigations to order
FBC
Test
Anaemia can point towards iron, copper, folate (B9), or B12 deficiency; these deficiencies are common in SBS. Thrombocytopenia may suggest haemolysis from vitamin E deficiency or liver disease as a consequence of intestinal failure.
Increased haemoglobin values indicate haemoconcentration and volume depletion.
Result
normal or anaemia, thrombocytopenia, or haemoconcentration
serum electrolytes
Test
Indirect signs of volume depletion or electrolyte disturbance.
Hypo- and hypernatraemia can reflect hydration status.
Hypokalaemia is very common in SBS and reflects nutritional deficiencies as well as possible magnesium deficiency. Magnesium deficiency may exist in spite of a normal serum magnesium concentration and, if clinically indicated, measurement of 24-hour urine magnesium may be required for diagnosis.
Hypomagnesaemia is common due to diarrhoea.
Bicarbonate can be elevated in a dehydrated patient, or may be low in a patient who has significant losses from a duodenal fistula or diarrhoea, or who has developed D-lactic acidosis owing to excessive oral carbohydrate intake.
Result
variably abnormal
serum urea and creatinine
Test
Indirect signs of volume depletion or electrolyte disturbance.
Reflect renal insufficiency from volume depletion.
Result
variably abnormal
serum albumin
Test
Low serum albumin concentration is common in the absence of parenteral nutrition and can be solely related to malabsorption.
Decreased albumin synthesis may be present due to intestinal failure-associated liver failure.
Result
low
serum calcium, zinc, selenium, folate
Test
Serum concentrations should be checked and rechecked approximately every 6 months once stable.
Result
low
vitamins A, B1, B2, B6, B12, C, D, and E
Test
Serum concentrations should be checked and rechecked approximately every 6 months once stable.
Serum vitamin B12 may be normal in the face of vitamin B12 deficiency.
Deficiencies in the fat-soluble vitamins A and D are commonly seen in SBS.
Vitamin E concentration should be measured in relation to total serum lipid concentration.
Water-soluble vitamin deficiencies are very rare in SBS (except for B12) due to efficient proximal absorption.
Result
low
methylmalonic acid (MMA)
Test
Used to confirm vitamin B12 deficiency.
Result
increased in vitamin B12 deficiency
INR
Test
The INR is used to detect vitamin K deficiency.
Vitamin K deficiency is rare in patients who have an intact colon (where vitamin K is synthesised by bacteria) and who have not received oral broad-spectrum antibiotics.
Result
increased in vitamin K deficiency
Investigations to consider
serum hepatic aminotransferases, alkaline phosphatase, and bilirubin (total and direct)
Test
In patients being supported with parenteral nutrition, elevations in alkaline phosphatase can be an early marker of liver damage and cholestasis.
Result
usually normal; abnormal in intestinal failure-associated liver disease
urine analysis
Test
Used to exclude nephrotic syndrome as a source of albumin loss.
Also indicated to test for haematuria and casts in patients with suspected kidney stones. A 24-hour urine test for oxalate may be useful.
Result
normal; proteinuria in nephrotic syndrome or haematuria in nephrolithiasis
serum D-lactate
Test
Used to exclude D-lactate acidosis in the presence of neurological signs, such as confusion or altered gait.
In patients with SBS, carbohydrates may be metabolised by colonic bacteria to D-lactate; therefore, excessive oral carbohydrate intake can lead to D-lactate acidosis. This can be a particular problem, as patients are encouraged to increase their oral intake to overcome malabsorption.
As lactic acid measurement provided by most laboratories only measure L-lactate, testing for D-lactate has to be specifically requested.
Result
D-lactate acidosis confirmed if >3 mmol/L
faecal fat quantification
Test
Used to confirm/estimate fat malabsorption.
Result
elevated in fat malabsorption
upper gastrointestinal contrast series
Test
This is not diagnostic and results must be interpreted in the context of clinical findings, since radiological length does not always correlate with function.
Other pertinent findings are dilated loops of bowel (amenable to surgical alteration) and anastomotic strictures.
Result
shortened intestinal length
Dual-energy x-ray absorptiometry (DXA) scan
Test
DXA scanning is used annually to monitor bone density, as patients are at high risk for osteopenia and osteoporosis due to vitamin D and calcium deficiencies.
Z-scores for lumbar spine and femoral neck, in a study of patients requiring parenteral nutrition, were -3.35 ± 3.49 and -2.23 ± 2.11, respectively.[25] In some patients with SBS, corticosteroids to treat Crohn's disease may further increase the risk of osteoporosis.
Result
osteopenia or osteoporosis
abdominal ultrasound
Test
Gallstones are common. In a study of 84 patients with SBS on parenteral nutrition, 44% were noted to have asymptomatic gallstones.[26]
Abdominal ultrasound should always be performed to exclude cholecystitis if any post-prandial right upper quadrant or epigastric pain is present.
Result
gallstones
CT abdomen
Test
A confirmatory test to diagnose renal stones if there are symptoms of dysuria, renal colic, or haematuria. Calcium oxalate kidney stones are common in patients with residual colon in continuity with small bowel.
Result
kidney stones
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