Investigations
1st investigations to order
serum tryptophan
Test
Associated with the consumption of a diet low in tryptophan.
Result
low
urinary N-methylnicotinamide
Test
Urinary metabolites of niacin are very low.[80] Adults normally excrete 20% to 30% of niacin intake as N-methylnicotinamide and 40% to 60% as N-methyl-2-pyridone-5-carboxamide in the urine.
Result
low
urinary N-methyl-2-pyridone-5-carboxamide
Test
Urinary metabolites of niacin are very low.[80] Adults normally excrete 20% to 30% of niacin intake as N-methylnicotinamide and 40% to 60% as N-methyl-2-pyridone-5-carboxamide in the urine.
Result
low
urinary 2-pyridone/N-methylnicotinamide ratio
Test
The urinary 2-pyridone/N-methylnicotinamide is an indicator of niacin status. A ratio of <1 (mg/g creatinine) is indicative of niacin deficiency.[80]
Result
<1 (mg/g creatinine)
skin biopsy
Test
Confirmatory diagnostic test.
Result
non-specific dermatitic changes, perivascular lymphohistological infiltrates in the upper dermis, mild oedema in the papillary dermis, capillary dilatation, and dermal fibrosis; epidermal changes include early subcorneal blisters, pallor of the upper epidermis, hyperkeratosis, parakeratosis, as well as epidermal atrophy, detachment, and necrosis
photosensitivity testing
Test
Confirmatory diagnostic test involving the exposure of healthy skin to minimal erythema doses of ultraviolet light.
Other reactions include pruritic, burning, or tingling sensations.
Result
erythema, swelling, and blistering of skin
FBC
Test
Malnutrition and chronic alcohol use disorder are strongly associated with the development of vitamin B3 deficiency.
Result
microcytic anaemia in iron deficiency, macrocytic anaemia in vitamin B12 deficiency, elevated MCV in chronic alcohol use disorder
serum albumin
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in malnutrition
serum protein
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in malnutrition
LFTs
Test
Chronic alcohol use disorder is strongly associated with the development of vitamin B3 deficiency.
Result
elevated aspartate aminotransferase and alanine aminotransferase in hepatitis
gamma-GT
Test
Liver microsomal enzyme representing enzyme activation that may be induced by alcohol.
Chronic alcohol abuse is strongly associated with the development of vitamin B3 deficiency.
Result
elevated in chronic alcohol use disorder
Investigations to consider
serum total iron
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in iron deficiency
iron-binding capacity
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
increased in iron deficiency
ferritin
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in iron deficiency
transketolase activity
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low transketolase activity in vitamin B1 deficiency
thiamine pyrophosphate (TPP)
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
elevated TPP effect in vitamin B1 deficiency
riboflavin coefficient
Test
Riboflavin is the coenzyme for kynurenine hydroxylase, an enzyme involved in the conversion of tryptophan to niacin.[3][8] Its deficiency leads to impairment in the biosynthesis of niacin from tryptophan and may result in pellagra despite an adequate intake of niacin.[45]
Result
elevated in vitamin B2 deficiency
serum pyridoxal-5-phosphate
Test
Pyridoxal-5-phosphate is the coenzyme for kynureninase, an enzyme involved in the conversion of tryptophan to niacin.[3][8][44] Its deficiency leads to impairment in the biosynthesis of niacin from tryptophan and may result in pellagra despite an adequate intake of niacin.[45]
Result
low in vitamin B6 deficiency
serum cyanocobalamin
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in vitamin B12 deficiency
serum folic acid
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in folic acid deficiency
red cell folic acid
Test
Malnutrition is strongly associated with the development of vitamin B3 deficiency.
Result
low in folic acid deficiency
stool examination
Test
Malabsorption due to Crohn's disease, other gastrointestinal (GI) disease, and GI surgery is strongly associated with the development of vitamin B3 deficiency.
Result
may reveal malabsorption
neutral aminoaciduria
Test
Hartnup's disease is strongly associated with the development of vitamin B3 deficiency.
Result
>5 times upper limit of normal range in Hartnup's disease
serum serotonin
Test
False-positive elevations may be due to the consumption of serotonin-rich foods (e.g., bananas, avocados, nuts) or use of certain medications (L-dopa, paracetamol, salicylates).
Result
elevated in carcinoid syndrome
platelet serotonin
Test
False-positive elevations may be due to the consumption of serotonin-rich foods (e.g., bananas, avocados, nuts) or use of certain medications (L-dopa, paracetamol, salicylates).
Result
elevated in carcinoid syndrome
urinary 5-hydroxyindoleacetic acid
Test
False-positive elevations may be due to the consumption of serotonin-rich foods (e.g., bananas, avocados, nuts) or use of certain medications (L-dopa, paracetamol, salicylates).
Result
elevated in carcinoid syndrome
HIV antibodies
Test
HIV infection is associated with the development of vitamin B3 deficiency.
Result
positive in HIV infection
mental-state examination
ECG
Test
Typical changes suggestive of vitamin B3 deficiency may be seen. Niacin therapy normalises the ST-T changes.
Result
diffuse ST-T changes, ST depression and diphasic or flattened T waves, and inversions in leads II, III, aVF, and V1-V5
Use of this content is subject to our disclaimer