[Comparative performance of symptoms questionnaire, hydrogen test and genetic test for lactose intolerance].
BACKGROUND
Genetically programmed adult-type hypolactasia affects 56% of Chilean population. Ideally, diagnosis should be confirmed.


OBJECTIVE
To compare diagnostic yield of genetic test, hydrogen (H2) expiratory test and a validated symptomatic structured survey (SS).


METHODS
Patients submitted to H2 test answered a historic (anamnestic) and current SS (after the ingestion of 25 g of lactose). A blood sample was obtained for determination of genetic polymorphisms C/T_13910, C/G_13907 and G/A_22018 by polymerase chain reaction. The gold standard for diagnosis of lactose intolerance (LI) was the agreement of at least two of three tests.


RESULTS
Sixty-one participants aged 39 ± 12 years (21 males), were studied. Anamnestic SS was diagnostic of LI in all cases (score > 7), while current SS detected LI in 27/61 (46%). H2 test (an increase > 15 ppm after ingestion of 25 g of lactose) showed LI in 31/61 (51%). The locus C/G_13907 showed no polymorphism and locus G/A_22018 was in complete linkage disequilibrium with C/T_13910. Genotype C/C_13910, associated to hypolactasia, was present in 30/58 (52%). According to the gold-standard, 32/61 (52.5%) patients were diagnosed as LI. Sensitivity and specificity were, respectively, 79% and 69% for current SS, 93% and 93% for H2 test and 97% and 93% for the genetic test. The last two showed a positive likelihood ratio (LR) > 10 and a negative LR < 0.1, figures within the range considered clinically useful.


CONCLUSIONS
Genotype C/C_13910 is responsible for hypolactasia in this population. Anamnestic report of symptoms after milk ingestion and symptoms after lactose ingestion, are not accurate enough. H2 and genetic tests are simple and similarly accurate to diagnose lactose intolerance in adults.
Unidad de Gastroenterología, Departamento de Medicina, Facultad de Medicina, Universidad del Desarrollo-Clínica Alemana, Santiago, Chile. arollan@alemana.cl
Antonio
A
Rollán
Cecilia
C
Vial
Soledad
S
Quesada
Karena
K
Espinoza
Mary
M
Hatton
Alonso
A
Puga
Gabriela
G
Repetto
D000328:Adult; D000368:Aged; D005260:Female; D005838:Genotype; D006801:Humans; D043322:Lactase / Q000235:genetics; D007787:Lactose Intolerance / Q000175:diagnosis* / Q000235:genetics; D007789:Lactose Tolerance Test; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires; D055815:Young Adult
D043322:Lactase