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Asthma Predictive Index (API)

Calculators  Respiratory
The Asthma Predictive Index (API) is a classification tool that helps predict the likelihood of pediatric patients ≤ 3 years of age developing asthma.
noisily breathing episodes/year
>=3 50
<3 100
A father or mother with asthma
No 0
Yes 10
Patient has eczema
No 0
Yes 10
Patient with allergic rhinitis
No 0
Yes 1
noisily breathing episodes apart from colds
No 0
Yes 1
Eosinophilia count (≥4% on CBC)
No 0
Yes 1


Measured Factor
Likelihood of developing childhood asthma.
Measured Factor Disease
  • Childhood asthma
Measured Factor Detail
The Asthma Predictive Index or API provides a good method for predicting the likelihood of developing childhood asthma in children ≤ 3 years of age. The index or score is based on frequent wheezing during the first 3 years of life, one major risk factor (parental history of asthma or eczema) or two of three minor risk factors (eosinophilia, wheezing without colds, and allergic rhinitis). With this information, two indices are developed for the prediction of asthma. Positive and negative likelihood of developing asthma is further divided into loose or strict. A strict negative indicates a strong likelihood that the child will not develop asthma, while a loose negative indicates it is less likely the child will develop asthma. A strict positive indicates a very high chance the child will develop asthma, while a loose positive indicates it is likely the child will develop asthma.
Body System
Measured Factor High Impact
  • A very high chance the child will develop asthma

Result Interpretation

Ranges Ranges
  • Critical High: Positive by strict criteria | 95% specific for later childhood asthma diagnosis
  • Normal: Negative
  • Normal Pediatric: Negative
Result High Conditions
  • Childhood asthma
Test Limitations
The Asthma Predictive Index or API adds considerable costs to the diagnosis because of the blood test that needs to be perfomed. More simpler rules can effectively replace the API. Additionally, the predictive performance of the API is modest and similar to prediction based only on preschool wheeze.  The low performance of the API might be because the original study only included children who had complete information for all predictor values and had sufficient information to confirm a positive or stringent API.
References: 2


Study Validation 1
Randomized study comparing the predictive performance of the Asthma Predictive Index (API) with other simpler rules based only on wheezing. Additionally, the study also aimed to predict the accuracy of prediction of the API in a population that differs from the population (Tucson) used in the development of the index. The study included 1954 children who were followed from age 1 to 10 years.  Throughout the study period, children were assessed at 3 years of age for frequency of wheezing and then again at ages 7 and 10 years to determine their association with asthma.To assess the results, test characteristics and measures of descriptive performance were evaluated. Results showed that the ability of the API to predict asthma in this study population was comparable to the population used in Tucson. For the loose API, odds ratio for asthma at age 7 years were 5.2 in Leicester (5.5 in Tucson), and positive predictive values were 26% (26%). For the stringent API, the values were 8.2 (40%) and 9.8 (48%), respectively. The discriminative ability of all prediction rules was moderate (c statistics </= 7) and overall predictive performance low (Scaled Brier score < 20%). In conclusion, the study demonstrated a comparable, but modest predictive performance of the API when compared to the results in the Tucson population. Additionally, the predictive performance of the API was also similar to the predictive capabilities of prediction based only on preschool wheeze. In conclusion, better prediction rules are still needed.
References: 2
Study Validation 2
Exploratory study aimed at evaluating the validity of the Asthma Predictive Index (API) for a retrospective study, because the API has only been used in prospective and cross-sectional studies thus far. Study utilized data from residents of Olmsted County in Rochester, Minnesota and consisted of a sample of children who participated in a previous retrospective cohort study. The API was operationalized by 2 or more wheezing episodes in a year during the first 3 years of life plus one of the major criteria or two of the minor criteria described in the original API. To assess criterion validity, kappa and agreement rates between the API and the Predetermined Asthma Criteria (PAC) were measured. Additionally, the association of API with known risk factors for asthma was also determined. A total of 105 children were included in the study, 15 children (14.3%) met the API criteria and 33 (31.4%) met the PAC criteria. Agreement rate and kappa between API and definite asthma of PAC were 89.5% and 0.66 (p<0.01). These results demonstrated that application of the API to a retrospective study for ascertaining asthma is appropriate.
References: 3
Study Additional 1
Review article discussing the importance of determining at an early age which children will develop asthma later in life, analyzing the pros and cons of different predictive indices, and the efficacy of the Asthma Predictive Index (API). Asthma is the most prevalent chronic disease in children, but diagnosis and management is primarily based on subjective clinical findings. Chronic inflammation is the most common feature of asthma, but measurements of airway inflammation for diagnosis of asthma are too invasive for routine use. Various scoring systems exist that take into account different factors such as family history, frequency of chest infections and obstructive airway disease scores among others. Of all the scoring systems available, the API remains the simplest and less expensive one. The API has a negative predictive value of 93.9% at 6 years of age for children who are early wheezers during the first 3 years of life. Likewise, for children who are frequent wheezers during the first 3 years of life the negative predictive value was 91.6% at 6 years of age. Thus, the API remains the best and simplest tool to use in every health care setting.
References: 4
Study Additional 2
Review article providing support to demonstrate the clinical importance of the Asthma Predictive Index or API. No biochemical or other medical test is available to determine which children will develop asthma, thus the API was created as a tool to predict the development of asthma in children in a noninvasive way. The API has been validated as a clinical tool in various studies and studies have replicated the findings of the original study by Castro-Rodriguez et al. The sensitivity, specificity, positive and negative predictive values of the API was assessed at 6,8,11 and 13 years of age by Castro-Rodriguez et al. The API demonstrated a modest sensitivity (14.8% to 27.5%), but had a very high specificity (greater than 96%). Independent studies in Colombia and the Netherlands also demonstrated the high specificity of the API, 79.2% and 92%, respectively. Major strengths of the API are found in its design, it is a simple set of equally weighted criteria with a binary scoring system. Other predictive indexes have been developed, but non has performed as well and thus the API remains the most useful.
References: 5
Study Additional 3
Observational, cross sectional study evaluated the association between the Asthma Predictive Index (API) and fractional exhaled nitric oxide (FE NO) levels in children younger than 3 years with recurrent wheezing. In the past, measurement of FE NO have been used as markers of eosinophilic airways inflammation in asthma patients because of the characteristic inflammation that accompanies the disease. The FE NO was measures by a chemiluminescence analyzer during tidal breathing. Only children who were inhaled corticosteroid-naive or leukotriene receptor antagonist-naive were included. Study population consisted of 52 children between the ages of 5 and 36 months old. Patients with a positive API made up 60% of the population and had higher FE NO levels than those with a negative API (p<0.01). A high FE NO was seen in 74% of children with positive API and in 26% of those with a negative API (p<0.01). In conclusion, the study found an association between a positive API and high levels of FE NO in children who were younger than 3 years of age with recurrent wheezing.
References: 6


Jose Castro Rodriguez, MD. PhD is an assistance professor of family medicine and pediatrics at Pontifica Universidad Catolica in Chile. His research interests focuses on respiratory diseases in pediatric patients,


  1. Castro-Rodríguez JA, Holberg CJ, Wright AL, Martinez FD. A clinical index to define risk of asthma in young children with recurrent wheezing. Am J Respir Crit Care Med. 2000 Oct;162(4 Pt 1):1403-6.
  2. Leonardi NA, Spycher BD, Strippoli MP, Frey U, Silverman M, Kuehni CE. Validation of the Asthma Predictive Index and comparison with simpler clinical prediction rules. J Allergy Clin Immunol. 2011 Jun;127(6):1466-72.e6.
  3. Wi CI, Park MA, Juhn YJ. Development and initial testing of Asthma Predictive Index for a retrospective study: an exploratory study. J Asthma. 2015 Mar;52(2):183-90.
  4. Castro-Rodriguez JA. The Asthma Predictive Index: a very useful tool for predicting asthma in young children. J Allergy Clin Immunol. 2010 Aug;126(2):212-6.
  5. Huffaker MF, Phipatanakul W. Utility of the Asthma Predictive Index in predicting childhood asthma and identifying disease-modifying interventions. Ann Allergy Asthma Immunol. 2014 Mar;112(3):188-90.
  6. Balinotti JE, Colom A, Kofman C, Teper A. Association between the Asthma Predictive Index and levels of exhaled nitric oxide in infants and toddlers with recurrent wheezing. Arch Argent Pediatr. 2013 Jun;111(3):191-5.

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