Screening
Ada M. Fenick
PRINCIPLES OF SCREENING
Much of the history and physical examination obtained at each health supervision visit is directed toward the identification of undetected problems or their risk factors in an effort at secondary prevention of undesirable outcomes. Screening for these conditions implies the presumptive identification of disease in an asymptomatic individual before it becomes clinically evident. Screening is not diagnostic; a patient with a positive screening test must undergo further evaluation for definitive diagnosis.1 Pediatricians must be aware not only of current recommendations regarding screening and the specific tests available but also of the basic principles and concepts behind screening in order to evaluate whether a given program does more good than harm for their particular patients and community.
Screening assumes that identified persons will undergo definitive diagnostic testing and will subsequently benefit by earlier implementation of treatment or prevention programs. In deciding what conditions are worth screening for, the clinician must consider the following:
• Is the disease common in the population and serious enough to warrant screening?
• Is there an acceptable treatment for the patients who have the condition?
• Will early diagnosis favorably influence the outcome?
• Is there a good screening test available?2
The effectiveness of a given screening program can be demonstrated by performing a randomized clinical trial in which all pertinent outcomes are evaluated. Unfortunately, such data are often lacking or difficult to obtain. In the absence of such studies, the value of a given screening program must be defined in relation to the characteristics of the condition being screened for, the test being used, the population being evaluated, and the larger social context in which decisions regarding the value of detection and the allocation of resources are being made.
Identification of conditions for which no treatment exists or for which the benefit of existing therapy is unproven, is of questionable value, or is potentially harmful. Even if an effective intervention exists, the clinician must weigh the potential risks and benefits of the treatment itself with that of the identified condition and consider the impact of public acceptance on compliance with recommendations about screening and treatment.2
The costs associated with a screening program must be broadly defined. Costs include not only the screening itself but also the subsequently required diagnostic, therapeutic, and supportive services.2 The psychological impact on individuals identified as false positives and the costs involved in definitive evaluation of these individuals may be significant and should not be underestimated.3,4 (See also Chapter 98.)
Early identification through screening does not always imply a better outcome. If the health care system or community is unable to provide the necessary subsequent diagnostic and therapeutic services, the ultimate value of the screening program is questionable. In addition, if persons at greatest risk do not avail themselves of the screening program, or if individuals with abnormal screening tests do not follow through with subsequent diagnostic and therapeutic recommendations, the screening program will fail to achieve the benefits intended.
Besides not being harmful to the individual being tested, a good screening test must also be accurate. The accuracy of a test is described by its sensitivity and specificity when compared with gold-standard measures of the presence or absence of disease and by its positive and negative predictive value within a population with a given disease prevalence.2 It is important to understand how these test characteristics affect the overall value of screening programs and strategies for their implementation. 
If the population on which the test was standardized is sufficiently similar to the group to be screened, then measures of predictive ability will be comparable and the application of the instrument is appropriate. Clinically, the positive predictive value of a test may be of paramount importance to a patient and provider; the provider must know the prevalence of the condition in his practice in order to effectively interpret the result of the screen for his patient. Independent of the sensitivity and specificity of the screening test, diminishing population prevalence of the condition being sought diminishes the positive predictive value of the test by changing the proportion of true-positive to false-positive results. For most screening situations, it is important to know the predictive ability of the test in a population with low disease prevalence, because this is generally how screening tests are used. In many cases, selective testing of high-risk subgroups may make more sense than mass screening.2
Current recommendations regarding screening during routine health supervision visits reflect an increasing awareness of the importance of these issues in deciding the value of specific screening programs. Some screening programs are applicable universally because of a high prevalence in the population, while some screening should be done on the basis of selective factors; different strategies may be appropriate for different populations.5,6 The following section addresses specific recommendations for screening during the health supervision visit. Areas of health screening unique to adolescents are discussed in Chapter 67.
SPECIFIC SCREENING AREAS
THE PHYSICAL EXAMINATION
During routine health surveillance visits, a physical examination should be performed for diagnostic and case-finding (screening) purposes; it also provides a useful framework for parent and child education and reassurance.6 Height, weight, head circumference (ages 0 to 3 years), and body mass index (over age 2) should be monitored sequentially as part of the physical examination as detailed in Chapters 10 and 28.5
NEWBORNS
The American College of Medical Genetics recommends that all states screen in the early neonatal period for a core panel of 29 metabolic diseases and hemoglobinopathies, with another 25 disorders recommended for inclusion either because of the benefit of early diagnosis or because of their potential for confusion with the core panel disorders.7 All states in the United States have initiated neonatal screening programs, and all screen for congenital hypothyroidism, phenylketonuria (PKU), and galactosemia, but the absence of federal guidelines has led to considerable state-to-state variability in other measures.8 The Maternal and Child Health Bureau has recently begun to move toward standardization of outcomes and guidelines for state newborn screening programs.7
To minimize the number of infants inadvertently missed by the screening program, a blood sample should be obtained on all full-term neonates just before hospital discharge. In no case should this be obtained later than 7 days of age.9 Special testing arrangements must be made if birthing takes place in a nontraditional setting. Identification of some disorders, such as phenylketonuria, requires sufficient buildup of metabolites to be detected; thus, if blood was drawn before the infant was 24 hours old (eg, due to early discharge), a second sample should be obtained when the child is 1 to 2 weeks old. Blood transfusions and dialysis, by introducing foreign blood cells and reducing concentrations of circulating metabolites, may result in both false-negative and false-positive results when newborns are screened for metabolic disorders and hemoglobinopathies.3 When feasible, samples should be obtained before these procedures. However, preterm and sick infants should be screened by 1 week of age regardless of the presence or absence of these or other factors (parenteral feeding, antibiotic use, prematurity) that may interfere with specific assays or the interpretation of test results. Where such concerns exist, a repeat sample should be obtained at a time interval appropriate to resolution of the confounding factors. Because of variability in disease presentation and the technical aspects of screening, some affected infants may test falsely normal on their initial screen. Therefore, regardless of the results of the newborn screening, specific diagnostic testing should always be performed when clinical suspicions warrant.
Because of the rapid pace of change regarding newborn screening, and because the disorders screened for are rare, the Committee on Genetics of the American Academy of Pediatrics periodically issues updated information for physicians regarding currently available tests and screening recommendations.10 Because the choice of screening test, threshold values, and implementation strategies vary in different states and countries, providers should be familiar with the methodology, standards, and follow-up procedures for their regional screening program.3
DEVELOPMENT
See Chapter 82, “Standardized Screening and Assessment Instruments.”
Vision Screening
Routine vision screening is an effective way to identify otherwise unsuspected problems that are amenable to correction. Because normal visual development depends on the brain’s receipt of clear binocular visual stimulation, and because the plasticity of the developing visual system is time-limited, early detection and treatment of a variety of problems impairing vision are essential to preventing permanent and irreversible visual deficits. An age-appropriate assessment should be incorporated into each health supervision visit beginning with the newborn examination. At all ages, the examination should include a review of relevant historical information regarding visual concerns and family history, gross inspection of the eye and surrounding structures, observation of pupillary symmetry and reactivity, assessment of ocular movements, elicitation of the red reflex (to detect opacities and asymmetries in the visual axis), and age-appropriate methods to assess ocular preference and alignment and visual acuity. A successful funduscopic examination should be attempted beginning at 3 years of age and can generally be accomplished by 5 years of age.13
It is especially important to assess the red reflex during the neonatal period. Identification of an absent, defective, or asymmetric red reflex should lead immediately to either a repeat examination following pupillary dilation or referral to an experienced pediatric ophthalmologist for definitive diagnosis.
In the infant, ocular preference and alignment and visual acuity can be grossly assessed by observing the baby’s ability to visually track an object, noting any behavioral cues of an eye preference by alternately covering each eye while presenting an interesting object and observing the position and symmetry of the light reflected off the corneas when a light is held several feet in front of the eyes (corneal light reflex).13 Ocular alignment (conjugate gaze) should be consistently present by 4 months of age; a child with ocular deviation by history or examination after this time should be referred for evaluation by an ophthalmologist.15
The toddler and preschooler should have ocular preference and alignment assessed via the corneal light reflex, but at this age, the cross cover test should be utilized as well. This test involves covering and uncovering each eye while the child is looking straight ahead at an object approximately 10 feet away. The observation of any movement of the uncovered eye when the opposite is covered or of the covered eye when the occluder is removed suggests potential ocular misalignment (strabismus). By 3 to 5 years of age, stereoscopic vision can also be assessed using the random-dot-E stereotest or stereoscopic screening machines. A positive test via any of these modalities warrants referral to an ophthalmologist for further evaluation.13 Regardless of the underlying etiology, strabismus that is left untreated will eventually result in cortical suppression of visual input from the nondominant eye and the absence of depth perception, making early detection and treatment critical.
Formal visual acuity testing should begin at 3 years of age using age-appropriate methods.13 Approximately 5% to 10% of all preschoolers have refractive errors.16 While picture tests such as the Lea Hyvärinen (LH) test and Allen picture cards are most effective for screening preschoolers, by 5 years of age, most children can be successfully screened using a wall chart with the standard Snellen alphabet chart, the tumbling-E test, or the HOTV test. School-aged children, including adolescents, should have their acuity checked yearly. Preschoolers should be referred for further testing if the acuity in either eye is 20/40 or worse. In children over age 6, inability to read the majority of a 20/30 line warrants referral. At all ages, a difference of more than one line in the acuity measurements between eyes necessitates further evaluation.13
For more detailed discussions of the approach to office evaluations of the eyes and tests of vision, refer to Chapters 580 and 581.
Hearing Screening
Approximately 1 to 3 of every 1000 infants are born deaf, and many children develop hearing deficits during childhood.17 Timely detection of these problems allows for earlier initiation of interventions aimed at enhancing the communication, social, and educational skills of these children. When deaf or hard-of-hearing children are identified earlier than 6 months of age, they perform as much as 20 to 40 percentile points higher on school-related testing.18
Hearing of all infants should be screened by 1 month of age.18 In the United States, 31 states require newborn hearing screening, while 17 more offer it to all newborns.8 At this time, otoacoustic emissions (OAE) and automated auditory brainstem response (AABR) testing are available for testing in the newborn period. In both these modalities, a series of stimuli is presented to the infant via a probe in the ear canal. However, OAE measures cochlear responses to an acoustic stimulus via a probe in the canal, while AABR measures neural activity in response to a series of acoustic stimuli via surface electrodes. While both modalities can detect sensory hearing loss, only the AABR may detect hearing loss associated with neural dysfunction. AABR can be used to retest a child who has not passed the OAE, as it can verify an intact pathway. However, the opposite is not true; a child who has not passed the AABR because of neural dysfunction may have an intact sensory system, pass an OAE examination, and not receive appropriate referral for the root cause. Any child who does not pass a newborn hearing screen should receive a comprehensive evaluation by 3 months of age by an audiologist who has the necessary expertise and equipment.18
Because not all hearing loss will be uncovered by newborn screening, and because some hearing loss is later in onset, all children with risk factors listed in Table 12-1 should have their hearing evaluated at least once by 2 to 2½ years of age.18 In addition to performing a gross hearing assessment and inquiring about hearing concerns at each well-child visit, the American Academy of Pediatrics endorses a policy of formal hearing screening for all children at 4, 5, 6, 8, and 10 years old.5 A variety of transient conditions as well as testing problems can affect the hearing evaluation of older, otherwise healthy children, and so the results of audiologic screening must be interpreted within the context of the child’s ear-disease history and physical findings.
For further discussion of hearing evaluation see Chapter 369.
BLOOD PRESSURE SCREENING
Routine blood pressure screening during the well-child visit allows for the identification and potential treatment of children with persistently elevated blood pressure who are at increased risk for hypertension and its subsequent complications as adults. In a minority of patients, an underlying medical etiology may be found. Screening also provides an opportunity to evaluate and potentially modify additional cardiovascular risk factors and to provide education regarding prudent dietary and lifestyle choices.
Table 12-1. Risk Indicators Associated with Hearing Loss
