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Recommendations Summary

CF: Nutrition Assessment and Diagnosis of Nutrition Status 2020

Click here to see the explanation of recommendation ratings (Strong, Fair, Weak, Consensus, Insufficient Evidence) and labels (Imperative or Conditional). To see more detail on the evidence from which the following recommendations were drawn, use the hyperlinks in the Supporting Evidence Section below.

  • Recommendation(s)

    CF: Frequency of Nutrition Assessment

    In individuals with cystic fibrosis (CF), a full nutrition assessment should be conducted by an RDN or international equivalent:

    • at diagnosis;
    • when indicated by nutrition screening;
    • up to monthly for the first 6 months of life; up to every other month until 1 year of age; and up to quarterly until 2 years of age;
    • annually for individuals greater than 2 years of age and;
    • when disease or treatment course changes.

    Rating: Consensus

    CF: Nutrition Assessment Components

    In individuals with cystic fibrosis (CF), the RDN or international equivalent should diagnose nutrition status, including underweight and overweight, based on a comprehensive assessment of weight and growth history and stature, body composition, disease severity, laboratory values, drug-nutrient interactions/implications, and estimated energy expenditure compared to client/parent report of dietary intake and food security status, since CF nutrition pathology is highly individual and maintaining optimal nutrition status is a necessary component of preventing disease progression.

    Rating: Strong

    • Risks/Harms of Implementing This Recommendation

      There are no obvious risks or harms associated with these nutrition assessment recommendations. Time spent in cystic fibrosis clinics is the most common objection to nutrition assessment.

    • Conditions of Application

      Changes in Disease Course or Treatment: Significant changes in disease or treatment course that warrant full nutrition assessment include, but are not limited to: diagnosis of a co-morbidity (ex: CFRD, liver disease, CF-related bone disease); unintentional weight loss or gain; hospitalization for pulmonary exacerbation; pre-, peri- and post- lung transplantation; exacerbation in gastrointestinal symptoms; beginning or ceasing enteral or parenteral nutrition; beginning, change or cessation of medications including CFTR modulation therapy or PERT; and abnormal nutrition-related laboratory values.

      Socioeconomic Status (SES): There is potential that individuals and families with lower SES will have more difficulty paying for additional testing to diagnose nutrition status beyond BMI/weight measurements. In these cases, practitioners may utilize low-cost options such as nutrition-focused-physical exams.

      WHO vs CDC growth curves: In accordance with recommendations for the general population, practitioners may use WHO growth standards for infants 0-24 months of age and begin using CDC growth charts at age two (Grummer-Strawn et al 2010) though this is not currently specified in guidance for the CF population (Cystic Fibrosis Foundation, 2019) For infants and children 0-24 months of age, WHO growth charts, compared to CDC growth charts, were less likely to define children as <50th percentile for weight-for-age (WFA) and weight-for-length (WFL) (Machogu et al 2015, Zhang et al 2015) Therefore, if practitioners use WHO growth charts to screen for growth, percentiles <70th percentile may be used to identify nutrition risk rather than the <50th percentile recommended when using CDC growth charts.

    • Potential Costs Associated with Application

      There is potential that using certain methods to assess nutrition status will be cost prohibitive or difficult to institute in clinical practice (ex: DEXA for body composition or laboratory measures such as essential fatty acid levels), particularly for individuals with low socio-economic statis and/or without insurance coverage. Nutrition assessment and interventions can reduce inequities by assisting individuals and families in determining options for improving or maintaining nutrition and disease progression as well as accessing resources to minimize food insecurity. In clinical practice, families who attend CF clinic regularly and are connected with resources are more likely to benefit than those who seldom attend CF clinic and are unaware of available resources (Cystic Fibrosis Foundation, 2019).

    • Recommendation Narrative

      Background. Malnutrition can occur quickly and insidiously in individuals with cystic fibrosis (CF) due to multiple dynamic factors including malabsorption, decreased appetite, increased energy expenditure, CF related diabetes, and psychosocial factors. Health care providers, individuals with CF and their families should recognize that representation of adequate nutritional status extends beyond the sole use of BMI, and should reflect body composition, laboratory values, energy expenditure, and dietary intake. Consistent, individualized, and ongoing assessment of nutrition status may prevent or remediate the effects of malnutrition on the progression of pulmonary disease and improve quality of life for individuals with CF.

      Evidence. There was no evidence that examined overall nutrition assessment protocols in isolation, but in quality improvement studies, increased contacts between individuals with CF/family and an RDN, including nutrition screening and assessment, resulted in improved anthropometric outcomes and decreased antibiotic use in pediatric individuals with CF (Ledger et al 2013, Starket al 2011, Savant et al 2014, Ramirez et al 2015) There were no studies of this nature available that examined adults with CF.

      The systematic review supporting this guideline clearly demonstrated that undernutrition, defined by weight and length/height measures, is longitudinally associated with pulmonary decline and mortality in pediatric individuals and adults with CF. (Academy of Nutrition and Dietetics 2019, Darrah et al 2016, Emerson et al 2002, Goss et al 2018, Keller et al 2003, Konstan et al 2007, Lai et al 2009, Machogu et al 2015, McPhail et al 2008, Sanders et al 2014, Sanders et al 2015, Sanders et al 2015, Sanders et al 2018, Usatin et al 2017, Welsh et al 2014, Woestenenk et al 2014, Yen et al 2013, Amadori et al 2009, Ramos et al 2017, George et al 2011, Chamnan et al 2010, Stephensonet al 2015, Vieni et al 2013, McColley et al 2017). However, only evaluating weight and growth measures may overlook other complex factors that contribute to poor nutritional status and ultimately poorer lung function.  For example, in adult participants with CF, using a BMI cut-off of ≤18.5 kg/m2 to identify malnutrition led to classifying subjects with higher BMI values as well-nourished despite having inadequate fat free mass (Hollander et al 2014, King et al 2010). 

      For most nutrition assessment parameters examined (ex: handgrip strength, micronutrient deficiencies, lipid profile and Nutrition Focused Physical Exam), there was little or no evidence available in either the pediatric or adult CF population describing 1) validity and reliability compared to a reference standards (Academy of Nutrition and Dietetics Evidence Analysis Library, 2019) and 2) longitudinal relationship with mortality, FEV1 % predicted or quality of life (Academy of Nutrition and Dietetics, 2019). Therefore, it is unclear exactly how or how often these nutrition parameters should be assessed.

      Implementation. When assessing nutrition challenges and needs, RDNs must consider a host of other factors that may vary considerably between individuals with CF and will play an integral role in determining nutrition diagnosis and, consequently, nutrition intervention. For example, a large proportion of individuals with CF acquire CFRD over time, which, if not diagnosed or treated properly, is longitudinally associated with lung function decline and mortality (Goss et al 2018, Welsh et al 2014, Amadori et al 2009, Chamnan et al 2010, Vieni et al 2013, Hofer et al 2012). CFRD screening and management can prevent adverse effects associated with uncontrolled diabetes. Glucose homeostasis and insulin-related laboratory values must be carefully monitored and managed by the RDN with the interdisciplinary CF healthcare team, to prevent diabetes-related complications. In addition, RDNs must be aware of changing trends in CF that may need to be regularly considered during nutrition assessment, such as increasing rates of overweight in the CF population (Cystic Fibrosis Patient Registry 2017) or use of newly developed medications.

      The desirable effects of consistent, comprehensive nutrition care are likely to be large. Standardized clinic protocols and procedures are helpful to assure that accurate and timely prerequisite measurements and laboratory tests are available. As life expectancy projections increase (Keogh et al 2018), nutrition assessment is key for adapting to the evolving nutrition challenges that present in an individual with CF throughout a lifetime. The recommendations for nutrition assessment reflect current practice in most accredited CF centers. MNT should be incorporated into overall interdisciplinary clinical care and conducted in partnership with families and individuals with CF.

      Components of Comprehensive Nutrition Assessment. For individuals with CF, when conducting nutrition assessment to determine if and what nutrition interventions are necessary, RDNs should evaluate:


      • Growth parameters: Pediatrics
        • Conducted at each clinic visit
        • Infants < 2 years: Head circumference percentiles and z scores, weight-for-age weight-for-length, length-for-age percentiles and z scores using WHO growth charts
        • Pediatrics (≤18 years): Weight-for-age percentiles and z scores; height-for-age percentiles and z scores; BMI-for-age for children 2 years and older using CDC growth charts and weight status categories (Division of Nutrition 2019)
        • When possible, biological parental height should be considered, or adjusted for, when evaluating linear growth (EBMcalc 2019, Tanner et al 1970)
        • CF Centers and team members should collaborate to determine strategies for Tanner staging for adolescents, since self-reports can be inaccurate and Tanner exams can seem invasive.
      • Weight parameters: Adults
        • Adult (> 18 years): Weight, height and BMI using CDC weight status categories (Division of Nutrition 2019)
      • Body composition (please see Body Composition Assessment section for details)
        • Conducted during each nutrition assessment
        • fat mass, fat free mass, andbone mineral density according to external guidelines (please see Recommendation Overview Table)

      Biochemical (Please see “Nutrition Assessment of Biochemical Values” section for details)

      • Glucose homeostasis measures, such as response to OGTT.
        • Continuous glucose monitoring systems are not indicated for diagnosis of CFRD but may be ordered by an endocrinologist and data can be utilized by RDNs to guide nutrition care.
      • Fat soluble vitamins status including for levels of Vitamins A, D3 (25-OH-D) and E as well as prothrombin time (PT) for vitamin K)
      • Lipid profile, as indicated (National Center for Chronic Disease Prevention and Health Promotion 2019, American Academy of Pediatrics 2016)
      • Basic metabolic profile including sodium (Na), chloride (Cl), potassium (K), BUN, glucose, and liver enzyme levels
      • Urine sodium, as indicated (Borowitz et al 2002)


      • Pulmonary function, including FEV1% predicted and pulmonary exacerbations
      • Lung transplant and other medical history
      • Pancreatic insufficiency and pancreatic enzyme replacement therapy
      • Other medications that may alter nutrient intake or needs, such as appetite stimulants, growth hormones, insulin and/or CFTR modulation therapy
      • Gastrointestinal symptoms (constipation, symptoms of malabsorption including diarrhea/steatorrhea, DIOS, GERD, small intestinal bacterial overgrowth, C. difficile infection)
      • Co-morbidities, including CF-related diabetes, CF- related liver disease, CF-related bone disease, gallbladder/kidney issues, sinus disease or other gastrointestinal comorbidities such as Celiac Disease or inflammatory bowel disease
      • Nutrition focused physical exam (Academy of Nutrition and Dietetics, 2016)


      • Dietary intake history, including meal patterns. Quantitative assessment of dietary intake, including energy intake, may be assessed at least annually
      • Nutrient requirements, including energy expenditure using indirect calorimetry or appropriate prediction equations (please see section Assessment of Energy Requirements)
      • Eating environment and challenges for the individual with CF and family, including level of food security and access to resources to implement RDN recommendations
      • Values/beliefs related to dietary choices (ex: vegetarian, vegan, religious observations)


      • Beliefs about the impact of nutrition status on CF disease progression
      • Nutrition goals for the person with CF and family, such as weight status goals, dietary intake goals, reduction of nutrition-related symptoms or improved body image
      • Social determinants of health
      • Values and beliefs about food and nutrition

      Medical nutrition therapy follows the Nutrition Care Process (NCP) model, which directs how a client moves through nutrition assessment to nutrition intervention (Swan et al 2017). In the NCP, the RDNs will organize data collected by nutrition assessment and reassessment for comparison with defining characteristics of suspected diagnoses. RDNs should look for patterns and relationships among collected data to determine diagnoses, identify etiology that may be impacted by intervention, and identifying signs or symptoms that can be measured to determine progress during reassessment (Swan et al 2017) Following comprehensive nutrition assessment, the RDN should work with the individual, family and interdisciplinary health care team to determine health care priorities, including nutrition priorities. Nutrition goals and management should be integrated into overall plan of care. When determining primary nutrition goals following diagnosis, RDNs should consider not only disease pathology and biological characteristics, but also current dietary intake, cultural factors, psychosocial needs, the patient’s/family’s goals and preferences, lifestyle and mental and emotional health. RDNs are poised to translate assessment findings into individualized education and counseling, in order to co-produce a nutrition care plan that works for the individual with CF. As more information is gathered, nutrition diagnoses may evolve, dictating a modification to the treatment plan.

    • Recommendation Strength Rationale

      Evidence describing the effect of MNT protocols on outcomes was based on Grade III evidence. Evidence describing the relationships between nutrition parameters and hard outcomes was Grades I-III. However, the “effect” of nutrition assessment is difficult to gauge in studies, since it is the first step in Nutrition Care Process and subsequent steps also affect nutrition-related outcomes. Therefore, the evidence was also supported by clinical expertise. Suggested frequency of nutrition assessment contacts is based on general nutrition practice as well as clinical experience, guidance from the CF Foundation (Stallings et al 2008) and quality improvement or comparative studies (Ledger et al 2013, Stark et al 2011, Savant et al 2014, Ramirez et al 2015).

    • Minority Opinions

      Consensus reached.