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Table 1 Example of the patient-important consequences of being classified into TP, TN, FP, and FN categories

From: Application of GRADE: Making evidence-based recommendations about diagnostic tests in clinical practice guidelines

Question 1: Should skin prick tests be used for the diagnosis of IgE-mediated CMA in patients suspected of CMA?
Population Patients suspected of cow's milk allergy (CMA)
Intervention: Skin prick test (SPT)
Comparison Oral food challenge (OFC)
Outcomes  
   TP The child will undergo OFC, which will turn out positive with risk of anaphylaxis, albeit in controlled environment; burden on time and anxiety for family; exclusion of milk and use of special formulae. Some children with high pre-test probability of disease and/or at high risk of anaphylactic shock during the challenge will not undergo challenge test and be treated with the same consequences of treatment as those who underwent food challenge.
   TN The child will receive cow's milk at home with no reaction, no exclusion of milk, no burden on family time and decreased use of resources (no challenge test, no formulae); anxiety in the child and family may depend on the family; looking for other explanation of the symptoms.
   FP The patient will undergo an OFC, which will be negative; unnecessary burden on time and anxiety in a family; unnecessary time and resources spent on oral challenge. Some children with high pre-test probability of CMA would not undergo challenge test and would be unnecessarily treated with elimination diet and formula that may led to nutritional deficits (e.g., failure to thrive, rickets, Vit D or calcium deficiency); also stress for the family and unnecessary carrying epinephrine self injector which may be costly as well as delayed diagnosis of the real cause of symptoms.
   FN The child will be allowed home and will have an allergic reaction (possibly anaphylactic) to cow's milk at home; high parental anxiety and reluctance to introduce future foods; may lead to multiple exclusion diet. The real cause of symptoms (i.e., CMA) will be missed leading to unnecessary investigations and treatments.
Inconclusive results Either negative positive control or positive negative control: the child would repeat SPT which may be distressing for the child and parent; time spent by a nurse and a repeat clinic appointment would have resource implications; alternatively, child would have sIgE measured or undergo food challenge
Complications of a test SPT can cause discomfort or exacerbation of eczema that can cause distress and parental anxiety; food challenge may cause anaphylaxis and exacerbation of other symptoms.
Resource utilization (cost) SPT adds extra time to clinic appointment however; OFC has much greater resource implications
  1. TP - true positive (being correctly classified as having CMA), TN - true negative (being correctly classified as not having CMA), FP - false positive (being incorrectly classified as having CMA), FN - false negative (being incorrectly classified as not having CMA); these outcomes are always determined in comparison with a reference standard (i.e., food challenge test with cow's milk)