What does diagnostic threshold mean? Deterministic and probabilistic considerations

Excerpt

A weather forecast of rain tomorrow is a dichotomic prediction, whereas a forecast that predicts a chance of rain is probabilistic as opposed to a prediction of either sunshine or rain is deterministic. When the probability of rain is 40%, precautions could include bringing an umbrella, or wearing a raincoat before going out, or both, or neither. The final choice of a subsequent action depends on having appropriate information. Although an approach based on probability is essentially included in the process of any medical decision, specific thresholds of normal and abnormal values are often applied. For example, anemia can be defined when hemoglobin values are < 12 and 13 g/dL in women and in men, respectively (though these values might differ slightly among laboratories). Heart-to-mediastinum (H/M) ratios of 1.6, 1.68, and 1.75 in ¹²³I-metaiodobenzylguanidine (mIBG) images might signal a poor prognosis for patients with heart failure.1‐3 Such thresholds are straightforward and help to guide subsequent actions in clinical practice; however, the question remains as to how appropriate thresholds are determined. …