Letters

Diagnosis of Creutzfeldt-Jakob disease by measurement of S100 protein in serum

BMJ 1998; 317 doi: https://doi.org/10.1136/bmj.317.7156.472 (Published 15 August 1998) Cite this as: BMJ 1998;317:472

Appropriate study populations must be used

  1. J P McConville, Specialist registrar in neurology, locum appointment training,
  2. J J Craig, Specialist registrar in neurology
  1. Royal Victoria Hospital, Belfast BT12 6BB
  2. Department of Neurogenetics, Imperial College School of Medicine at St Mary's, London W2 1PG
  3. St Mary's Hospital, London W2 1NY
  4. Neurologische Klinik und Poliklinik, Georg-August-Universität Göttingen, D-37075 Göttingen, Germany
  5. Psychiatrische Klinik und Poliklinik, Georg-August-Universität Göttingen, D-37075 Göttingen, Germany
  6. Georg-August-Universität, D-37075 Göttingen, Germany

    EDITOR—Otto et al describe significant differences in the serum concentrations of S100 protein in patients with and without Creutzfeldt-Jakob disease.1 The population of patients studied is, however, not appropriate for assessing the usefulness of measuring serum concentrations of S100 protein as a diagnostic test, and Otto et al's calculations of positive and negative predictive values of the test are invalid as they fail to take into consideration the prevalence of Creutzfeldt-Jakob disease as a cause of dementia.

    Patients with clinically evident disease do not need a diagnostic test. It is not informative to evaluate the potential of a blood test to distinguish those with clinically definite Creutzfeldt-Jakob disease from those without the disease on clinical grounds. The test is useful only if it helps to predict the likelihood of the disease in a population that does not meet the criteria for probable Creutzfeldt-Jakob disease, which is therefore the population in which it must be assessed.

    View this table:

    Sensitivity, specificity, and predictive values of serum concentrations of S100 protein in Creutzfeldt-Jakob disease (CJD) among patients with dementia. Predictive values are dramatically influenced by prevalence of target disorder within the population tested

    Otto et al say that the primary use of serum concentrations of S100 protein will be in the differential diagnosis of diseases that cause dementia. At a cut off of 213 pg/ml they calculate a sensitivity of 77.8% and specificity of 81.1% for detecting Creutzfeldt-Jakob disease in a referred population of 108 patients with definite or probable …

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