Is sickle cell crisis a valid measure of clinical severity in sickle cell anemia?

We studied the conditional probability of developing a sickle cell crisis in 509 patients with sickle cell anemia (SS), with variable number of prior crises. These SS patients were followed during different calendar eras, having diverse complications, and had entered and/or lost to follow-up at different ages. The probability of having a sickle cell crisis during the first three decades of life increases significantly with the number of prior crises episodes (p less than 0.001). After more than five cryptogenic crises, the patient has developed a patterned response to stress that overshadows other influences, such as the effects of therapeutic agents, thus lessening the 'power' of sickle crisis as a measure of morbidity.