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Educational Objectives:

After evaluating this article participants will be able to:

1. Implement strategies to avoid missing the nuances of sickle cell trait-related consequences
2. Recognize the populations potentially effected by sickle cell trait and include this diagnosis in the differential of such patients
3. Incorporate diagnostic strategies into clinical practice to assess patients at risk for sickle cell trait complications

 

It’s late on a Thursday evening shift and you pick up your next chart: A 34-year-old African-American female, pregnant at 16-weeks with intermittent cough for a few weeks. When you get to past medical history, she says to you, “Doctor, I have the sickle cell.” Your eyebrows raise as the complications of sickle cell disease run through your mind. “You mean the disease?” you clarify. “No, I have sickle cell trait,” she explains.

altSickle cell trait is the genetic pattern where a patient has inherited a normal hemoglobin gene (HbA) from one parent and an abnormal, mutated β1-globin gene, the sickle hemoglobin gene (HbS) from the other. Patients with sickle cell trait are commonly seen in EDs. In fact, 300 million people carry the sickle cell trait, most commonly in Africa and the Mediterranean. In the U.S., 1 in 12 African Americans have it and surprisingly, 1 in 413 Caucasians also carry the trait.

Ho hum, you assume. When patients offer a history of sickle cell trait, you don’t think about managing them any differently in the ED. Sickle cell trait is a non-disease, you think, except in its mild protective effect against malaria. Should we care?

Well, it depends on why they are in the ED. For many complaints, sickle cell trait is and should be treated as a non-disease. In fact, patients with sickle cell trait live just as long as those without it. Blood hemoglobin levels, other markers of red blood cell function and the interpretation of them are no different.

altBut biochemically, under conditions of severe tissue hypoxia, acidosis, increased viscosity, dehydration and hypothermia, sickle cell trait is actually associated with increased red blood cell sickling and polymerization. This often does not typically present as the classic complaints of sickle cell disease such as acute chest syndrome, painful crises or severe hemolytic anemia. But this becomes important because the aberrant tissue physiology causing polymerization commonly does result in a visit to the ED in patients with sickle cell trait.

One example is exercise-related death, which has been directly related to sickle cell trait. This is observed in U.S. army basic training camps, where recruits with sickle cell trait have a 30 fold higher risk of exercise-related death, when controlling for other pre-existing diseases.1 Early signs may include metabolic derangement from rhabdomyolysis or electrolyte disturbances such as hypernatremia or hyperkalemia in those who survive long enough to receive ED care. In sickle cell trait patients ill enough to require transfer to the ED for heat or exercise-related illness, you might consider checking electrolytes and their creatine kinase.

Another example is splenic infarction, which can occur in people with sickle cell trait at high altitudes, with heavy exercise and with other conditions that cause hypoxemia. The ED presentation of splenic infarction includes severe abdominal pain in the left upper quadrant, coupled with nausea, vomiting and sometimes a left sided pleural effusion. While patients with symptoms this severe may get a CT anyway, adding splenic infarction to your differential in patients with sickle cell trait could reduce your threshold for a definitive test in this population.

Hematuria also occurs more commonly in patients with sickle cell trait, presumably due to renal papillary necrosis from microscopic infarction in the kidney. While hematuria is commonly encountered in the ED, the management won’t likely differ in patients with or without sickle cell trait, except you may have a lower threshold to consider renal failure and order a serum creatinine. Other kidney diseases including polycystic kidney disease and renal medullary carcinoma are also more frequent in people with sickle cell trait. However, higher risk for these uncommon diseases may not change management, except as some clinicians may consider lowering their threshold to order a creatinine or refer patients for abdominal imaging not indicated for the average patient with hematuria.

A more common and important consideration is the diagnosis of pulmonary embolism (PE) in patients with sickle cell trait. Studies have found an association between PE and sickle cell trait in large administrative datasets.2,3 While sickle cell trait is not a true risk factor for PE confirmed by well controlled trials, it should be a consideration when evaluating low-risk patients.
 

Asymptomatic bacteriuria in pregnant patients, and urinary tract infections in general, also occur at higher rates in patients with sickle cell trait.4 In our fictional pregnant patient (an otherwise healthy pregnant woman), dipping the urine or sending it for urinalysis may be a prudent screening test even in the absence of urinary complaints. While some could argue that this sort of screening may not be our role, treating asymptomatic bacteriuria has proven benefits. It reduces the risk of pyelonephritis and lowers the risks of low birth weight and pre-term birth.5

So ultimately, how we should treat people with sickle cell trait really depends upon their presenting complaint. In fact, for many ED patients, it probably doesn’t matter. But it’s easy to get burned by the ones that do.

Jesse M. Pines, MD, MBA, MSCE is an associate professor of emergency medicine and health policy at the George Washington University Center for Healthcare Quality.


References:
1. Kark JA, Ward FT. Exercise and hemoglobin S. Semin Hematol 1994; 31:181-225.
2. Heller P, Best WR, Nelson RB, Becktel J. Clinical implications of sickle-cell trait and glucose-6-phosphate dehydrogenase deficiency in hospitalized black male patients. N Engl J Med. 1979;300:1001-5.
3. Austin H, Key NS, Benson JM, Lally C, Dowling NF, Whitsett C, Hooper WC. Sickle cell trait and the risk of venous thromboembolism among blacks. Blood. 2007;110:908-12.
4. Tsaras G, Owusu-Ansah A, Boateng FO, Amoateng-Adjepong Y. Complications associated with sickle cell trait: a brief narrative review. Am J Med. 2009 Jun;122(6):507-12
5. Villar J, Widmer M, Lydon-Rochelle MT, Gulmezoglu AM, Roganti A. Duration of treatment for asymptomatic bacteriuria during pregnancy. Cochrane Database Syst Rev. 2000;(2):CD000491.
     

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