By Renee DiIulio

Without oxygen, we would all die. Without hemoglobin, the protein that helps transport oxygen throughout our bodies, we would still die. With malfunctioning hemoglobin, as in the case of patients diagnosed with sickle cell disease (see Sidebar), we may not die right away, but our life expectancy is significantly shorter.

According to results from a study published in 1994, male patients with sickle cell anemia had an average life expectancy of 42 years; for females, it was 48 years.1 Among those with sickle cell-hemoglobin C disease, the median age at death was 60 years for males and 68 years for females.1 The life expectancy for a normal adult in 1994, according to the National Vital Statistics Reports, was 75.7 years of age: 72.4 years for males and 79.0 years for females.2

Clearly, sickle cell disease takes a toll on patients that starts at a young age. Newborns may be protected from painful episodes by their level of fetal hemoglobin. However, by age 4 months, symptoms can begin to manifest. Children with sickle cell disease have an increased risk of infections and related mortality.

“Pediatric patients are more prone to pneumonia and infections, which can lead to a high mortality rate,” says Dorothy Moore, MD, chief medical officer of the Sickle Cell Disease Association of America Inc (SCDAA of Baltimore). If treatment of sickle cell disease is begun early, these complications can be reduced or even avoided. It therefore behooves us to screen for the disease in newborns, she says. All but three states now require such screening (see Sidebar).

Screening, an area in which the laboratory plays a major role, has been one of the advances made in the management of this condition. The clinical lab is responsible for running the tests that determine whether a patient has sickle cell disease and, if so, what type. There is no gold standard, but two tests have been relied on for years and are often used together to confirm a diagnosis: hemoglobin electrophoresis and high-performance liquid chromatography (HPLC). Labs also play a role throughout treatment, helping to monitor patients for complications resulting from the disease or medication.

Affecting Lives
Sickle cell disease does not impact the same number of people as the leading killers, such as heart disease and cancer, but it does affect roughly 72,000 Americans, according to National Institutes of Health (NIH of Bethesda, Md).3 Thought to confer resistance to malaria, the condition is more common in people whose families come from certain regions of Africa, South America, Cuba, and Central America; Saudi Arabia; India; and Mediterranean countries, such as Turkey, Greece, and Italy.3 In the United States, the disease occurs in about one in every 600 African-American births and one in every 1,000–1,400 Hispanic-American births (3). Sickle cell trait is more frequent. About 2 million Americans carry the trait; about one in 12 African-Americans carry it.3

Despite its higher incidence in certain ethnic groups, it is recommended that all infants be tested. Infants and young children, especially, are susceptible to bacterial infections that can kill them in as little as 9 hours from the onset of fever. Pneumococcal infections used to be the principal cause of death in children with sickle cell anemia until physicians began routinely giving penicillin on a preventive basis to those who are diagnosed at birth or in early infancy.4

The American Academy of Family Physicians (AAFP of Leawood, Kan) notes in a study published in 1986 by Gaston et al that in a double-blind, randomized, placebo-controlled trial, there was an 84% reduction in the incidence of pneumococcal sepsis, the most serious complication of sickle cell anemia in young infants, when prophylactic oral penicillin was initiated by the age of 3 months.5

Extending Lives
Accurate screening is therefore key to reducing mortality related to sickle cell disease, particularly in young patients. “So much rides on the screening that it’s important for labs to keep false results to a minimum,” says Michael R. DeBaun, MD, MPH, associate professor of pediatrics and an attending physician in the division of hematology-oncology at the Washington University School of Medicine (St Louis). “A false positive is not that bad, but a false negative is problematic,” he adds.

False negatives are difficult to determine, notes DeBaun. “If patients are missed, then we may not know if or when they develop the disease,” he says. No confirmatory test is run for a negative result.

Positives are typically confirmed with typing of the disease. “When abnormal results are indicated, the results must be confirmed,” says DeBaun of the newborn screenings. “The clinician gathers medical history, and the test is often repeated in another lab,” he says.

“Typically, confirmation is determined with a DNA-based technique,” says Martin Steinberg, MD, professor of medicine, pediatrics, pathology, and laboratory medicine at the Boston University School of Medicine (Boston). He notes that running multiple tests is extremely reliable in diagnosing and typing the disease.

Diagnosing Lives
Several screening methodologies are acceptable, but there is no gold standard. Tests include hemoglobin electrophoresis, isoelectric focusing, HPLC, and/or genetic testing. DNA analysis provides the most accurate diagnosis in patients of any age, but it is still relatively expensive.5 “In general, these tests have comparable accuracy. The testing method should be selected on the basis of local availability and cost.”5

“Newborn screening methods typically use electrophoresis, HPLC, or both in conjunction. Either or both is fine,” says DeBaun. Both methods can distinguish between types of the disease as well as sickle cell trait by measuring the amount and type of hemoglobin in the blood. Moore recommends that electrophoresis tests be run with both an acid base and a cellular base to more accurately determine the presence of trait.

The most important role played by the lab, according to DeBaun, is determination of type. “All sickle cell syndromes are determined by the lab, not only with hemoglobin analysis but also with CBCs [complete blood counts]. Using a smear, technologists can look at the number, type, and morphology of sickle cells, which also helps to determine a diagnosis,” says DeBaun.

Other tests run, particularly in adults, may include reticulocyte counts, differential white blood cell counts, liver function, and tests for BUN, creatine, and serum electrolytes. What should not be run, especially in newborns, is a solubility test.

“I don’t recommend solubility testing as a diagnostic test in anyone. It should never be relied on, but particularly in newborns, because of the high level of fetal hemoglobin,” says Steinberg. Moore agrees that it has no value in determining type, and DeBaun adds that it has “almost no clinical benefit.”

More certain benefit can be derived from genetic testing. When a newborn is diagnosed with sickle cell trait or disease, the parents can gather further insight with testing of their DNA. In addition, eggs and the fetus can be tested.

“We can now test in utero to determine if a fetus has sickle cell. We can also test eggs before they are implanted to select healthier eggs,” says Moore.

Impacting Lives
Unfortunately, there is no diagnostic measure for a painful episode. “There is no method to diagnose a painful episode, and that is part of the problem in treatment. There’s no measure of the intensity of the pain to validate it. We must take the patient’s word, and this can be a hindrance,” says Moore.

DeBaun agrees that painful episodes are limited to subjective observation. “We must trust that the patient is feeling pain,” says DeBaun.

Painful episodes are often treated with pain management and fluids, but some patients may take hydroxyurea, which has shown some success in minimizing episodes. “Hydroxyurea is used mainly to treat adults, but it is commonly used in children 10 years and older. The drug is beneficial to most, but it needs to be monitored. The lab will perform frequent CBCs, liver, and kidney tests, as well as tests to measure fetal hemoglobin and ensure that it is actually increasing,” says Steinberg.

Other patients may opt for blood transfusions, though this is not as common since matching donors are difficult to find. “In patients getting blood transfusions, particularly chronic transfusions, we must test for antibodies and items of that nature. We must monitor iron to prevent overload, which can negatively affect the heart and liver. And we must keep track of the patient’s general health. Sickle cell disease has a negative impact on many organs,” says Moore.

The biggest challenge, though, according to Steinberg, is looking for the disease and making the diagnosis. “There are multiple lab tools, from taking a clinical history to performing blood counts to viewing lab films to measuring hemoglobin fractions with HPLC. If we do the right things, the diagnosis is almost always 100-percent accurate,” says Steinberg. When done early enough, it can save small lives.

The ABCs of Sickle Cell Disease
Sickle cell disease is an autosomal recessive disorder that impacts the production of hemoglobin, the protein that makes up roughly 90% of a red blood cell. Hemoglobin gives blood its color and function. Responsible for transporting oxygen and carbon dioxide throughout the body, its presence in the cells keeps them soft, disc-shaped, and flexible.

Normal adults carry hemoglobin A. Those affected with sickle cell disease carry a different, malfunctioning form, such as hemoglobin S or hemoglobin C. There are several types of the disease, but in most, the wrong hemoglobin can cause the cells to sickle, making them crescent-shaped and rigid.

The deformed and inflexible cells can get trapped in small blood vessels, blocking them, slowing the blood flow, causing pain, and damaging tissues and organs. Repeated crises, known as painful episodes, can be life-threatening both in the near and short term, particularly for infants. They can damage the kidneys, lungs, bones, eyes, and central nervous system, as well as increase the risk of infections. Episode frequency varies with the patient and specific condition, which is related to the type of hemoglobin produced by the body.

The genetic mutation responsible for the disease is believed to be located on the 11th pair of chromosomes within coding for hemoglobin. If both chromosomes are affected, the patient will likely develop some form of sickle cell disease. If only one of the chromosomes carries the mutation, the patient has sickle cell trait. Carriers of the trait produce both hemoglobin A and hemoglobin S; hence, the condition is sometimes referred to as hemoglobin AS. Because they typically carry more hemoglobin A than S, these patients tend to experience few if any symptoms. However, certain conditions, such as dehydration or severe infection, can cause sickling of the red blood cells.

Some of the other common variations of sickle cell disease are:

•    Sickle cell anemia: Also known as hemoglobin SS, this condition is one of the more serious sickle cell diseases. With nearly all of their hemoglobin A replaced with hemoglobin S, these patients can experience many complications, including chronic and severe anemia.

•    Sickle cell-C disease: Hemoglobin SC patients carry both hemoglobin S and hemoglobin C. Though anemia is not quite as pronounced, these patients may still suffer from painful episodes.

•    Sickle cell-E disease: Patients with this condition have another different element in their hemoglobin, but the variation is similar to sickle cell-C. Some may experience no symptoms.

•    Sickle cell S-beta-thalassemia: Though symptoms may be milder than those of sickle cell anemia, these patients may still experience anemia and painful episodes.
Screening States
In 1987, the National Institutes of Health (NIH of Bethesda, Md) published a consensus statement in which it urged that screening for sickle cell disease in newborns be universal. Many of those states that did not already check for the disease have since added it, leaving only three states that do not require newborn screening for sickle cell disease or hemoglobinopathies. These states, according to information compiled on the Save Babies Through Screening Foundation Inc (Malvern, Pa) Web site, do not require sickle cell screening: Idaho, Montana, and New Hampshire. Montana, however, has a pilot study screening program under way.

Renee DiIulio is a contributing writer for Clinical Lab Products.

References
1. Platt OS, Brambilla DJ, Rosse WF, et al. Mortality in sickle cell disease. Life expectancy and risk factors for early death. N Engl J Med. 1994;330(23):1639–1644.
2. National Center for Health Statistics. National Vital Statistics Report. 2004; 53(6). Available at http://www.cdc.gov/nchs/about/major/dvs/mortdata.htm.   Accessed July 18, 2005.
3. National Heart, Lung, and Blood Institute/National Institutes of Health. Who gets sickle cell anemia? 2003. Available at http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_WhoIsAtRisk.html.    Accessed July 18, 2005.
4. US Department of Energy, Biological, and Environmental Research/Human Genome Project Information. Genetic disease profile: sickle cell anemia. Available at http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/sea.shtml.   Accessed July 18, 2005.
5. Wethers DL. Sickle cell disease in childhood: part I, laboratory diagnosis, pathophysiology, and health maintenance. Am Fam Physician. 2000 Sep 1;62(5):1013–1028. Available at http://www.aafp.org/afp/20000901/1013.html.   Accessed July 18, 2005.