Letters to the Editor

Genetic Counseling in Preconception Health Care

TO THE EDITOR: Dr. Brundage's article, "Preconception Health Care,"¹ is most informative and covers a broad range of issues. However, I would like to address the comments made in Table 2, which was titled "Carrier Screening by Ethnicity."

If a woman of black, Southeast Asian, or Mediterranean ancestry would be interested in the prenatal diagnosis of a clinically important hemoglobinopathy (sickle cell disease, hemoglobin SC disease, sickle/thalassemia disease), the recommendation of the American College of Obstetricians and Gynecologists (ACOG) is that both the mean corpuscular volume and the hemoglobin electrophoresis should be determined.²

In addition to screening for Tay-Sachs disease, the current recommendation by ACOG is that carrier testing for Canavan's disease should also be offered if both parents are of Ashkenazi Jewish ancestry. If only one partner is of Ashkenazi Jewish descent, this partner should be screened first.³ There are other disorders, occurring more frequently in the Ashkenazi Jewish population, for which carrier testing is also available.

As Dr. Brundage pointed out, carrier testing for cystic fibrosis (CF) is addressed by the joint ACOG/American College of Medical Genetics and the National Human Genome Research Institute consensus conference. The committee recommended offering CF screening to persons with a family history of CF, reproductive partners of people who have CF, and white couples who are planning a pregnancy or seeking prenatal care. It also recommends that screening should be made available to couples in other racial and ethnic groups.⁴ ACOG has a good patient information brochure available on CF.

Genetic counselors, certified by the American Board of Medical Genetics and the American Board of Genetic Counseling, are available to assist physicians and consult with couples about these and other issues. An extensive listing of genetic counselors in the United States and around the world can be found at the National Society of Genetic Counselors Web site (www.nsgc.org).

JODI K. RUCQUOI, M.S.
Director of Genetic Counseling
Greenwich Hospital
Yale New Haven Health Systems
5 Perryridge Road
Greenwich, CT 06830

REFERENCES

1. Brundage SC. Preconception health care. Am Fam Physician 2002;65:2507-14.
2. ACOG (American College of Obstetricians and Gynecologists) committee opinion. Genetic screening for hemoglobinopathies, number 238, July 2000 (replaces number 168, February 1996). Committee on Genetics. Int J Gynaecol Obstet 2001;74:309-10.
3. ACOG committee opinion. Screening for Canavan disease. Number 212, November 1998. Committee on Genetics. American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet 1999;65:91-2.
4. Grody WW, Cutting GR, Klinger KW, Richards CS, Watson MS, Desnick RJ. Laboratory standards and guidelines for population-based cystic fibrosis carrier screening. Genet Med 2001;3:149-54.

Assessment of Lactose Tests

to the editor: In the article, "Lactose Intolerance,"¹ Dr. Swagerty and colleagues acknowledge that the lactose tolerance test has false-positive or false-negative results in 20 percent of patients. They also state that the lactose breath hydrogen test has been found positive in 90 percent of patients with lactose malabsorption.

We compared three different methods of diagnosing lactose malabsorption: (1) lactose load with determination of blood glucose concentration; (2) lactose load with urinary galactose measurement; and (3) duodenal lactase activity assay. Our studies show a higher false-negative rate when using blood glucose measurements, causing lactose malabsorption to remain undiagnosed in many patients. The sensitivity and specificity in our studies was only 60 percent and 96 percent, respectively. The specificity is comparable with the use of breath hydrogen or urinary galactose measurement tests.^2,3 Therefore, the lactose test with blood glucose measurement should not be used as a screening test when high sensitivity is important.

When assessing the effectiveness of these tests in the clinical practice setting, one must consider predictive values as well as false-positive and false-negative results. Although the sensitivity and specificity of the test can be the same, positive and negative predictive values depend on the pretest probability or disease prevalence. For example, our studies produced an increase in the positive predictive value from 82 percent among a general Estonian population with a lower lactose malabsorption prevalence of 23 percent, to 95 percent among a Russian population in Estonia with a high lactose malabsorption prevalence of 57 percent, to 99.5 percent among a Khanty population in Siberia with a lactose malabsorption prevalence of 83 percent.^4,5 If the test is used among patients with an increased pretest probability of lactose malabsorption (e.g., patients reporting milk intolerance), the positive predictive value of the test is higher than in the general population.

In clinical practice, it is important to accept that clinical intolerance to lactose may not be synonymous with low lactase activity. When the diagnosis is confirmed by lactose testing, we prefer to speak about lactose malabsorption because our experience from hundreds of tests among the general population shows that approximately 30 percent of patients with lactose malabsorption can clinically tolerate lactose without any symptoms.

MARGUS LEMBER, M.D.
Department of Internal Medicine
University of Tartu, Estonia

REFERENCES

1. Swagerty DL Jr, Walling AD, Klein RM. Lactose intolerance. Am Fam Physician 2002;65:1845-50.
2. Arola H, Koivula T, Jokela H, Jauhiainen M, Keyriläinen O, Uusitalo A, et al. Strip test is reliable in common prevalences of hypolactasia. Scand J Gastoenterol 1987;22:509-12.
3. Lember M, Tamm A, Maaroos H, Suurmaa K. Diagnosis of primary hypolactasia by duodenal lactase activity. Eur J Gastroenterol Hepatol 1993; 5:511-3.
4. Lember M, Tamm A, Villako K. Lactose malabsorption in Estonians and Russians. Eur J Gastroenterol Hepatol 1991;3:479-81.
5. Lember M, Tamm A, Piirsoo A, Suurmaa K, Kermes K, Kermes R, et al. Lactose malabsorption in Khants in western Siberia. Scand J Gastroenterol 1995;30:225-7.

FIGURE 1. Two forms of electrosurgery: (A) Electrodesiccation with an active electrode tip touching the skin and showing penetration of planned tissue damage. (B) Fulguration with sparking from electrode to tissue. Treatment area is more superficial than in desiccation.

Corrections

The article "Prealbumin: A Marker for Nutritional Evaluation" (April 15, 2002, page 1575) contained an error in the daily measurement of kilocalories administered via percutaneous endoscopic gastrostomy (PEG) tube feeding. On page 1577, in the second paragraph under the subheading "Illustrative Case," the second sentence should read: PEG tube feeding was commenced at 1,700 kcal per day.

The article "Electrosurgery for the Skin," (October 1, 2002, page 1259) contained an error in the labeling of Figure 1 on page 1260. Part A of Figure 1 was incorrectly identified as part B, and vice versa. The artist's name was omited. The correct figure and figure legend are printed below.

Send letters to Jay Siwek, M.D., Editor, American Family Physician, 11400 Tomahawk Creek Pkwy., Leawood, KS 66211-2672; fax: 913-906-6080; e-mail: afplet@ aafp.org. Please include your complete address, telephone number, and fax number. Letters should be submitted on disk, double-spaced, fewer than 500 words, and limited to one table or figure and six references. Please submit a word count. Letters submitted for publication in AFP must not be submitted to any other publication. Possible conflicts of interest must be disclosed at time of submission. Submission of a letter will be construed as granting the AAFP permission to publish the letter in any of its publications in any form. The editors may edit letters to meet style and space requirements.