From Medscape Medical News <http://www.medscape.com/news>  , Nick Mulcahy

 

Summer Heat Diminishes Accuracy of Colon Cancer Screening Test

	
		
			

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July 7, 2010 - Immunochemical fecal occult blood tests (iFOBTs) that take place in the summer are 17% less likely to be positive than those that occur in the winter, according to new research published online July 5 in Gut. 

Summertime heat, which can alter the chemistry of the hemoglobin in the fecal sample, is probably the cause, say the authors of the 8-year retrospective analysis of nearly 200,000 iFOBTs performed in Italy as part of a colorectal cancer screening program.

"Our results predict a higher rate of false-negative iFOBT results during the summer period," write the authors, led by Grazia Grazzini, MD, from the Cancer Prevention and Research Institute in Florence, Italy.

The false negatives also reduce the likelihood that an iFOBT will pick up a cancer or an advanced adenoma.

"During the summer, significant neoplasia will be missed, which will increase the number of interval cancers," said Dr. Grazzini in a press statement.

Time Delay Also Affects Results 

Recently, a study from the Netherlands indicated that a time delay in the return of iFOBTs was also associated with false-negative results (Int J Cancer. 2009;125:746-750).

iFOBTs are more susceptible to degradation than the traditional guaiac-based fecal occult blood test (gFOBT), explained the lead author of that study, Leo G.M. van Rossum, PhD, from the Radboud University Nijmegen Medical Center in the Netherlands.

Now, in an interview with Medscape Medical News, Dr. van Rossum elaborated on the differences between the 2 tests.

The problem of false negatives with the gFOBT in population-based screening is "very limited, if it exists at all," he said. The gFOBT, which detects the heme component of the blood, is more stable for 2 reasons, said Dr. van Rossum. "Because the heme part of hemoglobin is less susceptible to degradation and because it is a 'dry' test, degradation is slowed down," he explained.

However, iFOBTs detect globin, say the authors of the new study.

iFOBTs are "more analytically specific and have a much lower detection limit," but they typically use "wet" collection systems, write Dr. Grazzini and his coauthors. "Globin is even more susceptible to denaturation than heme" in wet collection systems, they say.

Dr Grazzini and colleagues believe their findings have "significant implications" for the organization of national screening programs. "New mechanisms will need to be considered, which will minimize the effect of seasonal temperature variations on positive rates," they write.

Dr. van Rossum noted that gFOBT is the test of choice among the national screening programs that currently exist. However, "many are considering a switch to iFOBT."

In the new study from Italy, the iFOBT OC-Sensor (Eiken, Tokyo, Japan) was used as a single-day test, with a positivity threshold of 100 ng/mL of hemoglobin.

Minimizing the Effect of Seasonal Variation 

The potential problem of degraded test results with iFOBT should not be a barrier to using this kind of test, suggested Dr. von Rossum.

The degradation "can and should be remedied by the design of the screening program," he said.

Dr. Grazzini and his coauthors provide a number of suggestions to minimize the effect of variations in temperature on the rate of false-negative test results. However, they acknowledge that such modifications might decrease participation and increase cost.

Some of the mechanisms that can be considered are:

*	sending samples to the laboratory immediately after collection 
*	storing samples in a refrigerator prior to transportation to the laboratory 
*	having individuals record the sample collection date and then exclude those that fall outside a designated "safe" period 
*	reducing the amount of transportation time between the participant and the laboratory 
*	refrigerating samples with ice packs during transport to the laboratory 
*	testing samples immediately upon receipt by the laboratory or refrigerating them upon receipt 
*	adopting a seasonal strategy, such as reducing the cut-off points from 100 ng/mL to 80 ng/mL or using a positive from either of 2 samples instead of a single sample during the summer period 
*	suspending screening activity during the warmest time of the year. 

Study Details 

This study is the first to suggest that seasonal variations in temperature might influence the performance of a screening program, say the authors.

A total of 199,654 iFOBTs were performed in the colorectal cancer screening program in the Florence district of Italy between January 2001 and December 2008.

Study participants, who were 50 to 70 years of age, were invited by mail every 2 years to perform a single iFOBT with no dietary restrictions. Subjects who tested positive were offered a full colonoscopy.

The iFOBTs were returned to local healthcare units by participants and stored at 4 °C (or at room temperature for a few hours) before being transported every 2 days to a centralized laboratory. Refrigeration of samples was recommended during transport. Once received by the laboratory, samples were stored at 4 °C.

The average time between test delivery date and analysis was 12.1 days.

According to the authors, the average ambient temperature during the study period was 16.0 °C in the spring, 25.1 °C in the summer, 14.0 °C in the autumn, and 7.9 °C in the winter.

There was a decrease in hemoglobin concentration with increasing temperature.

The mean hemoglobin concentration was 27.6 ng/mL (95% confidence interval [CI], 26.2 - 29.1) in the spring, 25.2 ng/mL (95% CI, 23.1 - 27.3) in the summer, 29.2 ng/mL (95% CI, 27.7- 30.6) in the autumn, and 29.5 ng/mL (95% CI, 27.9 - 31.1) in the winter (Kruskal-Wallis test for equality of rank; P < .001).

The study authors also report that in the summer, the probability of a positive result was 17% lower than in the winter (odds ratio, 0.83; 95% CI, 0.76 - 0.90).

The researchers have disclosed no relevant financial relationships. 

Gut. Published online July 5, 2010. 

 

 

Regards,

 

Steve

 

Steve Coward

Operational Manager, Automation

Clinical Biochemistry

Belfast Trust

028 9063 3007

 

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