Isaiah Laurencin, the Miramar football player who collapsed after football conditioning drills in July, died of multiple natural causes, one of which was sickle cell trait, according to the Broward County Medical Examiner’s Office.

In his five-page autopsy report, Dr. Robert Buchsbaum wrote that Laurencin died as “a result of cardiac arrest during physical exertion due to multiple factors superimposed upon sickle cell trait and alpha thalassemia.”

Alpha thalessemia is an inherited blood disorder that leads to abnormal red blood cells and anemia.

The report also cited hypertension, bronchitis and high temperatures during prolonged football practice as “co-morbid natural factors.” The report said that none of those factors, including the sickle cell trait, was the single reason Laurencin died.

Obesity was cited in the report. Laurencin was 6-foot-1 and weighed 286 pounds. The report also stated that Laurencin had clinical history indicating that he had a heat stroke a year before his death.

Laurencin, 16, died July 27 after collapsing at an offseason football conditioning workout. Miramar players dedicated the season to him, and won 13 consecutive games, not losing until the Class 8A state championship.

At least 17 high school and college athletes’ deaths have been tied to sickle cell trait during the past 11 years. The group includes Olivier Louis, a player at Wekiva High School near Orlando, who died on Sept. 7, 2010, after his first football practice.

Miramar held two offseason conditioning sessions a day during the summer. The sessions were voluntary, but most team members participated. The morning session usually consisted of weightlifting, with the evening session — held during times of cooler temperatures — usually focusing on running and cardiovascular work.

The heat index reached as high as 99 degrees on July 26, but at the time of Laurencin’s collapse, it had fallen to about 92. Laurencin said he was not feeling well early in the day’s second workout, and was held out for most of it, according to Nadine Drew, spokeswoman for the Broward school district.

The autopsy report said Laurencin vomited and collapsed toward the end of the session, and was given water by bystanders before EMS personnel arrived at the school.

Laurencin was a big man with a calm, fun-loving demeanor, according to family members and friends. He was described as a class clown, but also as a football fanatic. His dream was to receive a scholarship to play major college football. Heading into his senior season, teammates said that they noticed a more focused and determined Laurencin, and he looked poised to fulfill his dream.

In July, Drew said that Laurencin had passed his most recent physical exam. The state pre-participation physical form expressly asks whether the student had been diagnosed with the sickle cell trait or sickle cell anemia. Drew said she did not know whether Laurencin had answered “yes” to either question or if the physical form on file was recently taken for the 2011 season.

Miramar principal Brian Faso declined comment on Wednesday “out of respect for the family.” Miramar football coach Damon Cogdell also declined to comment.

Multiple attempts to reach family members were unsuccessful.

Sickle cell trait is a debilitating blood disease that warps red blood cells and can cause strokes, fever and ulcers. The disease typically reduces a person’s lifespan.

People with sickle cell anemia have Hemoglobin S, a variant of two genes that cause flexible doughnut-shaped red blood cells to collapse into rigid crescents or sickles. The cells get sticky, block blood flow and can cause major organ damage.

People with sickle cell trait do not have sickle cell anemia.

Sickle cell trait carriers have Hemoglobin SA, with one gene capable of making warped red blood cells and one that produces normal red blood cells. Most people with the trait typically don’t suffer any symptoms or health problems related to the condition.

Sun Sentinel staff writer Iliana Limon contributed to this report.