The magic in the numbers

In Western medicine, health care providers often rely on bodily fluids such as blood and urine to assess our overall wellness, or to diagnose a disease process. A standard blood panel is usually an element of an annual physical exam that, hopefully, everyone does as a wellness “progressive maintenance” program. The results of these labs provides the treating physician with vital cues of what looks good and what needs some attention.

The FAA uses these same tools to do risk assessment for medical certification purposes, too. It is very common for pilots with a cardiac history to be asked to provide a lipid profile and fasting blood glucose, for example, as part of their special issuance evaluations. The labs that perform these tests have established “normal values” for each test, and the FAA typically expects these values to be somewhere near the normal range, but not necessarily “in” the normal range. Keep in mind that different labs may have slightly different ranges of normal, so for that reason, the FAA may have a little “wiggle room” for medical certification purposes.

For example, that lipid profile usually includes total cholesterol; HDL (high density lipoprotein), the “good cholesterol”; LDL (low density lipoprotein), the “bad” form; and triglycerides. There also may be an HDL/LDL ratio that usually isn’t considered as important a number to keep in mind for medical certification purposes. The FAA pays more attention to the high limits for lipids, and doesn’t usually get too excited about total cholesterol until the number hits 300. Higher than that, and a denial of certification is likely, especially for cardiac certification because modification of risk factors, including lipids, is important to slow the progression of heart disease. Triglycerides can be as high as 400, while LDL should be under 180. HDL, the scavenger lipid protein that gobbles up the low-density lipoproteins, has no upper limit for certification. Higher is better for HDL.

Diabetes is also a risk factor and “comorbidity” of heart disease, so fasting blood sugar is part of the lab panel, too. Maximum fasting blood sugar is 140. The A1C hemoglobin, a calculation of blood sugar over about nine weeks, is expressed as a percentage, and 6.5 percent is about as high as the FAA will allow for cardiac certification.

Another important number for pilots who take warfarin, or Coumadin, a blood thinning drug, is the international normalized ratio (INR). Anticoagulants are prescribed for a number of medical conditions, and the INR range is different depending upon the condition being treated. Generally, the INR range is 2.0 to 3.0 for treatment of deep vein thrombosis, pulmonary embolism, and bioprosthetic heart valve prostheses. That number is slightly higher, 2.5 to 3.5, for mechanical heart valves.

For certain types of blood disorders, such as anemias, the hematocrit and hemoglobin are important numbers to watch. Hematocrit represents the percentage of red blood cells by volume in whole blood, and hemoglobin is a protein that moves oxygen throughout the body. These numbers very slightly between males and females, but hemoglobin should be between about 13.5 and 18 for men, and 12 to 16 for women. Hematocrit falls in the 45 ti 62 percent range for men, and 37 to 48 percent for women. Hemoglobin levels that fall below 10 indicate a problem, and denial of certification is almost certain because of the loss of oxygen-carrying capacity with levels that low. Low hemoglobin can have a number of causes, so a good workup with your treating doctor would also be needed.   

Portrait of Gary Crump, AOPA's director of medical certification with a Cessna 182 Skylane at the National Aviation Community Center.
Frederick, MD USA
Gary Crump
Gary is the Director of AOPA’s Pilot Information Center Medical Certification Section and has spent the last 32 years assisting AOPA members. He is also a former Operating Room Technician, Professional Firefighter/Emergency Medical Technician, and has been a pilot since 1973.
Topics: Emergency, Training and Safety

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