Unexpected Results - Understanding Your Hematocrit

By: Alere Staff

While no two people are alike, we all share the importance of blood for a happy and healthy life. Blood, in part, provides life by delivering oxygen to our tissues and organs, fighting germs, and stopping you from bleeding when you get injured. Blood has three parts to it: red blood cells, white blood cells and fluid between the cells to allow them to flow freely. Your white blood cells fight off bacteria, viruses and reduce your risk of infection while red blood cells carry oxygen keeping your body running smoothly.

Your body has an amazing way of keeping your blood in balance. If you get sick your body triggers an increase in white blood cell production to make you well again. Red blood cells are produced to meet the oxygen demands of your body.

Hematocrit or (Hct) is the proportion of whole blood volume that is made of red blood cells.This is also called packed-cell volume (PCV). Normal ranges of red blood cells include 40.7 to 50.3% for men and 36.1 to 44.3% for women.Low or high hematocrit counts can be caused by several health conditions or diseases. 

How is a Hematocrit Test Performed?

A hematocrit test is done in a lab. Using a sample of your blood a lab technician or hematologist uses a centrifuge that spins the blood, separating it into three parts: plasma (the fluid component), red blood cells and other blood cells. When the blood is separated, the count of red cells can be determined.

Effects of Hematocrit on INR Results

The use of Home INR Meters is not recommended for patients with a low Hct. Hematocrit is an important determinant of the accuracy of blood tests, thus anemia and other conditions associated with low hematocrit may affect the accuracy of the INR tests done both on an INR meter and by a lab.2 The studied range of hematocrit with the CoaguChek® device for example is between 22%-55%.3 Test procedures are designed to correct for an average hematocrit value in patient samples, yet data shows that this type of single correction done in the test is not sufficient to correct hematocrit in samples with values that have more than 10% difference and in those with high INRs. When the hematocrit value was 28- 32%, results were not necessarily impaired by low hematocrit counts.4 The sickest patients with high or low hematocrit values are therefore the most at risk for a clinically significant error.2

Be sure to have your hematocrit checked by your doctor. If you have been sick, experienced fluid loss or had intravenous (IV) fluid added to your blood, make sure you share this with your healthcare provided before your next blood test; it is important information your doctor will need to accurately measure your blood.

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References:

  1. Gersten M.D., T. Hematocrit. Medline Plus. February 24, 2014. Retrieved March 9, 2015 from web site: http://www.nlm.nih.gov/medlineplus/ency/article/003646.htm
  2. Bussey, Henry. Lab or POC INR Results - Which are more reliable? Retreived March 9, 2015 from http://www.clotcare.com/faq_inrreliability.aspx.
  3. Roche CoaguChek® XS Meter Package Insert. Retrieved March 9, 2015 from web site: http://www.apsfa.org/docs/XS%20Strip%20Package%20Insert.pdf
  4. Hoel, Robert, et al. Correlation of Point-of-Care International Normalized Ratio to Laboratory International Normalized Ratio in Hemodialysis Patients Taking Warfarin. Clin J Am Soc Nephrol. 2009 Jan; 4(1): 99–104 Retrieved March 25 from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2615705/