Immunohematology and diabetes testing

Immunohematology

Formerly called the blood bank, the immunohematology department of the laboratory is responsible for blood typing and cross-matching blood units for transfusion. The major reason for performing immunohematology tests is to prevent problems caused by incompatible blood types during blood transfusions. Compatibility testing (also called cross-matching) is performed to prevent transfusion reactions in patients receiving blood from a donor. Identifying potential Rh incompatibility problems in expectant mothers is another procedure done in immunohematology. Rh incompatibility between an expectant mother and the unborn child may result in hemolytic disease of the newborn (HDN), also known as erythroblastosis fetalis.

Blood typing

There are many blood antigen blood types. The two major blood antigen systems are the ABO system and the Rh system. The ABO system has four major blood groups: A, B, O, and AB. Patients with type AB blood are considered universal recipients. Patients with type O blood are considered universal donors. Another major blood group is the Rh group. A person is either Rh positive (Rh+) or Rh negative (Rh−). Determinations of ABO and Rh blood groups are simple tests that can be performed easily. But because the consequences of performing the test incorrectly can be life threatening, blood typing is not a CLIA-waived test.

Blood type populations

This table gives you an idea of the blood type frequency in a few different populations in the United States.

Type	Caucasian	African-American	Asian	Latino-American
O+	37%	47%	39%	53%
O−	8%	4%	1%	4%
A+	33%	24%	27%	29%
A−	7%	2%	0.5%	2%
B+	9%	18%	25%	9%
B−	2%	1%	0.4%	1%
AB+	3%	4%	7%	2%
AB−	1%	0.3%	0.1%	0.2%

Other blood types

In addition to the A and B antigens that characterize the ABO blood grouping, more than 600 antigens and more than 20 other blood antigen systems are known. Many are named after the person or family in which the blood antigen system was discovered. A medical assistant should be aware that other blood antigens exist. They may cause incompatibility issues in rare cases.

Blood compatibility

RBC Antigen	Plasma Antibodies	Compatible With Donor Type
Type O (no antigens)	Anti-A and Anti-B	O
Type A (A antigen)	Anti-B	O and A
Type B (B antigen)	Anti-A	O and B
Type AB (AB antigen)	None	O, A, B, and AB

Legal and ethical issues related to blood transfusion

The Blood Safety Act was passed in 1991 to ensure that all donor blood is tested for human immunodeficiency virus (HIV) and other blood-borne pathogens. The impact of this law can be seen in the ambulatory care environment. The law requires providers to explain to each elective surgery patient the chances that they may need a blood transfusion. The discussion must include positive and negative aspects of autologous transfusion (i.e., transfusion with a person’s own blood). The pros and cons of transfusions from family, friends, or other donors should also be discussed. The conversation must be documented in the patient’s health record. Before the surgery, the patient must sign a form giving consent to any needed blood transfusions. The medical assistant should be aware that certain populations (e.g., Jehovah’s Witnesses) do not believe in blood transfusions.

If the patient decides to use autologous transfusions, this may require the patient to donate blood several weeks before the procedure. Usually, autologous transfusions are performed for stable patients undergoing major orthopedic, vascular, cardiac, or thoracic surgery. The medical assistant might need to help make arrangements for the blood donation. Another type of autologous transfusion can occur if the surgeon inserts an autologous drain in the surgical wound. The drain collects the blood from the surgical wound to prevent postoperative hematomas. The collected blood is then washed and re infused into the patient.

Blood chemistry in the physician office laboratory

CLIA-waived chemistry tests using whole blood from capillary punctures have become popular in ambulatory practices. With the increase in diabetes and cardiovascular disease in the United States, patients with either (or both) of these metabolic diseases benefit from early diagnosis. Treatment is based on continued monitoring of glucose and hemoglobin A1c for diabetes and of cholesterol, lipid panels, and liver enzymes for cardiovascular diseases related to fatty deposits in the arteries.

Blood glucose testing

Glucose is used as a fuel by all body cells. Under normal circumstances, it is the only substance used to nourish brain cells. Maintenance of blood glucose levels within a normal range is vital to homeostasis of the human body. Understanding the importance of glucose can help the medical assistant understand why glucose is the most frequently tested chemical analyte in the blood.

Elevated blood glucose levels are most often associated with diabetes mellitus. They also may indicate pancreatitis, endocrine disorders, or chronic renal failure. Diabetes mellitus is a disorder of carbohydrate metabolism that results in elevated blood and urine glucose levels. In diabetes mellitus, either the pancreas is unable to produce sufficient insulin to meet the body’s needs, or insulin resistance develops at the cellular level.

For the initial screening of a patient for diabetes type 2, a fasting blood sample is usually taken in the morning, after a fast of 10 to 12 hours. The patient’s fasting blood glucose (FBG) level should be less than 100 mg/dL. If it is higher than 105 mg/dL, the provider may request a blood glucose tolerance test (GTT). For this test, the fasting patient receives a sugary liquid to drink that contains 100 g of glucose. (The amount may be adjusted according to the patient’s weight.) A blood glucose level of less than 140 mg/dL after 2 hours is normal. A reading of more than 200 mg/dL after 2 hours may indicate diabetes. A reading between 140 and 199 mg/dL indicates impaired glucose tolerance, or prediabetes.

Home glucose monitoring

Many CLIA-waived glucometers are available for professional and at-home use. The process the medical assistant uses in the ambulatory care facility for testing blood glucose is very similar to what the patient does at home.

Home glucose monitoring is part of the treatment plan for diabetes mellitus (DM) management. Patients with type 1 DM or type 2 DM may need to test their blood glucose several times a day. Glucose levels may also be monitored by women with gestational diabetes, a condition seen during pregnancy in which the effect of insulin is partially blocked by hormones produced by the placenta.

The medical assistant may need to coach patients on how to test their blood glucose. If the patient’s glucose monitor is available, it is helpful to demonstrate the procedure using the monitor the patient will use. The patient should also do a return demonstration so the medical assistant can ensure that the patient is performing the procedure accurately.

When coaching a patient on using the glucose monitor, the medical assistant should discuss the following topics:

• Equipment and supplies required, and how to dispose of sharps

• How to calibrate the monitor when using new container of test strips

  How to perform a capillary puncture, which includes finding and cleaning the site, lancets to use, disposal of lancets, and how to apply the blood to the test strip

• How to run the test, read the result, and how to document the results (if needed by the provider). Some monitors allow patients to upload their test results using the patient portal; thus the provider can see the results between visits.

Hemoglobin A1c testing

Several methods can be used to measure the hemoglobin A1c level, including CLIA-waived handheld devices. Hemoglobin A1c is also described as glycosylated hemoglobin (sugar-coated hemoglobin). Glycosylated hemoglobin is the result of glucose irreversibly binding to the hemoglobin molecules in the RBCs. It is also referred to as the A1c.

RBCs have a life span of approximately 120 days. Measuring the amount of glucose that has been irreversibly bound to hemoglobin provides an assessment of the average blood glucose during the 60 to 90 days before the test. The A1c test is performed every 3 months in patients with diabetes to monitor the person’s average blood glucose level during those months. An A1c value higher than normal indicates that the average blood glucose has been elevated during the past 2 to 3 months. A normal A1c level for a person without diabetes ranges from 4% to 5.6%. For patients with diabetes, the goal is to maintain the glycosylated hemoglobin level below 7%. With higher levels, the risk of developing complications from diabetes increases.

Home A1c monitoring

Home A1c monitoring does not replace home blood glucose monitoring. Home A1c monitoring is another tool for the management of DM. Patients can perform A1c testing at home using instruments approved by the US Food and Drug Administration (FDA), such as the A1CNow SelfCheck (Bayer) and the in2it (II) Self-Test A1c System (Bio-Rad). The medical assistant may need to coach the patient on home A1c monitoring. The same topics addressed in the Home Glucose Monitoring section would apply to home A1c monitoring.