Total Hemoglobin (Hb)
Total hemoglobin (Hb) is used to measure the amount of Hb found in a deciliter (dl, or 100 ml) of whole blood. It's usually part of a complete blood count. Hb concentration correlates closely with the red blood cell (RBC) count.
- To measure the severity of anemia or polycythemia and to monitor response to therapy
- To obtain data for calculating mean corpuscular Hb and mean corpuscular Hb concentration
- Explain to the patient that this test is used to detect anemia or polycythemia, or to assess his response to treatment.
- Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
- Reassure him that drawing a blood sample will take less than 3 minutes.
- Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
- If the patient is an infant or child, explain to the parents that a small amount of blood will be taken from the finger or earlobe.
- Inform him that food or fluids need not be restricted before the test.
Procedure and posttest care
- For adults and older children, perform a venipuncture, and collect the sample in a 7-mllavender-top tube.
- For younger children and infants, collect capillary blood in a pipette.
- If a hematoma develops at the venipuncture site, apply warm soaks.
- Completely fill the collection tube and invert it gently several times to thoroughly mix the sample and the anticoagulant.
- Handle the sample gently to prevent hemolysis.
Hb concentration varies, depending on the type of sample drawn (capillary blood samples for infants and venous blood samples for all others), and on the patient's age and sex, as follows:
- neonates ages 0 to 2 weeks: 14.5 to 24.5 g/dl
- infants ages 2 to 8 weeks: 12.5 to 20.5 g/dl
- infants ages 2 to 6 months: 10.7 to 17.3 g/dl
- infants ages 6 months to 1 year: 9.9 to 14.5 g/dl
- children ages 1 to 6: 9.5 to 14.1 g/dl
- adult males: 14 to 17.4 g/dl
- adult females: 12 to 16 g/dl.
Low Hb concentration may indicate anemia, recent hemorrhage, or fluid retention, causing hemodilution.
Elevated Hb suggests hemoconcentration from polycythemia or dehydration.
- Failure to use the proper anticoagulant or to adequately mix the sample and the anticoagulant
- Hemolysis due to rough handling of the sample
- Hemoconcentration due to prolonged tourniquet constriction.
- Abnormal RBC size or drawing blood through a small-gauge needle.
- Very high white blood cell counts, lipemia, or RBCs that are resistant to lysis (false-high)
- Dehydration (possible false-high)
- Hemodilution (possible false-low)