H and H: H and H, sometimes written as "H&H", is a popular shorthand for hemoglobin and hematocrit, two very common and important blood tests.

Hemoglobin is the oxygen-carrying protein pigment in the blood, specifically in the red blood cells. In the test for hemoglobin (Hb), it is usually measured as total hemoglobin expressed as the amount of hemoglobin in grams (gm) per deciliter (dl) of whole blood, a deciliter being 100 milliliters.

The normal ranges for hemoglobin depend on the age and, beginning in adolescence, the sex of the person. The normal ranges are:

• Newborns: 17-22 gm/dl
• One (1) week of age: 15-20 gm/dl
• One (1) month of age: 11-15gm/dl
• Children: 11-13 gm/dl
• Adult males: 14-18 gm/dl
• Adult women: 12-16 gm/dl
• Men after middle age: 12.4-14.9 gm/dl
• Women after middle age: 11.7-13.8 gm/dl

All of these values may vary slightly between laboratories. Some laboratories do not differentiate between adult and "after middle age" hemoglobin values.

The hematocrit is the proportion, by volume, of the blood that consists of red blood cells. The hematocrit (hct) is expressed as a percentage. For example, an hematocrit of 25% means that there are 25 milliliters of red blood cells in 100 milliliters of blood: a quarter of the blood consists of red cells.

The normal ranges for hematocrit are dependant on age and, after adolescence, sex. The normal ranges are:

• Newborns: 55-68%
• One (1) week of age: 47-65%
• One (1) month of age: 37-49%
• Three (3) months of age: 30-36%
• One (1) year of age: 29-41%
• Ten (10) years of age: 36-40%
• Adult males: 42-54%
• Adult women: 38-46%

These values may vary slightly between laboratories.