Dangerously low hemoglobin levels
There is much debate regarding which hemoglobin level that should be considered dangerously low among doctors and there is no clear cutoff point. The common definition is that it is the level at which a doctor will transfuse red blood cells to avoid complications and it is placed between 7 grams per deciliter in a previously healthy adult with no heart problems to 8.8 grams in a critically ill patient with a previous heart condition especially heart attacks.
At such low levels of hemoglobin, symptoms tend to be severe including severe fatigue and weakness, awareness of a racing heartbeat, fainting and severe dizziness. At such levels, the body can’t get enough oxygen and tries to compensate by increasing the heart rate to better deliver oxygen to tissues which causes the patient to feel that their heart is racing. This can be enough until a certain level when the heart contracts so quickly that it barely relaxes to fill with blood -heart filling occurs during the relaxation phase-. This will eventually cause heart failure which is the cause of death in anemia. Other symptoms can also include chest pain similar to that seen in heart attacks because there is a mismatch between the work the heart does and the oxygen delivered to its muscle. This pain is commonly felt like a tightening sensation underneath the breastbone which is exacerbated by work and exercise and relieved partially or totally at rest.