What parameters on a complete blood count (CBC) indicate anemia and its specific type in a patient with chronic kidney disease (CKD) stage 2 or 3a?

CBC Parameters for Detecting Anemia and Determining Type

Hemoglobin (Hb) is the single most important parameter for detecting anemia, with values <13.0 g/dL in males and <12.0 g/dL in females defining anemia in CKD patients. 1

Primary Parameters for Detecting Anemia

Hemoglobin (Hb) - The Gold Standard

• Hemoglobin should be your primary measure because it is more accurate and stable than hematocrit, with coefficient of variation one-half to one-third that of hematocrit 1
• Hb remains stable at room temperature during storage, while hematocrit falsely elevates by 2-4% with prolonged storage 1
• In hyperglycemia, hematocrit is falsely elevated but hemoglobin remains accurate 1
• Normal values: Adult males/post-menopausal females 15.5 ± 2.0 g/dL; menstruating females 14.0 ± 2.0 g/dL 1

Hematocrit (Hct) - Secondary Measure

• Less reliable than hemoglobin but still useful for trending 1
• Normal values: Adult males/post-menopausal females 47 ± 6%; menstruating females 41 ± 5% 1
• Avoid using as primary measure due to storage instability and analyzer variability 1

Parameters for Determining Anemia Type

Mean Corpuscular Volume (MCV) - Critical for Classification

• Microcytosis (low MCV) indicates iron deficiency, aluminum excess, or hemoglobinopathies 1
• Normocytosis (normal MCV) is typical for CKD-related anemia and represents 80.5% of cases with Hb ≤11 g/dL 1, 2
• Macrocytosis (high MCV) suggests vitamin B12 or folate deficiency, or can occur with iron excess/erythropoietin therapy shifting immature reticulocytes into circulation 1
• In severe anemia (Hb ≤9 g/dL), microcytic anemia represents 24.9% of cases, indicating iron deficiency becomes more prominent with worsening anemia 2

Mean Corpuscular Hemoglobin Concentration (MCHC)

• Normochromic pattern is typical for CKD anemia 1
• Hypochromic pattern suggests iron deficiency 1

White Blood Cell (WBC) Count

• Abnormal WBC count may indicate bone marrow dysfunction from malignancy or vasculitis 1
• Essential for excluding systemic causes beyond simple CKD-related anemia 1

Platelet Count

• Abnormal platelet count suggests generalized bone marrow disturbance rather than isolated erythropoietin deficiency 1
• Helps differentiate CKD anemia from hematologic malignancies 1

Reticulocyte Count - Essential Add-On

• Elevated reticulocyte count (corrected for anemia degree) indicates active hemolysis, such as hemolytic uremic syndrome 1
• Low reticulocyte index despite anemia indicates inappropriate bone marrow response, typical of CKD anemia 3
• This parameter is not standard on basic CBC but should be requested when evaluating anemia etiology 1, 3

Iron Parameters - Mandatory for Complete Evaluation

While not part of the standard CBC, these are essential companion tests:

Transferrin Saturation (TSAT)

• TSAT ≤20% indicates insufficient iron available for hemoglobin synthesis 3, 4, 5
• Reflects iron immediately available for erythropoiesis 1

Serum Ferritin

• Ferritin <100 ng/mL indicates absolute iron deficiency in CKD patients 3, 4
• Iron deficiency is present in 25-37.5% of CKD patients with anemia 1, 4
• Critical finding: 82.7% of patients with microcytic anemia and 58.8% with normocytic anemia (Hb ≤11 g/dL) have low ferritin (<100 μg/mL), meaning iron deficiency commonly coexists with CKD anemia even when MCV is normal 2

Clinical Context for CKD Stage 2-3a

• In CKD stage 2, anemia prevalence is 8.7% in diabetics versus 6.9% in non-diabetics 1
• In CKD stage 3, anemia prevalence is 7.5% in diabetics versus 5.0% in non-diabetics 1
• Anemia develops consistently when GFR falls below 60 mL/min/1.73 m² (stage 3 CKD) 1
• Hemoglobin should be measured at least annually in all CKD patients regardless of stage 1

Common Pitfalls to Avoid

• Do not rely on hematocrit alone - it falsely elevates with storage time and hyperglycemia 1
• Do not assume normocytic anemia excludes iron deficiency - over 60% of normocytic anemia cases in CKD have depleted iron stores 2
• Do not skip iron studies - iron deficiency is present in up to 37.5% of CKD anemia cases and must be corrected before considering erythropoietin therapy 1, 3, 4
• Do not ignore WBC and platelet counts - abnormalities suggest bone marrow pathology beyond CKD 1