Biochemical Interfering Factors and Blood Cells Indices

A complete blood count measures several components and features of blood cells and gives important information about them. In most clinical laboratories, there are three types of automated machines used for blood counts including electrical impedance counter, optical method counters, and flowcytometry (1, 2). These automated instruments can estimate the different red blood cells (RBC) indices, platelets (Plt), and white blood cells (WBC) counts (3). Impedance offers a simple method for counting blood cells (4). Due to the principle used in this method, different factors in analytical and preanalytical stages can affect the results of test. The presence of interfering substances is the most common preanalytic factor that can affect the precision and accuracy of the results produced by impedance cell counter. These substances are classified as endogenous and exogenous interferences (5, 6).

Endogenous interferences consist of some important factors such as hemolysis, bilirubinemia, lipemia, hyperglycemia, and paraproteinemia. Exogenous interferences include drugs and chemical additives that are used in some devices (3, 5, 6). Hyperlipidemia as an endogenous interference manifests as abnormally increased lipids or lipoproteins in the blood. It is classified in two types: primary and secondary (7). Hyperlipidemia causes increase in hemoglobin and MCHC especially in cases with higher serum turbidity. Hyperlipidemia can also increase the WBC count (3, 8, 9). Alteration of plasma lipids leads to an enhanced RBC aggregation (10).

Hyperglycemia (high blood sugar) occurs when an excessive glucose circulate in plasma (11). In automated cell counters, severe hyperglycemia results in falsely high mean corpuscular volume (MCV). This effect seems to be secondary to the osmotic imbalance between RBCs and the diluents used in cell counters. The diversity of cell sizes depend on the temperature, glucose concentration, and the type of cell counter (3, 12, 13). Uremia affects RBCs mechanical properties such as deformability and fragility that results in morphologically deformed erythroid cells (echinocytes) (14). The frequency of clinical laboratory interferences are difficult to determine; hence, they are largely underestimated (6, 15).

This study evaluates the effects of biochemical Interfering factors include hyperglycemia, hyperlipemia, and uremia on blood cells indices like the different RBC indices, Plt, and WBC count.

In the case group of uremia, there were 198 (54%) men and 168 (45%) women; in hyperglycemia group there were 192 (52%) men and 174 (48%) women; there were 178 (49%) men and 188 (51%) women in hyperlipidemia group. The average age of participants was 49.48 ± 3.2, 43.67 ± 2.8, and 45.89 ± 1.9 respectively. The mean age of control group was 46.32 ± 2.7 and this group consisted of 58 48% men and 62 52% women. In addition, the average level of urea, glucose, triglyceride, and cholesterol in patients’ plasma were 92 ± 2.1, 217 ± 1.9, 346 ± 2.1, and 241 ± 2.5, respectively. The levels of these parameters in control group were 25, 81, 105, and 165, respectively. Statistical analysis of these biochemical parameters and their comparison with the control group were shown in separate tables. In case of uremia, there was a statistically significant different between case and control groups with regard to Hb, RBC count, and Hct (P < 0.05) (Table 1).

With regard to hyperlipidemia, comparison between patient and control groups revealed a significant difference between patient and control groups in the levels of Hb, Hct, and MCV (P < 0.05).

Statistical analysis of patients with hyperglycemia revealed that MCV and Hct have significant different (P < 0.05) in these two groups; however, there was no significant different in the levels of RDW, MCH, and MCHC (P > 0.05).

Different factors in preanalytical and analytical stages have influences on tests results produced by impedance cell counter. Some of these factors cause rejection of the samples and some of them interfere with the results of the tests (5, 6). In order to minimize these effects, the sample must be rejected if some problems were observed in it. These problems include improper collection, inadequately labeled sample, improper collection containers, and inappropriate storage temperature (5).

Hyperlipidemia is usually associated with increase of hemoglobin concentration, MCHC, and WBC count (3, 8, 9). In our study, hyperlipidemia with increased level of both triglyceride and cholesterol caused a significant increase in most blood cell count indices include Hb, Hct, MCV, MCH, and Plt count (P < 0.05); on the other hand, MCHC and RDW indices remained unchanged. Sadeghian et al. showed hypertriglyceridemia can falsely increase MCHC but cannot alter MCV or MCH and hypercholesterolemia does not alter the red cell indices (9). Sandberg et al. reported increased in hemoglobin concentration with elevated amounts of lipid in the samples in some cell counters (16).

Uremia is a condition resulting from the accumulation of organic waste products and causes true thrombocytopenia and spurious leukopenia. Although renal transplantation and dialysis are the treatment of uremia, because of short supply of kidney donors, the most effective treatment is dialysis (14). The result of our study showed that uremia caused an increased in the MCV and RDW (P < 0.05) and a decrease in RBC count, Hb, Hct, and MCHC (P < 0.05); on the other hand, it had no effect on platelet count and MCH (P > 0.05).

Hyperglycemia is a condition with high amount of glucose in blood stream and results in falsely high mean corpuscular volume (MCV) due to the osmotic imbalance between red blood cells and the diluents (3, 12, 13). Strauchen et al. added glucose to normal blood at the concentrations of 1000 and 2000 mg/dL that resulted in consistent elevation of the MCV and hematocrit and depression of the MCHC in contrast to control samples without such a hyperglycemic environment (13). Planas et al. showed that the spurious macrocytosis in electronic cell counters was due to hyperglycemia (12).

According to the results of this study and other similar works, we recommend that the effect of interferences such as hyperlipidemia, hyperglycemia, and uremia on impedance cell counter test results must be considered in clinical laboratories and appropriate measures must be evaluated to correct these errors.