Interpretation of the nitroblue-tetrazolium test in regularly dialysed patients

Impaired polymorphonuclear leukocyte function in chronically hemodialyzed patients with iron overload

Polymorphonuclear (PMN) leukoyte function tests and clinical data analyses were performed in 28 chronic renal failure (CRF) patients receiving regular hemodialysis. We divided them into two groups; 12 patients with normal serum ferritin were classified as group 1 and 16 patients with high serum ferritin as group 2. There was no difference in age, BUN, serum creatinine, complement (C3, C4), peripheral white blood cell count and the duration of dialysis between the two groups, but the serum iron level was higher in group 2 (129.1 ± 46.58 μg/dl) than in group 1 (74.3 ± 20.9 μg/dl) (p<0.001). The total iron binding capacity was lower in group 2 (p<0.05) and the number of transfusions was higher in group 2 (25 ± 16.1) than in group 1 (12 ± 8.7) (p<0.05). The nitroblue-tetrazolium (NBT) test showed no difference among groups 1, 2 and the healthy control group. In chemotaxis to fMLP (N-formylmethionylleucylphenylalanine), the mean number of migrated neutrophils to fMLP (10⁻⁶ M/L) per high power field was significantly decreased in group 2 (99.5 ± 37.6) compared with the healthy control group (140.1 ± 13.4) (p<0.005), but not in group 1 (155.8 ± 79.4). In the phagocytosis test using Staphylococcus aureus, the phagocytic index ratio compared to the healthy control group was significantly decreased in group 2 (0.59 ± 0.14), but not in group 1 (0.97 ± 0.18). These results suggest that iron overload due to multiple transfusions in patients receiving regular long term hemodialysis may play a part in causing susceptibility to infection by impairing PMN leukocyte functions, especially chemotaxis and phagocytosis.

[Capacity of nitroblue tetrazolium-reduction of neutrophilic granulocytes (author's transl)]

A modification of the NBT-reaction is described which allows a differentiation of the NBT uptake and NBT-reduction. By means of this method it has been shown that the capacity of NBT-reduction of neutrophil granulocytes taken from hematologically healthy persons is independent of the probands' age and, moreover, of the presence of acute infections and their etiology. It has been shown, that the increase in the NBT-reduction of neutrophilic granulocytes of newborns and persons with acute bacterial infections results from an increased NBT-ingestion. To grive an example of a strongly reduced capacity of NBT-reduction of the neutrophilic granulocytes 2 patients suffering from fatal granulomatous disease in childhood have been examined.

The nitroblue tetrazolium (NBT) test in renal transplantation

The nitroblue tetrazolium (NBT) test has been evaluated as a means of differentiating episodes of infection and rejection in 10 cadaver kidney transplant recipients. Normal NBT values were observed during all 11 episodes of acute rejection. A significant elevation of the NBT score was encountered in six of eight episodes of infection after transplantation. A positive NBT result is useful additional evidence in favour of infection in patients in whom the differentiation of infection and rejection is proving difficult.

A further application of the nitroblue tetrazolium test

The nitroblue tetrazolium (N.B.T.) test was performed on patients in whom a differential diagnosis of pulmonary thromboembolism or lobar pneumonia existed. The mean N.B.T. score in healthy subjects was 6.4% (range 1%-15%). Patients with uncomplicated pulmonary thromboembolism showed a mean N.B.T. value of 7.5% (range 3%-12%). In patients with lobar pneumonia the mean N.B.T. score was 42.4% (range 21%-85%). These results suggest that the N.B.T. test is of value in the differential diagnosis of pulmonary thromboembolism and lobar pneumonia.

Human leucocytes and infection

When infection has occurred almost every type of leucocyte has a function which can contribute to the patient's recovery. Cooperation between different leucocytes takes place, and these cellular activities persist until all microorganisms have been controlled. A deficiency of one particular leucocyte function can often be compensated for by extra activity of another.

In the presence of severe infection many leucocyte functions in vitro, have been shown to be altered, often in a direction which might indicate immunodeficiency. These findings are probably secondary phenomena caused by a relative excess of antigen or of particulate debris. Various drugs can also reduce leucocyte function. All these points need consideration during the investigation of children or adults who have chronic refractory infections.