1. A.J. Bakker, D. Jager, G. Dijkstra
Evaluation of a semiquantitative dipstick for the determination of microalbuminuria
A.J. Bakker, D. Jager, G. Dijkstra
Stichting Klinisch
Chemisch Laboratorium
Postbus 850
NL 8901 BR Leeuwarden
Klinische Nucleaire Klinische
Chemie Geneeskunde Fysica
Introduction:
Microalbuminuria is an important risk indicator for the development of diabetic nephropathy and cardiovascular diseases. Reliable semi-quantitative methods (applicable for primary healthcare) allow easy and much earlier detection. Here, we report an evaluation of the semi-quantitative Immunodip dipstick test supplied by DCL.
Patients:
205 patients (n=205) who subsequently supplied urine samples for determination of microalbuminuria were enrolled in this study. Analysis took place on the day the urine was delivered to the laboratory.
Methods of analysis:
The DCL Immunodip method (Menarini; prod.no.: ) for determination of microalbuminuria was performed according to manufacturers’ instructions. Results were divided in 5 classes: <12 mg/l (negative); mg/l (threshold); 20 mg/l, 40 mg/l and 80 mg/l (positive).
Stability of the colour after reading was checked after 1, 3, 7 and 30 days.
Quality control was performed with a negative urine and a low (± 18 mg/l) and a high (± 80 mg/l) control based on a saline diluted standardserum (DAKO X0908).
Analysis of microalbumin and creatinine was performed using a Modular anlyzer (Roche):
Microalbuminuria was determined using a home-made procedure in which urine was mixed with phosphate buffered PEG-6000 buffer (10 mmol/l phosphate, pH=7.4, 4.5% PEG-6000). After 5 min a 10-fold diluted DAKO anti-human-albumin antiserum (Q328) in phosphate buffered saline started the reaction (volume sample/buffer/antiserum: 10µl/216µl/36µl; ref. value 16 mg/l).
Creatinine: the Jaffé method (rate-blanked and compensated) was used according to the Roche instructions (Roche, prod.no.: ).
Albumine-creatinine ratio was calculated from corresponding results (ref.value for men 1.8 g/mol and for women 2.5 g/mol).
Patient comparison (n=188):
Sensitivity: 98.0%; Specificity: 89.1%
Likelihood ratio: LR+: 8.9; LR–: 44.5
Sensitivity: 90.4%; Specificity: 86.7%
Likelihood ratio: LR+: 6.8; LR– : 9.0
Colourstability Immunodip:
The colour of the DCL Immunodip teststrips remains stable at room temperature. The interpretation of the majority of the samples did not change after 1, 3, 7 and 30 days for 96.1%, 95.6%, 95.6% and 77.9% of the strips. The colour changes resulted in a higher outcome except for 5 (2.4%) samples which had a borderline result on the first day and a negative result after day 1-30 (graph shown below).
Stability:
Within-run reproducibility of the DCL Immunodip teststrips was tested with a control (diluted serum) at an albumin concentration of 18 mg/L. Between-run reproducibility was tested using control samples every day when analysis were performed (results shown by graphical representation). 80
12-18
neg
within / between day 5
136 1 14 8 2 17 9 40 20
Conclusion
The Immunodip dipstick for microalbumin reliably detects albumin concentration (relation with albumin-creatinine ratio as expected is less good). This Immunodip dipstick is suitable for reliable exclusion of microalbuminuria (Sacks et al. Clin Chem 2002;48: ), but positive results should be confirmed by a quantitative procedure. The colour of the Immunodip dipstick remains stable for at least a week.