Bacteria that cause a urinary tract infection (UTI) produce an enzyme that converts urinary nitrates to nitrites. The presence of nitrites in urine indicates a UTI.-
TIME TO STOP DIPPING YOUR URINE AND DO A LAB ,UA , CULTURE AND SENSITIVITY -- this will nail down if it is just faulty sticks or what you have- UTIs in pregnancy silent or not can have some serious consiquences.
here is some specific info about what makes a positive or negative on the dip--
Many gram-negative and some gram positive bacteria are capable of producing this reaction, and a positive test suggests their presence in significant numbers (i.e. more than 10,000 per ml). A negative result does not rule out a urinary tract infection.1,28
Thereagentt is highly sensitive to air exposure, which may cause a false positive response.29
False negative results may be seen where bladder incubation time is shortened (less than 4 hours)9, in the absence of dietary nitrate9, in the presence of nitrate-reductase negative organisms (e.g. some Mycobateria strains30), when urine specific gravity is elevated1, where pH is less than 6.01, and in the presence of urobilinogen9 and urinary vitamin C31.
Here is a quote from a 2000 study--
" Nitrates were found to have a very high specificity (92.4%) for detecting UTI, which is similar to previously reported studies....If all the indices (blood, protein, leucocyte esterase, and nitrates) were combined, and the urine sent for culture if any of these were positive, the sensitivity increased to 97.7% and the chance of missing a UTI was very small."