Using urine nitrite sticks to test for urinary tract infection in children aged < 2 years: a meta-analysis

Abstract

Background This study aimed to determine whether nitrite sticks are as sensitive at detecting urinary tract infection (UTI) in children <2 years as they are in older children. Methods I reanalysed data on using nitrite sticks to detect UTIs for children aged either < 2 or 2–18 years. For sensitivity, evidence of a UTI was defined as level 1 when a single uropathogen grew ≥ 10 5 colony forming units/ml (cfu/ml) in two urine samples, level 2 when just one sample was cultured or a threshold of < 10 5 cfu/ml was used, and level 3 if mixed growths or Staphylococcus albus was considered to be positive. For specificity, children were defined as uninfected if they had 1 sterile urine culture. I also reanalysed our previously published data by age. Results The sensitivity was lower for children aged < 2 years (11 studies, 1321 subjects) than for older children (9 studies, 295 subjects), whether the level-1 values or all the studies were analysed (Fisher’s exact test, p < 0.0001 for both). The level-1 sensitivities were 0.23 in the infants and 0.81 among older children (odds ratio = 0.07, 95% confidence interval 0.03–0.18). The specificity was very high in infants (10 studies, 1783 cases) and older children (7 studies, 5952 cases), at 0.990 and 0.996. Conclusions Nitrite sticks only have a 23% sensitivity in children aged < 2 years, so cannot reliably rule out UTIs. A positive nitrite stick test is about 99% likely to indicate a UTI in children of any age.

On the Binormal Predictive Receiver Operating Characteristic Curve for the Joint Assessment of Positive and Negative Predictive Values

“…Let us compare Figure 4 with the corresponding leaf plot [ 7 , 8 ]. To do so, we require values of TPP and TNP for the test characterized by the risk score threshold value of s opt = 3.23 on the PROC curve for Example 5 ( Table 2 ).…”

“…At least in part, this is likely because PPV and NPV vary with prevalence. The effect of prevalence on predictive values was illustrated diagrammatically by Sackett et al, see Figures 4−9 and 4−10 of [ 4 ], and more recently by Coulthard [ 7 ] and by Coulthard and Coulthard [ 8 ] as the leaf plot. This diagram shows how the posterior probabilities PPV and 1−NPV vary with prevalence, given the TPP and TNP values of the test in question.…”

“…The approach taken is to place the PROC curve in the context of some other methods for the statistical evaluation of probabilistic disease forecasts. In particular, we discuss the receiver operating characteristic (ROC) curve [ 4 , 5 ], the index of separation PSEP [ 6 ], and the leaf plot [ 7 , 8 ], in terms of their relationship to the PROC curve. The article is set out as follows.…”

Defining urinary tract infection by bacterial colony counts: a case for 100,000 colonies/ml as the best threshold

“…The possible urine tests for UTIs can be divided into those that detect the presence of bacterial themselves and those which detect associated changes, such as increased white blood cell (WBC) numbers or nitrite concentrations. Unfortunately it has always been known that urinary WBC numbers have low diagnostic power [7]; they are neither sufficiently sensitive (they may disappear rapidly [8]) nor specific (they are often present in many children with fever from other causes [9]), and recently it has been shown that urine nitrite sticks miss 77% of UTIs in infants [10]. We are therefore left dependent upon identifying bacteria in urine to make a reliable laboratory diagnosis of UTI in children.…”

“…Incorporating point-of-care screening Unfortunately, nitrite sticks, which are the most convenient point-of-care urine test to detect UTI in older children, miss three-quarters of cases in children aged < 2 years, so they cannot be used to exclude the diagnosis in the most vulnerable children [10]. Figure 4 shows leaf plots for both age groups.…”